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Computational Study of the Ni-Catalyzed C–H Oxidative Cycloaddition of Aromatic Amides with Alkynes

Humair M. Omer
Humair M. Omer
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
More by Humair M. Omer
Peng Liu*
Peng Liu
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States
Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States
*E-mail: [email protected].
More by Peng Liu
http://orcid.org/0000-0002-8188-632X

Cite this: ACS Omega 2019, 4, 3, 5209-5220

Publication Date (Web):March 13, 2019

https://doi.org/10.1021/acsomega.9b00030

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Abstract

The mechanism of Ni-catalyzed ortho C(sp²)–H oxidative cycloaddition of aromatic amides with internal alkynes containing 2-pyridinylmethylamine directing group was investigated using density functional theory (DFT) calculations. The C–H cleavage step proceeds via σ-complex-assisted metathesis (σ-CAM) with an alkenyl-Ni(II) complex. This is in contrast to the more common carboxylate/carbonate-assisted concerted metalation–deprotonation mechanism in related Ni-catalyzed C–H bond functionalization reactions with N,N-bidentate directing groups. In this reaction, the alkyne not only serves as the coupling partner, but also facilitates the σ-CAM C–H metalation both kinetically and thermodynamically. The subsequent functionalization of the five-membered nickelacycle proceeds via alkyne insertion into the Ni–C bond to form a seven-membered nickelacycle. This process proceeds with high levels of regioselectivity to form a C–C bond with sterically more encumbered alkyne terminus. This unusual regioselectivity is due to steric repulsions with the directing group that is coplanar with the alkyne in the migratory insertion transition state. The C–N bond reductive elimination to form the isoquinolone cycloadduct is promoted by PPh₃ complexation to the Ni center and the use of flexible 2-pyridinylmethylamine directing group. The origin of the cis–trans isomerism of alkene byproduct was also explained by computations.

1. Introduction

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Functionalization of C–H bonds to construct new C–C and C–heteroatom bonds using transition-metal catalysts is a powerful, step- and atom-economical strategy in organic synthesis.(1) First introduced by Daugulis et al.,(2)N,N-bidentate directing groups are now widely used to facilitate site-selective C–H bond functionalizations using a variety of transition metals, including Pd, Ni, Ru, Rh, Co, and Cu, as catalysts (Scheme 1).(3,4) The C–H cleavage step in these reactions is most commonly proposed to proceed via a base-promoted concerted metalation–deprotonation (CMD) mechanism.(5) Although other C–H bond metalation pathways, such as oxidative addition (OA),(6) σ-complex-assisted metathesis (σ-CAM),(7) and ligand-to-ligand hydrogen transfer,(8) are well precedented in the literature, these alternative mechanisms have not been thoroughly investigated in C–H functionalization reactions involving N,N-bidentate directing groups.(9) Because previous computational mechanistic studies of this type of reactions all focused on the CMD mechanism,(10,11) it is not clear what conditions would promote an alternative C–H bond cleavage pathway. In addition, factors that control the reactivity of these alternative C–H cleavage pathways have not been investigated computationally.

In this manuscript, we report a computational study of the Ni-catalyzed oxidative cycloaddition of aromatic amides and alkynes via C(sp²)–H functionalization assisted by a 2-pyridinylmethylamine directing group (Scheme 2a).(12,13) In contrast to the C–H functionalization of similar aromatic and aliphatic amides with other coupling partners,(14−18) this oxidative cycloaddition is mechanistically distinct in several aspects. First, unlike the majority of Ni-catalyzed C–H functionalization reactions, which often employs a Ni(II) precatalyst and under conditions with bases (e.g., acetates, carbonates, etc.), this reaction involves a Ni(0) catalyst in the absence of a base. Chatani et al. proposed a unique C–H metalation mechanism via an alkenyl-Ni(II) complex formed from insertion of an alkyne to a nickel(II)-hydride.(12,19) It is surmised that the electron-deficient Ni(II) center would coordinate to the ortho C–H bond to form a σ-complex, which then undergoes σ-complex-assisted metathesis (σ-CAM) of the ortho C–H bond with the Ni–alkenyl bond via a four-membered cyclic transition state (path b, Scheme 1). Second, this oxidative cycloaddition forms the isoquinolone cycloadduct, while reactions of similar substrates with alkynes under different reaction conditions (e.g., in the presence of a base or with O₂ as oxidant) lead to acyclic alkenylation or alkynation products (Scheme 2b,c).(20) These reactions are expected to involve similar Ni(II) metalacycle intermediates regardless of the C–H metalation mechanism (Scheme 1). Factors that determine the chemoselectivity of cyclic versus acyclic products are still not clear. Finally, this oxidative cycloaddition uses alkyne as a mild oxidant,(9,21) which is unusual in oxidative C–H functionalization reactions. In most of the oxidative C–H functionalization reactions,(22−25) the oxidant is not directly involved in the C–H metalation step. In contrast, it has been proposed that the alkyne promotes the reactivity of the C–H metalation step of this reaction.(12) Therefore, the role of the alkyne oxidant warrants an in-depth investigation.

To address these mechanistic ambiguities, we performed density functional theory calculations to investigate the reaction mechanisms of the Ni-catalyzed ortho C(sp²)–H oxidative cycloaddition reaction with alkynes. We provide a detailed analysis of the mechanisms of the C–H metalation step and the role of alkyne in facilitating the C–H metalation. The effects of phosphine additives and 2-pyridinylmethylamine directing group on reactivity and chemoselectivity for the isoquinolone cycloaddition products are carefully analyzed. In addition, the origins of the experimentally observed regioselectivity with unsymmetrically internal aryl alkynes and the formation of trans-alkene byproducts are also rationalized.

2. Results and Discussion

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2.1. Proposed Reaction Mechanisms

The proposed mechanisms of the Ni-catalyzed ortho C(sp²)–H oxidative cycloaddition of aromatic amide 1 with model substrate 2-butyne 2 to afford the isoquinolone cycloaddition product 3 are provided in Scheme 3. With the low-valence Ni(0) precatalyst, coordination of the N,N-bidentate directing group most likely occurs via an oxidative addition of the amide N–H bond to form a Ni(II)-hydride (10) rather than through a base-promoted N–H deprotonation.(26,27) The ortho C–H bond in 10 is expected to yield an agostic interaction with the Ni due to its proximity to the electron-deficient metal center. From 10, two different C–H metalation pathways are possible. The σ-complex-assisted metathesis (σ-CAM) of the ortho C–H bond with the Ni–H bond in 10 will afford the H₂-bound nickelacycle 11.(28) Alternatively, alkyne insertion into the Ni–H bond in 10 will form an alkenyl-Ni(II) complex 8,(29) which then undergoes a σ-CAM with the Ni–alkenyl bond to give the alkene-bound nickelacycle 9. Ligand exchange of the H₂ or alkene in intermediate 11 or 9 with an alkyne yields complex 13. Subsequent alkyne migratory insertion into the Ni–C(sp²) bond in 13 forms a seven-membered nickelacycle, which upon C–N bond reductive elimination gives the isoquinolone product 3 and regenerates the Ni(0) catalyst. As discussed in Introduction, because such σ-CAM pathways have not been investigated computationally, a few important mechanistic questions still remain. These include: (a) the preference of the two competing σ-CAM pathways from either the nickel hydride 10 or the alkenyl nickel complex 8; (b) factors that promote the C–N bond reductive elimination to form the cycloaddition product; (c) factors that promote alkyne insertion into the nickelacycle 13 over the direct alkene migratory insertion from 9; (d) origins of regioselectivity with unsymmetrical internal alkynes; and (e) the mechanism to form the trans-alkene byproduct. These questions are discussed in detail in the following sections.

2.2. Mechanisms of the Ortho C(sp²)–H Metalation Step and the Role of Alkyne as a Hydrogen Acceptor

The computed reaction energy profiles for steps leading to the C–H metalated nickelacycle 9 are shown in Figure 1a. Optimized geometries of select transition states and intermediates are shown in Figure 1b. The catalytic cycle begins with ligand exchange to replace the cod ligands in the Ni(cod)₂ precatalyst with PPh₃ and amide 1 to form complex 4. Under the experimental conditions of 10 mol % Ni(cod)₂, 40 mol % PPh₃ ligand, and three or more equivalents of internal alkyne, cod, PPh₃, or the internal alkyne can potentially bind to the Ni center prior to the amide N–H oxidative addition.(30) The N–H oxidative addition pathways involving these ancillary ligands were considered computationally (see the Supporting Information for details). Our calculations indicate that the most favorable amide N–H oxidative addition pathway involves binding of two PPh₃ ligands (TS1). Facilitated by the strong donor ligands (PPh₃ and pyridine), this N–H oxidative addition process has an activation barrier of 28.0 kcal/mol with respect to 1 and Ni(cod)₂. In the absence of PPh₃, the N–H oxidative addition requires a barrier that is about 5 kcal/mol higher than that of TS1 (see the Supporting Information for details).

From the Ni(II)-hydride intermediate 5, two different σ-CAM pathways are possible. Dissociation of the PPh₃ ligand forms σ-complex 10, which has a strong agostic interaction between the ortho C–H bond and the Ni.(31) This agostic interaction slightly elongates the ortho C–H bond to 1.11 Å compared to 1.09 Å for the same bond in 5. Formation of the σ-complex promotes the σ-bond metathesis of the ortho C–H bond with the Ni–H bond via a four-membered cyclic σ-CAM transition state TS4.(32) The four-membered cycle in TS4 is completely planar, which makes the benzene ring coplanar with the 2-pyridinylmethylamine directing group, resembling the planar geometry of the forming nickelacycle intermediate 11. TS4 is only 9.2 kcal/mol higher in energy than the σ-complex 10. However, because the formation of the Ni(II)-hydride σ-complex 10 is highly endergonic (27.1 kcal/mol with respect to amide 1 and the Ni(cod)₂ catalyst), the overall activation free energy of this σ-CAM pathway is relatively high (ΔG^‡ = 36.3 kcal/mol). An alternative σ-CAM pathway from complex 5 involves a ligand exchange to replace the PPh₃ ligand with an alkyne to form π-alkyne complex 6, which then undergoes facile alkyne migratory insertion (TS2) into the Ni–H bond and forms alkenyl-Ni(II) complex 8.(33) An agostic interaction with the ortho C–H bond was also observed in σ-complex 8, although the distance between the C–H bond and the Ni is slightly longer than that in 10 due to the larger size of the alkenyl group compared to the hydride ligand. From 8, the C–H metalation occurs via σ-CAM transition state TS3, which requires a low activation barrier of 10.8 kcal/mol with respect to 8 to form the alkene-bound five-membered nickelacycle 9.(34) Similar to the planar geometry of TS4, the four-membered cycle in TS3 is also coplanar with the bidentate directing group. The alkenyl group is perpendicular to the plane. Therefore, no significant steric repulsions are observed between the alkenyl group and the directing group in the σ-CAM transition state. Overall, TS3 is much more stable than TS4 because of the greater stability of the alkenyl-Ni(II) complex 8 compared to the Ni(II)-hydride 10. As such, the σ-CAM occurs via the alkenyl-Ni(II) complex 8 rather than from the Ni(II)-hydride 10, consistent with the mechanism proposed by Chatani.(12) Here, the alkyne plays an important role in promoting the C–H metalation via σ-CAM. Although the initial N–H oxidative addition to form the Ni(II)-hydride is kinetically feasible, this process is thermodynamically uphill. In the presence of alkyne, the Ni(II)-hydride intermediate is converted to a thermodynamically more stable alkenyl-Ni(II) complex via alkyne migratory insertion. Due to the thermodynamic stability of the alkenyl-Ni(II) complex, this σ-CAM pathway now requires a much lower overall activation barrier. As the H₂ acceptor, the alkyne also provides thermodynamic driving force for the C–H metalation. While the formation of the cis-2-butene-bound nickelacycle 9 is exergonic, the corresponding C–H metalation process in the absence of alkyne to form the H₂-bound nickelacycle 11 is endergonic by 24.8 kcal/mol with respect to the reactants (1, alkyne, and Ni(cod)₂). Taken together, the alkyne serves multiple roles in promoting the C–H metalation both kinetically and thermodynamically.(35)

2.3. Mechanisms of Ni–C Insertion and C–N Bond Formation Steps and the Effects of Phosphine Additives and the 2-Pyridinylmethylamine Directing Group

We next investigated the mechanisms of the reaction of the nickelacycle intermediate 9 with alkyne to form the experimentally observed isoquinolone product and a few competing pathways to the experimentally unobserved products (Figure 2). From the alkene-bound nickelacycle 9, ligand exchange with another molecule of alkyne forms π-alkyne complex 13, which is 7.8 kcal/mol more stable than 9. The alkyne migratory insertion to the Ni–C bond in 13 forms a seven-membered nickelacycle 14 via transition state TS5. This process is more favorable than the alkene migratory insertion from 9 (via TS8). Here, TS5 is stabilized by the backdonation of the Ni d electrons to the π* of the alkyne, which is not present in TS8.(36) From 14, the C–N bond reductive elimination is promoted by coordination of a PPh₃ ligand to form a four-coordinated Ni(II) complex 15. From 15, the C–N bond reductive elimination (TS6) requires only 13.7 kcal/mol to form the isoquinolone-bound Ni(0) complex 16. On the other hand, reductive elimination from complex 14 without phosphine coordination requires a much higher activation barrier of 24.2 kcal/mol (TS7) with respect to 14.

Experimentally, the Ni-catalyzed ortho C(sp²)–H oxidative cycloaddition reaction is the most effective with 2-pyridinylmethylamine directing group.(12) Although several different N,N-bidentate directing groups, such as 2-pyridinylmethylamine, 8-aminoquinoline, and 2-(pyridin-2-yl)isopropyl amine, have been used experimentally for related transformations, a thorough understanding of potential directing group effects in these reactions is still lacking.(10a,b) We surmised that the flexible directing group in 1 may facilitate the C–N bond reductive elimination to form the cyclic isoquinolone product. We performed calculations with model substrate 19 containing a more rigid 8-aminoquinoline moiety to explore the flexibility effect of the directing group. In reaction with 19, the C–N bond reductive elimination (TS9) requires an activation barrier of 18.9 kcal/mol with respect to the seven-membered nickelacycle 20 (Figure 3), which is more than 6 kcal/mol higher than the corresponding C–N bond reductive elimination using the 2-pyridinylmethylamine directing group (TS6). In TS6, the five-membered N,N-chelate adapts an envelope conformation in which the sp³ carbon (C1) is puckered out of plane. This allows the forming C–N bond to be coplanar with the pyridine N and the PPh₃ ligand such that the Ni(II) center can adopt a less-distorted square planar geometry. On the other hand, the rigid 8-aminoquinoline directing group leads to greater distortion of the fused rings in TS9 that makes the C–N bond reductive elimination less effective.(37)

In summary, the most favorable mechanism in the Ni-catalyzed ortho C(sp²)–H oxidative cycloaddition of aromatic amide 1 and internal alkyne 2 proceeds by oxidative addition into the amide N–H bond to form Ni(II)-hydride 5, followed by alkyne insertion to form an alkenyl-Ni(II) complex 8. The agostic interaction with the ortho C–H bond in the σ-complex 8 promotes C–H metalation via a σ-CAM mechanism to afford alkene-bound five-membered nickelacycle. Insertion of another alkyne molecule and phosphine-promoted C–N reductive elimination afford the isoquinolone product and regenerate the Ni(0) catalyst.

2.4. Origin of Regioselectivity with Unsymmetrical Internal Aryl Alkynes

We next investigated the origin of the high levels of regioselectivity in reactions with unsymmetrical internal alkynes. When phenylalkylacetylenes are used as coupling partners, this oxidative cycloaddition reaction tolerates bulky alkyl substituents, such as tert-butyl, on the alkyne (Scheme 4). Interestingly, the major regioisomeric pathway involves formation of a new C–C bond with the more sterically demanding alkyne terminus. In addition, a greater regioselectivity was observed when the size of the alkyl group increased from methyl to tert-butyl. To investigate the origin of this “counter-steric” regioselectivity, we calculated the regioselectivity-determining alkyne insertion pathways with phenylalkylacetylenes 23 and 24 (Table 1).

Table 1. Regioselectivity in Reactions with Unsymmetrical Alkynesa

^{^a}

Gibbs free energy and enthalpy of activation in the alkyne insertion step. All energies are in kcal/mol with respect to the alkyne-bound nickelacycle C.

In the reaction with 1-phenyl-1-propyne (23, R = Me), the alkyne insertion transition state (TS-10A) leading to the major regioisomer A is preferred by 1.6 kcal/mol, in good agreement with experimental regioselectivity (entry 1). The origin of this preference is attributed to the stabilization of the partial negative charge on the α-carbon of the forming Ni–C bond by the terminal phenyl group in TS-10A.(38) In the reaction with phenyl-t-butylacetylene (24, R = t-Bu), the major regioisomeric transition state TS-11A is stabilized by a similar electronic effect. TS-11A and TS-10A have almost identical activation barriers with respect to the corresponding π-alkyne complexes. Therefore, the reactivity of this migratory insertion is not sensitive to the steric bulk of the terminal alkyne substituent (R) adjacent to the forming C–C bond. The four-membered cyclic alkyne migration transition states TS-11A and TS-10A are not planar; the alkyl group (R) on the alkyne points out of the plane of the nickelacycle (Figure 4). As such, the steric repulsions between R and the nickelacycle in both transition states are diminished. On the other hand, in the minor regioisomeric transition state TS-11B, the bulky tert-Bu substituent is placed coplanar with the nickelacycle to achieve a square planar geometry of Ni(II). As such, substantial steric repulsions between the tert-Bu and the 2-pyridinylmethylamine directing group are observed in TS-11B. This steric effect makes the tert-Bu-substituted TS-11B 1.5 kcal/mol less stable than the Me-substituted TS-10B and thus leads to an increased regioselectivity (ΔΔG^‡ = 3.8 kcal/mol) when phenyl-t-butylacetylene (24) was used as the coupling partner.

2.5. Mechanism of Cis–Trans Isomerization of the Alkene Byproduct

In the Ni-catalyzed C–H bond functionalization of amide 1 with diphenylacetylene, trans-stilbene was produced in 81% yield.(12) The alkyne-promoted σ-CAM process discussed above forms cis-alkenes rather than the trans-isomers. As such, a cis-to-trans alkene isomerization must be operational. Because nickel hydride complexes are known to catalyze alkene isomerization reactions,(27a) we surmised that Ni(II)-hydride intermediate 5 in the main catalytic cycle may serve as a catalyst to promote the cis–trans isomerization. The reaction energy profile of this pathway was calculated (Figure 5).

Ligand exchange of PPh₃ in Ni(II)-hydride 5 with cis-2-butene forms complex 25, which then undergoes alkene migratory insertion to form β-agostic alkyl-Ni(II) complex 27.(39) From 27, β-hydride elimination with a different C–H bond forms the trans-2-butene-bound Ni(II)-hydride 28, which upon ligand exchange with PPh₃ extrudes the trans-2-butene byproduct. The cis–trans isomerization process in this off-cycle pathway is kinetically feasible and thermodynamically exergonic by 0.9 kcal/mol. The presence of PPh₃ ligand does not significantly inhibit the reaction because the ligand exchange of PPh₃ with alkene is only uphill by about 11 kcal/mol. In addition, coordination to a PPh₃ ligand to form 26 does not stabilize the alkyl-Ni(II) intermediate 27. Taken together, the computed reaction energy profile indicates that the Ni(II)-hydride intermediate 5 is a competent catalyst for the isomerization of cis-alkenes to the experimentally observed trans-alkene byproducts. These results further support the formation of Ni(II)-hydride complex in the main catalytic cycle.

3. Conclusions

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The reaction mechanism of Ni-catalyzed ortho C(sp²)–H oxidative cycloaddition of aromatic amides with internal alkynes containing 2-pyridinylmethylamine directing group was investigated using DFT calculations. The catalytic cycle begins by oxidative addition of the amide N–H bond to form a Ni(II)-hydride complex. The subsequent C–H metalation process occurs via a unique σ-complex-assisted metathesis (σ-CAM) mechanism where the internal alkyne acts as a hydrogen acceptor. This contrasts with the CMD mechanism that is usually involved in the Ni-catalyzed C–H metalation in the presence of carboxylate or carbonate bases. The alkyne plays significant roles in promoting the σ-CAM pathway both thermodynamically as a H₂ acceptor and kinetically. Because the Ni(II)-hydride intermediate is thermodynamically unstable, σ-CAM from the Ni(II)-hydride requires a high overall barrier. On the other hand, in the presence of the alkyne, the Ni(II)-hydride is converted to a more stable alkenyl-Ni(II) species, which then undergoes more facile σ-CAM.

The subsequent reaction with the alkene-bound nickelacycle proceeds via an exergonic ligand exchange with another molecule of alkyne, followed by alkyne insertion to form a seven-membered nickelacycle. The insertion of the alkene is less favorable. The alkyne migratory insertion occurs via a nonplanar four-membered cyclic transition state, in which the steric repulsion about the forming C–C bond is diminished. As such, this reaction tolerates alkynes with very bulky terminus and offers high regioselectivity to form the sterically more encumbered C–C bond. The C–N bond reductive elimination of the seven-membered nickelacycle is a key step to form the cyclic isoquinolone products. This C–N bond reductive elimination is promoted by a PPh₃ ligand and the flexible 2-pyridinylmethylamine directing group, which reduces the strain of the fused cyclic system in the reductive elimination transition state. The cis–trans isomerism of the alkene byproduct was also explored computationally. This process is catalyzed by a Ni(II)-hydride intermediate in the main catalytic cycle.

We expect that the mechanistic insights from this study, in particular, the unique roles of alkynes to promote the σ-CAM pathway, will aid in the development of other transition-metal-catalyzed C–H functionalization reactions with alkynes.

4. Computational Methods

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All calculations were performed using Gaussian 09.(40) Images of the 3D structures of molecules were generated using CYLview.(41) Geometry optimizations and vibrational frequency calculations were performed using the B3LYP(42) functional in gas phase with the LANL2DZ effective core potential basis set for nickel and the 6-31G(d) basis set for other atoms. The nature of all stationary points was confirmed by the number of imaginary frequencies. All minima have zero imaginary frequency, and all transition states have only one imaginary frequency. IRC calculations were carried out for alkene and alkyne insertion transition states and for σ-CAM transition states to confirm that the transition state structures connected to the appropriate intermediates. Single-point energy calculations were carried out using the M06(43) functional and the SDD basis set for Ni and 6-311+G(d,p) for other atoms. The SMD(44) solvation model was used in the single-point energy calculations to incorporate solvent effects with toluene as the solvent. Thermal corrections to the Gibbs free energies and enthalpies were calculated using the harmonic oscillator approximation at 298.15 K.

Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.9b00030.

Reaction energy profiles of amide N–H oxidative addition with different ligands (Figure S1), alternative C−H metalation mechanisms with cis-2-butene (Figure S2), via σ-bond metathesis of phosphine-bound Ni(II)-hydride (Figure S3), via oxidative addition to Ni(0) (Figure S4), via deprotonation by the amide N (Figure S5), and C−N reductive elimination with model substrates (Figure S6); Cartesian coordinates of optimized geometries (PDF)

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- ao9b00030_si_001.pdf (999.56 kb)

The authors declare no competing financial interest.

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Acknowledgments

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The authors acknowledge the NSF (CHE-1654122) for funding. Calculations were performed at the Center for Research Computing at the University of Pittsburgh and the Extreme Science and Engineering Discovery Environment (XSEDE) supported by NSF.

References

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Innate and Guided C-H Functionalization Logic
BrUckl, Tobias; Baxter, Ryan D.; Ishihara, Yoshihiro; Baran, Phil S.
Accounts of Chemical Research (2012), 45 (6), 826-839CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
A review. The combustion of org. matter is perhaps the oldest and most common chem. transformation utilized by mankind. The generation of a C-O bond at the expense of a C-H bond during this process may be considered the most basic form of C-H functionalization. This illustrates the extreme generality of the term "C-H functionalization", because it can describe the conversion of literally any C-H bond into a C-X bond (X being anything except H). Therefore, it may be of use to distinguish between what, in our view, are two distinct categories of C-H functionalization logic: "guided" and "innate". Guided C-H functionalizations, as the name implies, are guided by external reagents or directing groups (covalently or fleetingly bound) to install new functional groups at the expense of specifically targeted C-H bonds. Conversely, innate C-H functionalizations may be broadly defined as reactions that exchange C-H bonds for new functional groups based solely on natural reactivity patterns in the absence of other directing forces. Two substrates that illustrate this distinction are dihydrojunenol and isonicotinic acid. The C-H functionalization processes of hydroxylation or arylation, resp., can take place at multiple locations on each mol. Innate functionalizations lead to substitution patterns that are dictated by the inherent bias (steric or electronic) of the substrate undergoing C-H cleavage, whereas guided functionalizations lead to substitution patterns that are controlled by external directing forces such as metal complexation or steric bias of the reagent. Although the distinction between guided and innate C-H functionalizations may not always be clear in cases that do not fit neatly into a single category, it is a useful convention to consider when analyzing reactivity patterns and strategies for synthesis. We must emphasize that although a completely rigorous distinction between guided and innate C-H functionalization may not be practical, we have nonetheless found it to be a useful tool at the planning stage of synthesis. In this Account, we trace our own studies in the area of C-H functionalization in synthesis through the lens of "guided" and "innate" descriptors. We show how harnessing innate reactivity can be beneficial for achieving unique bond constructions between heterocycles and carbonyl compds., enabling rapid and scalable total syntheses. Guided and innate functionalizations were used synergistically to create an entire family of terpenes in a controlled fashion. We continue with a discussion of the synthesis of complex alkaloids with high nitrogen content, which required the invention of a uniquely chemoselective innate C-H functionalization protocol. These findings led us to develop a series of innate C-H functionalization reactions for forging C-C bonds of interest to the largest body of practicing org. chemists: medicinal chemists. Strategic use of C-H functionalization logic can have a dramatically pos. effect on the efficiency of synthesis, whether guided or innate.
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(f) Pototschnig, G.; Maulide, N.; Schnürch, M. Direct Functionalization of C–H Bonds by Iron, Nickel, and Cobalt Catalysis. Chem. Eur. J. 2017, 23, 9206– 9232, DOI: 10.1002/chem.201605657
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1f
Direct Functionalization of C-H Bonds by Iron, Nickel, and Cobalt Catalysis
Pototschnig, Gerit; Maulide, Nuno; Schnuerch, Michael
Chemistry - A European Journal (2017), 23 (39), 9206-9232CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. Non-precious-metal-catalyzed reactions are of increasing importance in chem. due to the outstanding ecol. and economic properties of these metals. In the subfield of metal-catalyzed direct C-H functionalization reactions, recent years showed an increasing no. of publications dedicated to this topic. Nickel, cobalt, and last but not least iron, have started to enter a field which was long dominated by precious metals such as palladium, rhodium, ruthenium, and iridium. The present review article summarizes the development of iron-, nickel-, and cobalt-catalyzed C-H functionalization reactions until the end of 2016, and discusses the scope and limitations of these transformations.
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(g) Chen, Z.; Wang, B.; Zhang, J.; Yu, W.; Liu, Z.; Zhang, Y. Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups. Org. Chem. Front. 2015, 2, 1107– 1295, DOI: 10.1039/C5QO00004A
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1g
Transition metal-catalyzed C-H bond functionalizations by the use of diverse directing groups
Chen, Zhengkai; Wang, Binjie; Zhang, Jitan; Yu, Wenlong; Liu, Zhanxiang; Zhang, Yuhong
Organic Chemistry Frontiers (2015), 2 (9), 1107-1295CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
A review. This review article gives an overview of the development of utilizing the functionalities as directing groups. The discussion is directed toward the use of different functional groups contg. nitrogen, oxygen, sulfur, phosphorus, silicon, π-chelation and bidentate systems as directing groups for construction of carbon-carbon and carbon-heteroatom bonds via C-H activation using various transition metal catalysts. The synthetic applications and mechanistic features of these transformations including arylation, olefination, alkylation, alkynylation, carbonylation, amination, halogenation and so on are discussed. The review is organized on the basis of the type of directing groups and the type of bond being formed or the catalyst.
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(h) Wencel-Delord, J.; Dröge, T.; Liu, F.; Glorius, F. Towards mild metal-catalyzed C–H bond activation. Chem. Soc. Rev. 2011, 40, 4740– 4761, DOI: 10.1039/c1cs15083a
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1h
Towards mild metal-catalyzed C-H bond activation
Wencel-Delord, Joanna; Droege, Thomas; Liu, Fan; Glorius, Frank
Chemical Society Reviews (2011), 40 (9), 4740-4761CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
A review. Functionalization of traditionally inert carbon-hydrogen bonds represents a powerful transformation in org. synthesis, providing new entries to valuable structural motifs and improving the overall synthetic efficiency. C-H bond activation, however, often necessitates harsh reaction conditions that result in functional group incompatibilities and limited substrate scope. An understanding of the reaction mechanism and rational design of exptl. conditions have led to significant improvement in both selectivity and applicability. This crit. review summarized and discussed endeavors towards the development of mild C-H activation methods and wishes to trigger more research towards this goal. In addn., the authors examd. select examples in complex natural product synthesis to demonstrate the synthetic utility of mild C-H functionalization (84 refs.).
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(i) Davies, H. M. L.; Morton, D. Recent Advances in C–H Functionalization. J. Org. Chem. 2016, 81, 343– 350, DOI: 10.1021/acs.joc.5b02818
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1i
Recent Advances in C-H Functionalization
Davies, Huw M. L.; Morton, Daniel
Journal of Organic Chemistry (2016), 81 (2), 343-350CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
A review. This review highlights 24 recent papers and illustrates their significance to the C-H functionalization endeavor. Some of the current trends are covered. E.g., design of new directing groups that are readily removed or converted into useful functionality, broadening the scope from the more traditional functionalization of sp2 C-H bonds to sp3 C-H bonds, application of the methodol. to a broader range of functionality, and modification of the directing influence away from just ortho-functionalization.
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(a) Zaitsev, V. G.; Shabashov, D.; Daugulis, O. Highly Regioselective Arylation of sp3 C–H Bonds Catalyzed by Palladium Acetate. J. Am. Chem. Soc. 2005, 127, 13154– 13155, DOI: 10.1021/ja054549f
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2a
Highly Regioselective Arylation of sp3 C-H Bonds Catalyzed by Palladium Acetate
Zaitsev, Vladimir G.; Shabashov, Dmitry; Daugulis, Olafs
Journal of the American Chemical Society (2005), 127 (38), 13154-13155CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A new palladium-catalyzed arylation process based on C-H activation has been developed. The utilization of pyridine-contg. directing groups allows the β-arylation of carboxylic acid derivs. and γ-arylation of amine derivs. Both primary and secondary sp3 C-H bonds, as well as sp2 C-H bonds, are reactive.
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(b) Nadres, E. T.; Santos, G. I. F.; Shabashov, D.; Daugulis, O. Scope and Limitations of Auxiliary-Assisted, Palladium-Catalyzed Arylation and Alkylation of sp2 and sp3 C–H Bonds. J. Org. Chem. 2013, 78, 9689– 9714, DOI: 10.1021/jo4013628
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2b
Scope and Limitations of Auxiliary-Assisted, Palladium-Catalyzed Arylation and Alkylation of sp2 and sp3 C-H Bonds
Nadres, Enrico T.; Santos, Gerson Ivan Franco; Shabashov, Dmitry; Daugulis, Olafs
Journal of Organic Chemistry (2013), 78 (19), 9689-9714CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
The scope of palladium-catalyzed, auxiliary-assisted direct arylation and alkylation of sp2 and sp3 C-H bonds of amine and carboxylic acid derivs. has been investigated. The method employs a palladium acetate catalyst, substrate, aryl, alkyl, benzyl, or allyl halide, and inorg. base in tert-amyl alc. or water solvent at 100-140 °C. Aryl and alkyl iodides as well as benzyl and allyl bromides are competent reagents in this transformation. The picolinic acid auxiliary is used for amine γ-functionalization, and the 8-aminoquinoline auxiliary is used for carboxylic acid β-functionalization. Some optimization of base, additives, and solvent is required for achieving best results.
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(c) Daugulis, O.; Roane, J.; Tran, L. D. Bidentate, Monoanionic Auxiliary-Directed Functionalization of Carbon–Hydrogen Bonds. Acc. Chem. Res. 2015, 48, 1053– 1064, DOI: 10.1021/ar5004626
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2c
Bidentate, Monoanionic Auxiliary-Directed Functionalization of Carbon-Hydrogen Bonds
Daugulis, Olafs; Roane, James; Tran, Ly Dieu
Accounts of Chemical Research (2015), 48 (4), 1053-1064CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
A review. In recent years, carbon-hydrogen bond functionalization has evolved from an organometallic curiosity to a tool used in mainstream applications in the synthesis of complex natural products and drugs. The use of C-H bonds as a transformable functional group is advantageous because these bonds are the most abundant functionality in org. mols. One-step conversion of these bonds to the desired functionality shortens synthetic pathways, saving reagents, solvents, and labor. Less chem. waste is generated as well, showing that this chem. is environmentally beneficial. This Account describes the development and use of bidentate, monoanionic auxiliaries for transition-metal-catalyzed C-H bond functionalization reactions. The chem. was initially developed to overcome the limitations with palladium-catalyzed C-H bond functionalization assisted by monodentate directing groups. By the use of electron-rich bidentate directing groups, functionalization of unactivated sp3 C-H bonds under palladium catalysis has been developed. Furthermore, a no. of abundant base-metal complexes catalyze functionalization of sp2 C-H bonds. At this point, aminoquinoline, picolinic acid, and related compds. are among the most used and versatile directing moieties in C-H bond functionalization chem. These groups facilitate catalytic functionalization of sp2 and sp3 C-H bonds by iron, cobalt, nickel, copper, ruthenium, rhodium, and palladium complexes. Exceptionally general reactivity is obsd., enabling, among other transformations, direct arylation, alkylation, fluorination, sulfenylation, amination, etherification, carbonylation, and alkenylation of carbon-hydrogen bonds. The versatility of these auxiliaries can be attributed to the following factors. First, they are capable of stabilizing high oxidn. states of transition metals, thereby facilitating the C-H bond functionalization step. Second, the directing groups can be removed, enabling their use in synthesis and functionalization of natural products and medicinally relevant substances. While the development of these directing groups presents a significant advance, several limitations of this methodol. are apparent. The use of expensive second-row transition metal catalysts is still required for efficient sp3 C-H bond functionalization. Furthermore, the need to install and subsequently remove the relatively expensive directing group is a disadvantage.
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For reviews on chelation-assisted C–H functionalization, see:
(a) Rouquet, G.; Chatani, N. Catalytic Functionalization of C(sp2)–H and C(sp3)–H Bonds by Using Bidentate Directing Groups. Angew. Chem., Int. Ed. 2013, 52, 11726– 11743, DOI: 10.1002/anie.201301451
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3a
Catalytic functionalization of C(sp2)-H and C(sp3)-H bonds by using bidentate directing groups
Rouquet, Guy; Chatani, Naoto
Angewandte Chemie, International Edition (2013), 52 (45), 11726-11743CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. C-H bonds are ubiquitous in org. compds. It would, therefore, appear that direct functionalization of substrates by activation of C-H bonds would eliminate the multiple steps and limitations assocd. with the prepn. of functionalized starting materials. Regioselectivity is an important issue because org. mols. can contain a wide variety of C-H bonds. The use of a directing group can largely overcome the issue of regiocontrol by allowing the catalyst to come into proximity with the targeted C-H bonds. A wide variety of functional groups have been evaluated for use as directing groups in the transformation of C-H bonds. In 2005, Daugulis reported the arylation of unactivated C(sp3)-H bonds by using 8-aminoquinoline and picolinamide as bidentate directing groups, with Pd(OAc)2 as the catalyst. Encouraged by these promising results, a no. of transformations of C-H bonds have since been developed by using systems based on bidentate directing groups. In this review, recent advances in this area are discussed.
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(b) Rit, R. K.; Yadav, M. R.; Ghosh, K.; Sahoo, A. K. Reusable directing groups [8-aminoquinoline, picolinamide, sulfoximine] in C(sp3)–H bond activation: present and future. Tetrahedron 2015, 71, 4450– 4459, DOI: 10.1016/j.tet.2015.03.085
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Reusable directing groups [8-aminoquinoline, picolinamide, sulfoximine] in C(sp3)-H bond activation: present and future
Rit, Raja K.; Yadav, M. Ramu; Ghosh, Koushik; Sahoo, Akhila K.
Tetrahedron (2015), 71 (26-27), 4450-4459CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)
A review. This report briefly discusses the reusable directing group assisted functionalization of unactivated remote alkyl C-H bonds and their synthetic potential in org. chem. The challenges involved for the functionalization of inert alkyl C-H bonds is highlighted. With the strong impact of C-H activation, we believe this report would boost researchers unraveling novel methods for the chemo-, regio-, and stereoselective activation of unbiased C(sp3)-H bonds and their potential utility for the rapid synthesis of complex mol. entities.
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(c) Yang, X.; Shan, G.; Wang, L.; Rao, Y. Recent advances in transition metal (Pd, Ni)-catalyzed C(sp3)–H bond activation with bidentate directing groups. Tetrahedron Lett. 2016, 57, 819– 836, DOI: 10.1016/j.tetlet.2016.01.009
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3c
Recent advances in transition metal (Pd, Ni)-catalyzed C(sp3)-H bond activation with bidentate directing groups
Yang, Xinglin; Shan, Gang; Wang, Liguo; Rao, Yu
Tetrahedron Letters (2016), 57 (8), 819-836CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
A review with refs. In recent years, transition metal-catalyzed C(sp3)-H functionalization has gradually emerged as a practical and powerful tool to prep. highly valuable chems. In this mini-review, we will give some examples to cover recent research advances on transition-metal (Pd, Ni) catalyzed C(sp3)-H functionalization via bidentate directing group coordination. Different bidentate directing groups will be discussed. As the whole field of transition metal-catalyzed C(sp3)-H functionalization keeps moving forward, more synthetically useful chemo-, regio-, diastereo-, and enantioselective reactions catalyzed by transition-metal with bidentate directing group coordination will be discovered in the future and this promising and attractive strategy will play a more crit. role in modern org. synthesis.
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(d) He, R.; Huang, Z.-T.; Zheng, Q.-Y.; Wang, C. Isoquinoline skeleton synthesis via chelation-assisted C–H activation. Tetrahedron Lett. 2014, 55, 5705– 5713, DOI: 10.1016/j.tetlet.2014.08.077
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3d
Isoquinoline skeleton synthesis via chelation-assisted C-H activation
He, Ruoyu; Huang, Zhi-Tang; Zheng, Qi-Yu; Wang, Congyang
Tetrahedron Letters (2014), 55 (42), 5705-5713CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
A review. Transition metal-catalyzed isoquinoline synthesis that profits from the strategy of chelation-assisted C-H activation has flourished over the past decade. By virtue of the directed C-H bond cleavage of imines, amines, amidines, oximes, hydroximoyl halides, hydrazones, or azines, diverse isoquinoline derivs. have been accessed from alkynes, conjugated dienes, or diazo compds. under the catalysis of rhodium, ruthenium, palladium, nickel, or manganese. This digest summarizes the annulation reactions via chelation-assisted C-H activation leading to isoquinolines, isoquinolinium salts, or isoquinoline N-oxides.
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For reviews on Ni-catalyzed C–H functionalization, see:
(a) Tasker, S. Z.; Standley, E. A.; Jamison, T. F. Recent advances in homogeneous nickel catalysis. Nature 2014, 509, 299– 309, DOI: 10.1038/nature13274
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4a
Recent advances in homogeneous nickel catalysis
Tasker, Sarah Z.; Standley, Eric A.; Jamison, Timothy F.
Nature (London, United Kingdom) (2014), 509 (7500), 299-309CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
A review. Tremendous advances have been made in nickel catalysis over the past decade. Several key properties of nickel, such as facile oxidative addn. and ready access to multiple oxidn. states, have allowed the development of a broad range of innovative reactions. In recent years, these properties have been increasingly understood and used to perform transformations long considered exceptionally challenging. Here we discuss some of the most recent and significant developments in homogeneous nickel catalysis, with an emphasis on both synthetic outcome and mechanism.
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(b) Chatani, N. Nickel-Catalyzed C–H Bond Functionalization Utilizing an N,N′-Bidentate Directing Group. Top. Organomet. Chem. 2016, 56, 19– 46
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Nickel-catalyzed C-H bond functionalization utilizing an N,N'-bidentate directing group
Chatani, Naoto
Topics in Organometallic Chemistry (2016), 56 (C-H Bond Activation and Catalytic Functionalization II), 19-46CODEN: TORCFV; ISSN:1616-8534. (Springer GmbH)
This review discusses the use of nickel catalysts and N,N'-bidentate directing groups, such as 2-pyridinylmethylamine, 8-aminoquinoline, and derivs. thereof, which constitute a powerful combination for the chelation-assisted functionalization of C-H bonds.
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(c) Aihara, Y.; Wuelbern, J.; Chatani, N. The Nickel(II)-Catalyzed Direct Benzylation, Allylation, Alkylation, and Methylation of CH Bonds in Aromatic Amides Containing an 8-Aminoquinoline Moiety as the Directing Group. Bull. Chem. Soc. Jpn. 2015, 88, 438– 446, DOI: 10.1246/bcsj.20140387
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4c
The nickel(II)-catalyzed direct benzylation, allylation, alkylation, and methylation of C-H bonds in aromatic amides containing an 8-aminoquinoline moiety as the directing group
Aihara, Yoshinori; Wuelbern, Jendrik; Chatani, Naoto
Bulletin of the Chemical Society of Japan (2015), 88 (3), 438-446CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)
Direct alkylation via the cleavage of the ortho C-H bonds by a nickel-catalyzed reaction of arom. amides contg. an 8-aminoquinoline moiety as the directing group with alkyl halides is reported. Various alkyl halides, including benzyl, allyl, alkyl, and Me halides (or pseudo halides) participate as electrophilic coupling partners. The reaction shows a high functional group compatibility. The reaction proceeds in a highly regioselective manner at the less hindered C-H bonds in the reaction of meta-substituted arom. amides, irresp. of the electronic nature of the substituent. The mechanism responsible for the C-H alkylation reaction is discussed based on the results obtained in a variety of mechanistic expts.
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(d) Castro, L. C. M.; Chatani, N. Nickel Catalysts/N,N′-Bidentate Directing Groups: An Excellent Partnership in Directed C–H Activation Reactions. Chem. Lett. 2015, 44, 410– 421, DOI: 10.1246/cl.150024
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4d
Nickel catalysts/N,N'-bidentate directing groups: an excellent partnership in directed C-H activation reactions
Castro, Luis C. Misal; Chatani, Naoto
Chemistry Letters (2015), 44 (4), 410-421CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
A review. This review focuses on chelation-assisted regioselective C-H activation with C-C or/and C-N bond formation using Nickel(0) or -(II) as the catalysts, where bidentate directing groups play a key role in the successful transformation. A 2-pyridinylmethylamine or an 8-aminoquinoline moiety are the more powerful auxiliaries among the directing groups examd.
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(e) Cai, X.; Xie, B. Recent advances in nickel-catalyzed C–H bond functionalized reactions. ARKIVOC 2015, i, 184, DOI: 10.3998/ark.5550190.p008.915
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(f) Yamaguchi, J.; Muto, K.; Itami, K. Nickel-Catalyzed Aromatic C-H Functionalization. Top. Curr. Chem. 2016, 374, 55, DOI: 10.1007/s41061-016-0053-z
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Nickel-Catalyzed Aromatic C-H Functionalization
Yamaguchi Junichiro; Muto Kei; Itami Kenichiro; Itami Kenichiro
Topics in current chemistry (Cham) (2016), 374 (4), 55 ISSN:2365-0869.
Catalytic C-H functionalization using transition metals has received significant interest from organic chemists because it provides a new strategy to construct carbon-carbon bonds and carbon-heteroatom bonds in highly functionalized, complex molecules without pre-functionalization. Recently, inexpensive catalysts based on transition metals such as copper, iron, cobalt, and nickel have seen more use in the laboratory. This review describes recent progress in nickel-catalyzed aromatic C-H functionalization reactions classified by reaction types and reaction partners. Furthermore, some reaction mechanisms are described and cutting-edge syntheses of natural products and pharmaceuticals using nickel-catalyzed aromatic C-H functionalization are presented.
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(g) Yamaguchi, J.; Muto, K.; Itami, K. Recent Progress in Nickel-Catalyzed Biaryl Coupling. Eur. J. Org. Chem. 2013, 19– 30, DOI: 10.1002/ejoc.201200914
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Recent progress in nickel-catalyzed biaryl coupling
Yamaguchi, Junichiro; Muto, Kei; Itami, Kenichiro
European Journal of Organic Chemistry (2013), 2013 (1), 19-30CODEN: EJOCFK; ISSN:1099-0690. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review. Nickel catalysis for biaryl coupling reactions has received significant attention as a less expensive and less toxic alternative to "std." palladium catalysis. Here we describe recent developments in nickel-catalyzed biaryl coupling methodol., along with mechanistic studies and applications. In particular we focus on nickel-catalyzed coupling reactions in which "unreactive" bonds such as C-H, C-O, and C-C bonds are converted into biaryl moieties.
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(h) Khan, M. S.; Haque, A.; Al-Suti, M. K.; Raithby, P. R. Recent advances in the application of group-10 transition metal based catalysts in C-H activation and functionalization. J. Organomet. Chem. 2015, 793, 114– 133, DOI: 10.1016/j.jorganchem.2015.03.023
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4h
Recent advances in the application of group-10 transition metal based catalysts in C-H activation and functionalization
Khan, Muhammad S.; Haque, Ashanul; Al-Suti, Mohammed K.; Raithby, Paul R.
Journal of Organometallic Chemistry (2015), 793 (), 114-133CODEN: JORCAI; ISSN:0022-328X. (Elsevier B.V.)
A review. The importance of C-H bond activation in a simple mol. to form a mol. with enhanced functionality can be easily understood from a study of biol. processes at a mol. level where, for example, a specific enzyme selectively activates a chem. inert C-H bond and functionalizes it to a useful product. This strategy is now being used for large scale industrial processes and has both social and environmental benefits. C-H bond functionalization is also of major importance in catalysis because of the possibility of constructing complex structural motifs from relatively simple precursors. However, functionalization of a chem. inert C-H bond needs specific catalysts or reaction conditions that can selectively activate a particular C-H bond, leaving others intact. To achieve this target, various metal catalyzed or mediated reactions have been employed. Keeping the growing importance of this emerging field in mind, we now present recent advances in the field of C-H activation and functionalization using group 10 transition metal catalysts. Attempts have also been made to discuss the future of group 10 transition metals in catalysis.
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(i) Johnson, S. A. Nickel complexes for catalytic C–H bond functionalization. Dalton Trans. 2015, 44, 10905– 10913, DOI: 10.1039/C5DT00032G
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4i
Nickel complexes for catalytic C-H bond functionalization
Johnson, S. A.
Dalton Transactions (2015), 44 (24), 10905-10913CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
A review. The direct catalytic functionalization of traditionally unreactive C-H bonds is an atom-economic transformation that has become increasingly important and commonplace in synthetic applications. In general, 2nd and 3rd row transition metal complexes are used as catalysts in these reactions, whereas the less costly and more abundant 1st row metal complexes have limited utility. This Perspective article summarizes progress from lab. towards understanding the fundamental issues that complicate the use of Ni complexes for catalytic C-H bond functionalization, as well as approaches to overcoming these limitations. In practice Ni complexes can functionalize C-H bonds by processes that, to date, were not obsd. with the heavier metals. An example is provided by the catalytic stannylation of C-H bonds with tributylvinyltin, Bu3SnCH=CH2, which produces ethylene as a byproduct.
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(a) Davies, D. L.; Donald, S. M. A.; Macgregor, S. A. Computational Study of the Mechanism of Cyclometalation by Palladium Acetate. J. Am. Chem. Soc. 2005, 127, 13754– 13755, DOI: 10.1021/ja052047w
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5a
Computational Study of the Mechanism of Cyclometalation by Palladium Acetate
Davies, David L.; Donald, Steven M. A.; Macgregor, Stuart A.
Journal of the American Chemical Society (2005), 127 (40), 13754-13755CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Various mechanisms for the cyclometalation of dimethylbenzylamine by Pd acetate were studied by DFT calcns. Contrary to previous suggestions, the rate-limiting step is the electrophilic attack of the Pd on an ortho arene C-H bond to form an agostic complex rather than a Wheland intermediate. The cyclometalated product is then formed by intramol. deprotonation by acetate via a six-membered transition state; this step has almost no activation barrier.
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(b) Lapointe, D.; Fagnou, K. Computational Study of the Mechanism of Cyclometalation by Palladium Acetate. Chem. Lett. 2010, 39, 1118– 1126, DOI: 10.1246/cl.2010.1118
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(c) Lafrance, M.; Gorelsky, S. I.; Fagnou, K. High-Yielding Palladium-Catalyzed Intramolecular Alkane Arylation: Reaction Development and Mechanistic Studies. J. Am. Chem. Soc. 2007, 129, 14570– 14571, DOI: 10.1021/ja076588s
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5c
High-Yielding Palladium-Catalyzed Intramolecular Alkane Arylation: Reaction Development and Mechanistic Studies
Lafrance, Marc; Gorelsky, Serge I.; Fagnou, Keith
Journal of the American Chemical Society (2007), 129 (47), 14570-14571CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Palladium-catalyzed alkane arylation reactions with aryl halides are described for the prepn. of 2,2-dialkyl-dihydrobenzofuran substrates. These reactions occur in excellent yield and very high selectivity for the formation of one sole product arising from a reaction at nearby Me groups. Mechanistic and computational studies point to the involvement of a concerted, inner-sphere palladation-deprotonation pathway that is enabled by the presence of three-center agostic interactions at the transition state. This mechanism accurately predicts the exptl. obsd. kinetic isotope effect as well as the site selectivity and should be useful in the design of new reactions and catalysts.
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(d) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. Analysis of the Concerted Metalation-Deprotonation Mechanism in Palladium-Catalyzed Direct Arylation Across a Broad Range of Aromatic Substrates. J. Am. Chem. Soc. 2008, 130, 10848– 10849, DOI: 10.1021/ja802533u
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5d
Analysis of the Concerted Metalation-Deprotonation Mechanism in Palladium-Catalyzed Direct Arylation Across a Broad Range of Aromatic Substrates
Gorelsky, Serge I.; Lapointe, David; Fagnou, Keith
Journal of the American Chemical Society (2008), 130 (33), 10848-10849CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The concerted metalation-deprotonation mechanism predicts relative reactivity and regioselectivity for a diverse set of arenes spanning the entire spectrum of known palladium-catalyzed direct arylation coupling partners. An anal. following an active strain model provides a more complete portrayal of the important arene/catalyst parameters leading to a successful coupling. The breadth of arenes whose reactivity can be predicted by the CMD mechanism indicates that it may be far more widespread than previously imagined.
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(e) Guihaumé, J.; Clot, E.; Eisenstein, O.; Perutz, R. N. Importance of palladium–carbon bond energies in direct arylation of polyfluorinated benzenes. Dalton Trans. 2010, 39, 10510– 10519, DOI: 10.1039/c0dt00296h
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5e
Importance of palladium-carbon bond energies in direct arylation of polyfluorinated benzenes
Guihaume, Julie; Clot, Eric; Eisenstein, Odile; Perutz, Robin N.
Dalton Transactions (2010), 39 (43), 10510-10519CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
Fagnou et al. reported direct arylation reactions that use palladium catalysts to couple Ar1-X to Ar2-H with the aid of a coordinated base. These reactions are particularly favorable for polyfluorinated arenes Ar2-H (see S. I. Gorelsky, D. Lapointe and K. Fagnou, J. Am. Chem. Soc. 2008, 130, 10848). In this paper, we show by means of a DFT anal. how the energetics and activation energies vary with fluorine substitution and examine the structures of intermediates and transition states. The reactant is modelled by Pd(OAc)(Ph)(PMe3)(DMA) (DMA = dimethylacetamide). The sequence consists of (a) replacement of DMA by arene, (b) Concerted Deprotonation Metalation (CMD), (c) decoordination of AcOH, (d) reductive elimination of biaryl. Many of the variations are dominated by the no. of fluorine substituents ortho to the C-H bond and fall into three groups labeled accordingly: Set0Fo, Set1Fo, and Set2Fo. In the first step a coordinated solvent is replaced by the arene. The arenes of Set0Fo and Set1Fo coordinate in a conventional η2-CH:CH mode, whereas the arenes of Set2Fo coordinate in an η1-CH mode assisted by an O···H-C hydrogen bond from the coordinated acetate. Both the energy barriers to CMD and the product energies fall into the three typical sets with the highest barrier and highest product energy being for Set0Fo. They correlate more satisfactorily with the variations in Pd-C bond energies than with the C-H acidities. The barriers to reductive elimination from Pd(Ph)(ArF)(PMe3)(AcOH) increase systematically from Set0Fo to Set2Fo as the Pd-C bond becomes stronger in a regular fashion from Set0Fo to Set2Fo. Again there is a strong correlation between the energy barriers to reductive elimination and the Pd-C bond energies. It is found overall that the key aspects of the reactions are: (a) the lowering of the energy of the CMD step by the ortho fluorine substituents, (b) the regioselective activation of C-H bonds ortho to fluorine which is also detd. at the CMD step, (c) the decoordination of AcOH, which maintains the transition state for reductive elimination at low Gibbs free energy. The presence of fluorine increases the effectiveness of the reaction in the sense of points a and b via the increasing strength of the palladium-carbon bond.
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(f) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. Analysis of the Palladium-Catalyzed (Aromatic)C–H Bond Metalation–Deprotonation Mechanism Spanning the Entire Spectrum of Arenes. J. Org. Chem. 2012, 77, 658– 668, DOI: 10.1021/jo202342q
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5f
Analysis of the Palladium-Catalyzed (Aromatic)C-H Bond Metalation-Deprotonation Mechanism Spanning the Entire Spectrum of Arenes
Gorelsky, Serge I.; Lapointe, David; Fagnou, Keith
Journal of Organic Chemistry (2012), 77 (1), 658-668CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
A comprehensive understanding of the C-H bond cleavage step by the concerted metalation-deprotonation (CMD) pathway is important in further development of cross-coupling reactions using different catalysts. Distortion-interaction anal. of the C-H bond cleavage over a wide range of (hetero)aroms. has been performed in an attempt to quantify the various contributions to the CMD transition state (TS). The (hetero)aroms. evaluated were divided in different categories to allow an easier understanding of their reactivity and to quantify activation characteristics of different arene substituents. The CMD pathway to the C-H bond cleavage for different classes of arenes is also presented, including the formation of pre-CMD intermediates and the anal. of bonding interactions in TS structures. The effects of remote C2 substituents on the reactivity of thiophenes were evaluated computationally and were corroborated exptl. with competition studies. We show that nucleophilicity of thiophenes, evaluated by Hammett σp parameters, correlates with each of the distortion-interaction parameters. In the final part of this manuscript, we set the initial equations that can assist in the development of predictive guidelines for the functionalization of C-H bonds catalyzed by transition metal catalysts.
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(g) Petit, A.; Flygare, J.; Miller, A. T.; Winkel, G.; Ess, D. H. Transition-State Metal Aryl Bond Stability Determines Regioselectivity in Palladium Acetate Mediated C–H Bond Activation of Heteroarenes. Org. Lett. 2012, 14, 3680– 3683, DOI: 10.1021/ol301521n
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5g
Transition-State Metal Aryl Bond Stability Determines Regioselectivity in Palladium Acetate Mediated C-H Bond Activation of Heteroarenes
Petit, Alban; Flygare, Josh; Miller, Alex T.; Winkel, Gerrit; Ess, Daniel H.
Organic Letters (2012), 14 (14), 3680-3683CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
D. functional calcns. reveal that the stability of developing metal aryl bonds in Pd(II)-acetate C-H activation transition states dets. regioselectivity in arene and heteroarene compds. This kinetic-thermodn. connection explains the general preference for activation of the strongest C-H bond and provides the possibility for regioselectivity prediction.
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(h) Dang, Y.; Qu, S.; Nelson, J. W.; Pham, H. D.; Wang, Z.-X.; Wang, X. The Mechanism of a Ligand-Promoted C(sp3)–H Activation and Arylation Reaction via Palladium Catalysis: Theoretical Demonstration of a Pd(II)/Pd(IV) Redox Manifold. J. Am. Chem. Soc. 2015, 137, 2006– 2014, DOI: 10.1021/ja512374g
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5h
The Mechanism of a Ligand-Promoted C(sp3)-H Activation and Arylation Reaction via Palladium Catalysis: Theoretical Demonstration of a Pd(II)/Pd(IV) Redox Manifold
Dang, Yanfeng; Qu, Shuanglin; Nelson, John W.; Pham, Hai D.; Wang, Zhi-Xiang; Wang, Xiaotai
Journal of the American Chemical Society (2015), 137 (5), 2006-2014CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
D. functional theory (DFT) computations (BP86 and M06-L) have been utilized to elucidate the detailed mechanism of a palladium-catalyzed reaction involving pyridine-type nitrogen-donor ligands that significantly expands the scope of C(sp3)-H activation and arylation. The reaction begins with precatalyst initiation, followed by substrate binding to the Pd(II) center through an amidate auxiliary, which directs the ensuing bicarbonate-assisted C(sp3)-H bond activation producing five-membered-ring cyclopalladate(II) intermediates. These Pd(II) complexes further undergo oxidative addn. with iodobenzene to form Pd(IV) complexes, which proceed by reductive C-C elimination/coupling to give final products of arylation. The base-assisted C(sp3)-H bond cleavage is found to be the rate-detg. step, which involves hydrogen bond interactions. The mechanism unravels the intimate involvement of the added 2-picoline ligand in every phase of the reaction, explains the isolation of the cyclopalladate intermediates, agrees with the obsd. kinetic hydrogen isotope effect, and demonstrates the Pd(II)/Pd(IV) redox manifold.
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(i) Dang, Y.; Deng, X.; Guo, J.; Song, C.; Hu, W.; Wang, Z.-X. Unveiling Secrets of Overcoming the “Heteroatom Problem” in Palladium-Catalyzed Aerobic C–H Functionalization of Heterocycles: A DFT Mechanistic Study. J. Am. Chem. Soc. 2016, 138, 2712– 2723, DOI: 10.1021/jacs.5b12112
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5i
Unveiling Secrets of Overcoming the "Heteroatom Problem" in Palladium-Catalyzed Aerobic C-H Functionalization of Heterocycles: A DFT Mechanistic Study
Dang, Yanfeng; Deng, Xi; Guo, Jiandong; Song, Chunyu; Hu, Wenping; Wang, Zhi-Xiang
Journal of the American Chemical Society (2016), 138 (8), 2712-2723CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Directed C-H functionalization of heterocycles through an exocyclic directing group (DG) is challenging due to the interference of the endocyclic heteroatom(s). Recently, the heteroatom problem was circumvented with the development of the protection-free Pd-catalyzed aerobic C-H functionalization of heterocycles guided by an exocyclic CONHOMe DG. The authors herein provide DFT mechanistic insights to facilitate the expansion of the strategy. The transformation proceeds as follows. First, the Pd2(dba)3 precursor interacts with t-BuNC (L, one of the substrates) and O2 to form the L2Pd(II)-η2-O2 peroxopalladium(II) species that can selectively oxidize N-methoxy amide (e.g., PyCONHOMe) substrate, giving an active L2Pd(II)X2 (X = PyCONOMe) species and releasing H2O2. After t-BuNC ligand migratory insertion followed by a 1,3-acyl migration and assocn. with another t-BuNC, L2Pd(II)X2 converts to a more stable C-amidinyl L2Pd(II)XX' (X' = PyCON(t-Bu)C=NOMe) species. Finally, L2Pd(II)XX' undergoes C-H activation and C-C reductive elimination, affording the product. The C-H activation is the rate-detg. step. The success of the strategy has three origins: (i) the N-methoxy amide DG can be easily oxidized in situ to generate the active L2Pd(II)X2 species via the oxidase pathway, thus preventing the destructive oxygenase pathway leading to stable t-BuNCO or the O-bridged dimeric Pd(II) species. The methoxy group in this amide DG greatly facilitates the oxidase pathway, and the tautomerization of N-methoxy amide to its imidic acid tautomer makes the oxidn. of the substrate even easier. (ii) The X group in L2Pd(II)X2 can serve as an internal base to promote the C-H activation via CMD (concerted metalation-deprotonation) mechanism. (iii) The strong coordination ability of t-BuNC substrate/ligand suppresses the conventional cyclopalladation pathway enabled by the coordination of an endocyclic heteroatom to the Pd-center.
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(j) Davies, D. L.; Macgregor, S. A.; McMullin, C. L. Computational Studies of Carboxylate-Assisted C–H Activation and Functionalization at Group 8–10 Transition Metal Centers. Chem. Rev. 2017, 117, 8649– 8709, DOI: 10.1021/acs.chemrev.6b00839
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5j
Computational Studies of Carboxylate-Assisted C-H Activation and Functionalization at Group 8-10 Transition Metal Centers
Davies, David L.; Macgregor, Stuart A.; McMullin, Claire L.
Chemical Reviews (Washington, DC, United States) (2017), 117 (13), 8649-8709CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
Computational studies on carboxylate-assisted C-H activation and functionalization at group 8-10 transition metal centers are reviewed. This Review is organized by metal and will cover work published from late 2009 until mid-2016. A brief overview of computational work prior to 2010 is also provided, and this outlines the understanding of carboxylate-assisted C-H activation in terms of the "ambiphilic metal-ligand assistance" (AMLA) and "concerted metalation deprotonation" (CMD) concepts. Computational studies are then surveyed in terms of the nature of the C-H bond being activated (C(sp2)-H or C(sp3)-H), the nature of the process involved (intramol. with a directing group or intermol.), and the context (stoichiometric C-H activation or within a variety of catalytic processes). This Review aims to emphasize the connection between computation and expt. and to highlight the contribution of computational chem. to our understanding of catalytic C-H functionalization based on carboxylate-assisted C-H activation. Some opportunities where the interplay between computation and expt. may contribute further to the areas of catalytic C-H functionalization and applied computational chem. are identified.
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(k) García-Cuadrado, D.; Braga, A. A. C.; Maseras, F.; Echavarren, A. M. Proton Abstraction Mechanism for the Palladium-Catalyzed Intramolecular Arylation. J. Am. Chem. Soc. 2006, 128, 1066– 1067, DOI: 10.1021/ja056165v
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5k
Proton Abstraction Mechanism for the Palladium-Catalyzed Intramolecular Arylation
Garcia-Cuadrado, Domingo; Braga, Ataualpa A. C.; Maseras, Feliu; Echavarren, Antonio M.
Journal of the American Chemical Society (2006), 128 (4), 1066-1067CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Under the usual conditions, the Pd-catalyzed arylation does not involve an electrophilic arom. substitution reaction. On the basis of DFT calcns., we propose a mechanism for the Pd-catalyzed arylation that involves a proton abstraction by a carbonate or related ligand and that provides a satisfactory explanation for the exptl. data.
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(l) Lafrance, M.; Rowley, C. N.; Woo, T. K.; Fagnou, K. Catalytic Intermolecular Direct Arylation of Perfluorobenzenes. J. Am. Chem. Soc. 2006, 128, 8754– 8756, DOI: 10.1021/ja062509l
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5l
Catalytic Intermolecular Direct Arylation of Perfluorobenzenes
Lafrance, Marc; Rowley, Christopher N.; Woo, Tom K.; Fagnou, Keith
Journal of the American Chemical Society (2006), 128 (27), 8754-8756CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Penta-, tetra-, tri-, and difluorobenzenes undergo direct arylation with a wide range of aryl halides in high yield. Inverse reactivity is obsd. compared to the common electrophilic arom. substitution pathway since electron-deficient, C-H acidic arenes react preferentially. Computational studies indicate that C-H bond cleavage occurs via a concerted carbon-palladium and carbon-hydrogen bond cleaving event involving a carbonate or a bromide ligand. The reactions are rapid, require only a slight excess of the perfluoroarene reagent, and utilize com. available, air-stable catalyst precursors.
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(m) Pascual, S.; Mendoza, P.; Braga, A. A. C.; Maseras, F.; Echavarren, A. M. Bidentate phosphines as ligands in the palladium-catalyzed intramolecular arylation: the intermolecular base-assisted proton abstraction mechanism. Tetrahedron 2008, 64, 6021– 6029, DOI: 10.1016/j.tet.2008.01.056
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5m
Bidentate phosphines as ligands in the palladium-catalyzed intramolecular arylation: the intermolecular base-assisted proton abstraction mechanism
Pascual, Sergio; de Mendoza, Paula; Braga, Ataualpa A. C.; Maseras, Feliu; Echavarren, Antonio M.
Tetrahedron (2008), 64 (26), 6021-6029CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)
The palladium-catalyzed arylation of aryl bromides can be carried out in the presence of bidentate phosphines, such as dppm, dppe, dppf, and Xantphos under mild conditions. The exptl. results and the DFT calcns. fully support for this reaction a mechanism proceeding by an intermol. proton abstraction.
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(n) Kefalidis, C. E.; Baudoin, O.; Clot, E. DFT study of the mechanism of benzocyclobutene formation by palladium-catalysed C(sp3)–H activation: role of the nature of the base and the phosphine. Dalton Trans. 2010, 39, 10528– 10535, DOI: 10.1039/c0dt00578a
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5n
DFT study of the mechanism of benzocyclobutene formation by palladium-catalysed C(sp3)-H activation: role of the nature of the base and the phosphine
Kefalidis, Christos E.; Baudoin, Olivier; Clot, Eric
Dalton Transactions (2010), 39 (43), 10528-10535CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
DFT(B3PW91) calcns. of the mechanism of the intramol. C(sp3)-H arylation of 2-bromo-tert-butylbenzene to form benzocyclobutene catalyzed by Pd(PR3) (R = Me, tBu) and a base (acetate, bicarbonate, carbonate) show that the preferred mechanism is highly dependent on the nature of the phosphine and the base used in the calcns. With the exptl. reagents (PtBu3 and carbonate) the rate-detg. step is C-H activation with the base coordinated trans to the C-H bond. An agostic interaction of a geminal C-H bond with respect to the bond to be cleaved induces a lowering of the activation barrier.
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(o) Korenaga, T.; Suzuki, N.; Sueda, M.; Shimada, K. Ligand effect on direct arylation by CMD process. J. Organomet. Chem. 2015, 780, 63– 69, DOI: 10.1016/j.jorganchem.2014.12.017
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5o
Ligand effect on direct arylation by CMD process
Korenaga, Toshinobu; Suzuki, Noriki; Sueda, Masayoshi; Shimada, Kazuaki
Journal of Organometallic Chemistry (2015), 780 (), 63-69CODEN: JORCAI; ISSN:0022-328X. (Elsevier B.V.)
The ligand effect of electron-poor phosphines in the concerted metalation-deprotonation (CMD) process for intramol. direct arylation was exptl. and theor. demonstrated. The ligand acceleration effect (LAE) for the intramol. direct arylation of 1-bromo-2-(phenoxymethyl)benzene increased in the following order: P(BFPy)3 > P{3,5-(CF3)2-C6H3}3 > PCy3 > P(3,4,5-F3-C6H2)3 > P(4-F-C6H4)3 = PPh3 » P(C6F5)3. The use of highly electron-poor P(BFPy)3 allowed the catalyst loading to be decreased up to 0.01 mol%. The LAE is roughly proportional to the electronic effect of the phosphine ligand. The LAE was not obsd. in the case of P(C6F5)3 because of its lack of coordination ability for Pd(OAc)2, as confirmed by 31P NMR spectroscopy. The donating PCy3 ligand showed a higher LAE than PPh3. The relative activation free energies (ΔG≠) of the CMD process calcd. by the d. functional theory (DFT) at the M06-2X/6-31G(d) level with LANL2DZ showed the same trend as the exptl. results. The LAE in CMD was further evaluated by DFT calcns. using two approaches: (1) fragment energy anal. and (2) evaluation of NBO deletion energy in transition states in CMD. The results of the first technique indicated that the conformational change in PCy3 results in increase of activation energy (ΔE≠) in compared with PAr3 systems. The use of the second technique clarified that the highly electron-poor P(BFPy)3 ligand stabilized the CAr→Pd interaction and the electron-donating PCy3 stabilized the O→H···CAr interaction in the transition state in CMD.
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(p) Holstein, P. M.; Vogler, M.; Larini, P.; Pilet, G.; Clot, E.; Baudoin, O. Efficient Pd0-Catalyzed Asymmetric Activation of Primary and Secondary C–H Bonds Enabled by Modular Binepine Ligands and Carbonate Bases. ACS Catal. 2015, 5, 4300– 4308, DOI: 10.1021/acscatal.5b00898
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5p
Efficient Pd0-Catalyzed Asymmetric Activation of Primary and Secondary C-H Bonds Enabled by Modular Binepine Ligands and Carbonate Bases
Holstein, Philipp M.; Vogler, Maria; Larini, Paolo; Pilet, Guillaume; Clot, Eric; Baudoin, Olivier
ACS Catalysis (2015), 5 (7), 4300-4308CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
New binepine ligands were synthesized, and characterized and induce high diastereo- and enantioselectivity in the intramol. arylation of primary and secondary C(sp3)-H bonds, giving rise to fused cyclopentanes. The ligands were obtained as bench-stable phosphonium tetrafluoroborate salts that can be directly employed in catalysis. A ferrocenyl P-substituent on the ligand allows achievement of high stereoselectivities in combination with potassium carbonate for the arylation of primary C-H bonds under unprecedentedly low temp. (90 °C) and catalyst loading (1-2 mol % Pd/2-3 mol % ligand). Using a base-free precatalyst, carbonate is the active base and to provide higher stereoselectivities than acetate and pivalate. The more difficult arylation of secondary C-H bonds could also be achieved and required fine-tuning of the ligand structure and the carbonate countercation. This method gave fused tricyclic products contg. three adjacent stereocenters as single diastereoisomers and with moderate to high enantioselectivity. Exptl. data indicated that the enantiodetermining C-H activation step involves a monoligated species. DFT (PBE0-D3) calcns. were performed with a prototypical binepine ligand to understand the origin of the enantioselectivity. The preference for the major enantiomer was traced to the establishment of a more efficient network of weak attractive interactions between the phosphine ligand and the substrate.
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Gensch, T.; Hopkinson, M. N.; Glorius, F.; Wencel-Delord, J. Mild metal-catalyzed C–H activation: examples and concepts. Chem. Soc. Rev. 2016, 45, 2900– 2936, DOI: 10.1039/C6CS00075D
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6
Mild metal-catalyzed C-H activation: examples and concepts
Gensch, T.; Hopkinson, M. N.; Glorius, F.; Wencel-Delord, J.
Chemical Society Reviews (2016), 45 (10), 2900-2936CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
A review. In this review, the current state of the art that have been made in field of mild C-H activation transformations reported since 2011 that proceed either at or below ambient temp., in the absence of strongly acidic or basic additives or without strong oxidants have been presented. Furthermore, by identifying and discussing the major strategies that have led to these improvements, this review will serve as a useful conceptual overview and inspire the next generation of mild C-H transformations.
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Perutz, R. N.; Sabo-Etienne, S. The σ-CAM Mechanism: σ-Complexes as the Basis of σ-Bond Metathesis at Late-Transition-Metal Centers. Angew. Chem., Int. Ed. 2007, 46, 2578– 2592, DOI: 10.1002/anie.200603224
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7
The σ-CAM mechanism: σ complexes as the basis of σ-bond metathesis at late-transition-metal centers
Perutz, Robin N.; Sabo-Etienne, Sylviane
Angewandte Chemie, International Edition (2007), 46 (15), 2578-2592CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A review of σ complexes particularly with silane and borane ligands, in which a σ-H-E bond (E = H, B, Si, C) acts as a two-electron donor to the metal center is presented. Clues that it is possible to interconvert σ ligands without a change in oxidn. state derive from C-H activation reactions effecting isotope exchange and from dynamic rearrangements of σ-complexes (see frontispiece). Through these pathways, metathesis of M-E bonds can occur at late transition metals. This process of σ-complex-assisted metathesis, or σ-CAM, is distinct from the familiar σ-bond metathesis (typical for d0 metals and requiring no intermediate) and from oxidative-reductive elimination mechanisms (inherently requiring intermediates with changed oxidn. states and sometimes involving α complexes). There are examples of σ-CAM mechanisms in catalysis, esp. for alkane borylation and isotope exchange of alkanes. It may also occur in silylation and alkene hydrogenation.
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(a) Guihaumé, J.; Halbert, S.; Eisenstein, O.; Perutz, R. N. Hydrofluoroarylation of Alkynes with Ni Catalysts. C–H Activation via Ligand-to-Ligand Hydrogen Transfer, an Alternative to Oxidative Addition. Organometallics 2012, 31, 1300– 1314, DOI: 10.1021/om2005673
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8a
Hydrofluoroarylation of alkynes with Ni catalysts. C-H activation via ligand-to-ligand hydrogen transfer, an alternative to oxidative addition
Guihaume, Julie; Halbert, Stephanie; Eisenstein, Odile; Perutz, Robin N.
Organometallics (2012), 31 (4), 1300-1314CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
The mechanism of the hydrofluoroarylation of alkynes, RC≡CR, by nickel phosphine complexes, described by Nakao et al., was studied by d. functional theory (DFT) calcns. The oxidative addn. of a C-H bond of partially fluorinated benzenes, C6FnH6-n (n = 0-5) to a Ni(0) phosphine complex is reversible, but the oxidative addn. of a C-F bond yields a stable product via a high-energy barrier. A pathway via the Ni(II) hydride complex is eliminated on the basis of a calcd. H/D kinetic isotope effect (KIE) that does not agree with the measured value. An alternate pathway was detd., using as reactant a Ni(phosphine)(alkyne) complex that is shown to be the major species in the reactive media under the catalytic conditions. This pathway is initiated by arene coordination to the Ni alkyne complex followed by proton transfer from the σ-C-H bond of the coordinated arene to the alkyne as the C-H activation step. Anal. of the charge distribution shows that the alkyne is strongly neg. charged when coordinated to the Ni(phosphine) species, which favors a C-H activation as a proton transfer, similar to that in CMD and AMLA but not previously seen between hydrocarbyl ligands for electron rich metals. The C-H activation step thus represents an example of a general class of mechanism that we term ligand-to-ligand hydrogen transfer (LLHT). The product of this reaction is a nickel(vinyl)(aryl) complex, which rearranges to place the aryl and vinyl groups cis to one another before undergoing reductive elimination of the arylalkene. An anal. of the calcd. turnover frequencies shows that the rate-detg. states that control the energy span are the alkyne complex + free arene and the transition state for the vinyl-aryl complex trans-to-cis rearrangement. The calcd. KIE agrees with the obsd. lack of isotope effect. Anal. of the effects of fluorine substituents shows that the Ni-C(aryl) bond energies control the energy barriers for the arene C-H activation step and the energy spans. A correlation between bond dissocn. energies for the Ni-C(aryl) bond and the arene C-H bond follows the behavior presented previously, in which the effects of ortho fluorine substituents are dominant. Consequently, fluorine substitution of the arene, esp. at the ortho positions, strengthens the Ni-C bond and increases the TOF. The LLHT mechanism described here may also apply to nickel-catalyzed C-H activation reactions with other substrates.
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(b) Tang, S.; Eisenstein, O.; Nakao, Y.; Sakaki, S. Aromatic C–H σ-Bond Activation by Ni0, Pd0, and Pt0 Alkene Complexes: Concerted Oxidative Addition to Metal vs Ligand-to-Ligand H Transfer Mechanism. Organometallics 2017, 36, 2761– 2771, DOI: 10.1021/acs.organomet.7b00256
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8b
Aromatic C-H σ-Bond Activation by Ni0, Pd0, and Pt0 Alkene Complexes: Concerted Oxidative Addition to Metal vs Ligand-to-Ligand H Transfer Mechanism
Tang, Shuwei; Eisenstein, Odile; Nakao, Yoshiaki; Sakaki, Shigeyoshi
Organometallics (2017), 36 (15), 2761-2771CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
C-H σ-bond activation of arene (represented here by benzene) by the Ni0 propene complex Ni0(IMes)(C3H6) (IMes = 1,3-dimesitylimidazol-2-ylidene), which is an important elementary step in Ni-catalyzed hydroarylation of unactivated alkene with arene, was investigated by DFT calcns. In the Ni0 complex, the C-H activation occurs through a ligand-to-ligand H transfer mechanism to yield NiII(IMes)(C3H7)(Ph) (C3H7 = propyl; Ph = phenyl). In Pd0 and Pt0 analogs, the activation occurs through concerted oxidative addn. of the C-H bond to the metal. Anal. of the electron redistribution during the C-H activation highlights the difference between the two mechanisms. In the ligand-to-ligand H transfer, charge transfer (CT) occurs from the metal to the benzene. However, the at. population of the transferring H remains almost const., suggesting that different CT simultaneously occurs from the transferring H to the LUMO of propene. The electron redistribution contrasts significantly with that found for Pd0 and Pt0, in which CT occurs only from the metal to the benzene. Preference for ligand-to-ligand H transfer over concerted oxidative addn. in the Ni0 complex is shown to be due to the smaller at. radius of Ni in comparison to those of Pd and Pt and the smaller NiII-H bond energy relative to the PdII-H and PtII-H energies. Interestingly, the bulky ligand accelerates the ligand-to-ligand H transfer in the Ni0 complex by decreasing the distance between the coordinated benzene and alkene substrates. Thus, the Gibbs activation energy (ΔG°⧺) decreases in the case of cyclic-alkylaminocarbene with bulky substituents (CACC-K3), while the ΔG°⧺ values are similar in X-Phos, IMes, and nonsubstituted cyclic alkylaminocarbene (CAAC-K0). An electron-withdrawing substituent on the arene accelerates the C-H activation by favoring the metal to arene CT.
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(c) Yamazaki, K.; Obata, A.; Sasagawa, A.; Ano, Y.; Chatani, N. Computational Mechanistic Study on the Nickel-Catalyzed C–H/N–H Oxidative Annulation of Aromatic Amides with Alkynes: The Role of the Nickel (0) Ate Complex. Organometallics 2019, 38, 248– 255, DOI: 10.1021/acs.organomet.8b00684
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8c
Computational Mechanistic Study on the Nickel-Catalyzed C-H/N-H Oxidative Annulation of Aromatic Amides with Alkynes: The Role of the Nickel(0) Ate Complex
Yamazaki, Ken; Obata, Atsushi; Sasagawa, Akane; Ano, Yusuke; Chatani, Naoto
Organometallics (2019), 38 (2), 248-255CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
D. functional theory (DFT) was used to unveil intimate mechanistic insights on the monodentate-chelation system that is used in the Ni-catalyzed C-H/N-H oxidative annulation of arom. amides with alkynes, a reaction that was originally reported by our group (Chem Sci. 2017, 8, 6650-6655, DOI: 10.1039/C7SC01750B). The proposed reaction mechanism involves two reaction paths. The initial path is initiated by Ni(II), and the other, the main catalytic cycle, is initiated by Ni(0). Both paths require the presence of a catalytic amt. of KOBut. The results of the DFT studies presented here indicate that the rate-detg. step in the initial Ni(II) system involves a concerted metalation-deprotonation (CMD) mechanism and an anionic Ni(0) ate complex is the key intermediate in the main catalytic cycle. Furthermore, a previously proposed oxidative addn.-alkyne insertion sequence is revised to a ligand-to-ligand hydrogen transfer (LLHT) mechanism, which is the rate-detg. step in the main catalytic cycle. The computed regioselectivity of the asym. alkynes and meta-substituted arom. amides that are produced in such reactions is in good agreement with the exptl. results.
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(a) Shibata, K.; Hasegawa, N.; Fukumoto, Y.; Chatani, N. Ruthenium-Catalyzed Carbonylation of ortho C–H Bonds in Arylacetamides: C–H Bond Activation Utilizing a Bidentate-Chelation System. ChemCatChem 2012, 4, 1733– 1736, DOI: 10.1002/cctc.201200352
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9a
Ruthenium-Catalyzed Carbonylation of ortho C-H Bonds in Arylacetamides: C-H Bond Activation Utilizing a Bidentate-Chelation System
Shibata, Kaname; Hasegawa, Nao; Fukumoto, Yoshiya; Chatani, Naoto
ChemCatChem (2012), 4 (11), 1733-1736CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
The Ru-catalyzed C-H bond carbonylation of arylacetamides with a 2-pyridinylmethylamine moiety as the bidentate directing group is reported. The reaction involves the regioselective activation of C(sp2)-H bonds at the ortho C-H position. Coordination in an N,N'-fashion is a key step in this reaction. E.g., in presence of Ru3(CO)12 and ethylene in toluene/H2O, carbonylation of amide (I) gave 93% isoquinolinedione deriv. (II).
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(b) Hasegawa, N.; Shibata, K.; Charra, V.; Inoue, S.; Fukumoto, Y.; Chatani, N. Ruthenium-catalyzed cyclocarbonylation of aliphatic amides through the regioselective activation of unactivated C(sp3)–H bonds. Tetrahedron 2013, 69, 4466– 4472, DOI: 10.1016/j.tet.2013.02.006
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9b
Ruthenium-catalyzed cyclocarbonylation of aliphatic amides through the regioselective activation of unactivated C(sp3)-H bonds
Hasegawa, Nao; Shibata, Kaname; Charra, Valentine; Inoue, Satoshi; Fukumoto, Yoshiya; Chatani, Naoto
Tetrahedron (2013), 69 (22), 4466-4472CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)
The regioselective carbonylation of unactivated C(sp3)-H bonds of aliph. amides, using 2-pyridinylmethylamine as a directing group in conjunction with Ru3(CO)12 as a catalyst is described. The presence of a 2-pyridinylmethylamine moiety in the amides is crucial for the success of the reaction. Although ethylene is not incorporated into the products, its presence is also essential for the reaction to proceed. Furthermore, the addn. of H2O is important for the reaction to proceed efficiently. The reaction shows a high preference for the C-H bonds of Me groups, compared to methylene C-H bonds, even the methylene C-H bonds are activated by the presence of an oxygen atom or an aryl group. In addn., the reaction tolerates various functional groups, such as MeO, Cl, CF3, CN, and even Br substituents. The reaction of α-mono-substituted aliph. amides gave the corresponding carbonylation products in lower yields, although the use of α,α-di-substituted aliph. amides resulted in high product yields. The use of a sterically demanding directing group, such as 1-(2-pyridinylethyl)amine moiety, in α-mono-substituted aliph. amides improved the yields of the products. The stoichiometric reaction of an amide with Ru3(CO)12 gave a stable di-nuclear ruthenium complex as a single ruthenium complex in which the 2-pyridinylmethylamino moiety is coordinated to the ruthenium center in a N,N-manner and an amide carbonyl oxygen binds to the other ruthenium center, but C-H bond activation is not involved. The complex itself does not show catalytic activity, but is activated in the presence of H2O under the catalytic reaction conditions employed.
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(c) Misal Castro, L. C.; Obata, A.; Aihara, Y.; Chatani, N. Chelation-Assisted Nickel-Catalyzed Oxidative Annulation via Double C–H Activation/Alkyne Insertion Reaction. Chem. Eur. J. 2016, 22, 1362– 1367, DOI: 10.1002/chem.201504596
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9c
Chelation-Assisted Nickel-Catalyzed Oxidative Annulation via Double C-H Activation/Alkyne Insertion Reaction
Misal Castro, Luis C.; Obata, Atsushi; Aihara, Yoshinori; Chatani, Naoto
Chemistry - A European Journal (2016), 22 (4), 1362-1367CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
A nickel/NHC system for regioselective oxidative annulation by double carbon-hydrogen bond (C-H bond) activation and concomitant alkyne insertion is described. The catalytic reaction requires a bidentate directing group, such as an 8-aminoquinoline, embedded in the substrate. Various 5,6,7,8-tetrasubstituted-N-(8-quinolinyl)-1-naphthamides can be prepd. as well as phenanthrene and benzo[h]quinoline amide derivs. Diarylalkynes, dialkylalkynes, and (aryl)alkynes can be used in the system. A Ni0/NiII catalytic cycle is proposed as the main catalytic cycle. The alkyne plays a double role as a two-component coupling partner and as a hydrogen acceptor. Under optimized conditions the synthesis of the target compds. was achieved using dibromo[1,2-di(methoxy-κO)ethane]nickel [i.e., Ni(dme)Br2, dibromo(glyme)nickel] and 1,3-bis(2,4,6-trimethylphenyl)-1H-imidazolium bromide (i.e., IMes) and 4,5-dihydro-1,3-bis(2,4,6-trimethylphenyl)-1H-imidazolium chloride (i.e., SIMes) as catalyst and ligand combination. Starting materials included alkynes, sych as 1,1'-(1,2-ethynediyl)bis[benzene], 8-hexadecyne, (1-propynyl)benzene, (1-butynyl)ebnzene, (1-hexynyl)benzene, 2-(1-propynyl)thiophene and amides, such as N-(8-quinolinyl)benzamide derivs., 9-methyl-N-(8-quinolinyl)-9H-carbazole-3-carboxamide. The title compds. thus formed included N-(8-quinolinyl)-1-naphthalenecarboxamide derivs.
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(d) He, Z.; Huang, Y. Diverting C–H Annulation Pathways: Nickel-Catalyzed Dehydrogenative Homologation of Aromatic Amides. ACS Catal. 2016, 6, 7814– 7823, DOI: 10.1021/acscatal.6b02477
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9d
Diverting C-H Annulation Pathways: Nickel-Catalyzed Dehydrogenative Homologation of Aromatic Amides
He, Zhiqi; Huang, Yong
ACS Catalysis (2016), 6 (11), 7814-7823CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Direct homologation of arom. amides with internal alkynes has been accomplished via a nickel-catalyzed sequential C-H activation reaction. The use of a rigid chelating group and a strong aprotic polar solvent successfully divert the classical [4+2] annulation to the [2+2+2] homologation pathway. This transformation is promoted by a simple nickel catalyst without the need of stoichiometric metal oxidants. Mechanistic studies support an unusual substrate-assisted ligand exchange process. NMR and X-ray data suggest a [5,5] Ni-bridged metallacycle as the catalyst resting state. Substrate assisted directing group swap plays an important role for the subsequent meta-C-H insertion. In contrast, [4 + 2] annulation can be accomplished using a bulky, electron-rich phosphine ligand, which favors rapid reductive C-N elimination.
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For computational studies of Ni-catalyzed C–H functionalization using N,N-bidentate strategy, see:
(a) Tang, H.; Zhou, B.; Huang, X.-R.; Wang, C.; Yao, J.; Chen, H. Origins of Selective C(sp2)–H Activation Using Transition Metal Complexes with N,N-Bidentate Directing Groups: A Combined Theoretical–Experimental Study. ACS Catal. 2014, 4, 649– 656, DOI: 10.1021/cs401141k
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10a
Origins of Selective C(sp2)-H Activation Using Transition Metal Complexes with N,N-Bidentate Directing Groups: A Combined Theoretical-Experimental Study
Tang, Hao; Zhou, Bingwei; Huang, Xu-Ri; Wang, Congyang; Yao, Jiannian; Chen, Hui
ACS Catalysis (2014), 4 (2), 649-656CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
The strategy using N,N-bidentate directing groups is a promising way to achieve selective C-(sp2)-H activation inaccessible by that of monodentate directing groups. Herein, through theor. calcns., the authors present a rationale behind this strategy, which deciphers its key roles in C-H activation promoted by Ni, Pd, Ru, and Cu. The calcns. reveal two key points: (a) Between the two coordination sites of the N,N-bidentate directing group, the proximal one influences more the C-H activation barrier ΔG‡, whereas the distal site affects more the free energy change ΔG relevant to the substrate coordination. (b) Enlarging/shrinking the chelation ring can exert different effects on the reactivity, depending on the metal identity and the ring size. Importantly, the authors' computational results are in full agreement with previous exptl. findings concerning reactivity. Also, a prediction about the unprecedented reactivity from the authors' theory is confirmed by the authors' expts., lending more credence to the rationale and insights gained.
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(b) Tang, H.; Huang, X.-R.; Yao, J.; Chen, H. Understanding the Effects of Bidentate Directing Groups: A Unified Rationale for sp2 and sp3 C–H Bond Activations. J. Org. Chem. 2015, 80, 4672– 4682, DOI: 10.1021/acs.joc.5b00580
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10b
Understanding the Effects of Bidentate Directing Groups: A Unified Rationale for sp2 and sp3 C-H Bond Activations
Tang, Hao; Huang, Xu-Ri; Yao, Jiannian; Chen, Hui
Journal of Organic Chemistry (2015), 80 (9), 4672-4682CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
Bidentate directing group (DG) strategy is a promising way to achieve sp2 and more inert sp3 C-H bond activations in transition metal (TM) catalysis. In this work, we systematically explored the assisting effects exerted by bidentate DGs in the C-H bond activations. Through DFT calcns. and well-defined comparative anal., we for the first time unified the rationale of the reactivity promoted by bidentate DG in sp2 and sp3 C-H activations, which are generally consistent with available exptl. discoveries about the C-H activation reactivity up to date. In addn. to the general rationale of the reactivity, the assisting effects of several typical bidentate DGs were also quant. evaluated and compared to reveal their relative promoting ability for C-H activation reactivity. Finally, the effect of the ligating group charge and the position of the ligating group charge in bidentate DGs were also investigated, based on which new types of DGs were designed and proposed to be potentially effective in C-H activation. The deeper understanding and new insight about the bidentate DG strategy gained in this work would help to enhance its further exptl. development in sp2 and sp3 C-H bond activations.
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(c) Xu, Z.-Y.; Jiang, Y.-Y.; Yu, H.-Z.; Fu, Y. Mechanism of Nickel(II)-Catalyzed Oxidative C(sp2)–H/C(sp3)–H Coupling of Benzamides and Toluene Derivatives. Chem. - Asian J. 2015, 10, 2479– 2483, DOI: 10.1002/asia.201500599
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10c
Mechanism of Nickel(II)-Catalyzed Oxidative C(sp2)-H/C(sp3)-H Coupling of Benzamides and Toluene Derivatives
Xu, Zheng-Yang; Jiang, Yuan-Ye; Yu, Hai-Zhu; Fu, Yao
Chemistry - An Asian Journal (2015), 10 (11), 2479-2483CODEN: CAAJBI; ISSN:1861-4728. (Wiley-VCH Verlag GmbH & Co. KGaA)
The Ni-catalyzed C(sp2)-H/C(sp3)-H coupling of benzamides with toluene derivs. was recently successfully achieved with mild oxidant iC3F7I. Herein, we employ d. functional theory (DFT) methods to resolve the mechanistic controversies. Two previously proposed mechanisms are excluded, and our proposed mechanism involving iodine-atom transfer (IAT) between iC3F7I and the NiII intermediate was found to be more feasible. With this mechanism, the presence of a carbon radical is consistent with the exptl. observation that (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) completely quenches the reaction. Meanwhile, the hydrogen-atom abstraction of toluene is irreversible and the activation of the C(sp2)-H bond of benzamides is reversible. Both of these conclusions are in good agreement with Chatanis deuterium-labeling expts.
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(d) Singh, S.; K, S.; Sunoj, R. B. Aliphatic C(sp3)–H Bond Activation Using Nickel Catalysis: Mechanistic Insights on Regioselective Arylation. J. Org. Chem. 2017, 82, 9619– 9626, DOI: 10.1021/acs.joc.7b01672
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10d
Aliphatic C(sp3)-H Bond Activation Using Nickel Catalysis: Mechanistic Insights on Regioselective Arylation
Singh, Sukriti; K, Surya; Sunoj, Raghavan B.
Journal of Organic Chemistry (2017), 82 (18), 9619-9626CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
Transition-metal-catalyzed C(sp3)-H bond activation in aliph. compds. are of current interest. Lack of mechanistic insights on Ni-catalyzed C(sp3)-H activation using 8-aminoquinoline as a directing group motivated us to examine an interesting direct arylation of an aliph. tertiary amide by using d. functional theory. The catalysis employed Ni(II) precatalyst, 4-iodoanisole as an arylating agent, sodium carbonate, and mesitylenic acid as additives in DMF solvent. Examn. of a comprehensive set of mechanistic pathways helped us learn that the most preferred route begins with a bidentate chelate binding of deprotonated substrate to the Ni. The C-H activation in the catalyst-substrate complex via a cyclometalation deprotonation provides a five-membered nickelacycle intermediate, which upon the rate-limiting oxidative insertion to aryl iodide forms a Ni(IV)-aryl intermediate. The ensuing reductive elimination furnishes the desired arylated product. We note that the explicit inclusion of sodium carbonate, mesitylenic acid, and solvent mols. on sodium ion all are crit. in identifying the most favorable pathway. Of the two types of C(sp3)-H bonds in the substrate [2-methyl-2-phenyl-N-(quinolin-8-yl)heptanamide], the energies for the regio-controlling reductive elimination is predicted to be more in favor of the Me group than the methylene of the pentyl chain, in excellent agreement with the previous exptl. observation.
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(e) Omer, H. M.; Liu, P. Computational Study of Ni-Catalyzed C–H Functionalization: Factors That Control the Competition of Oxidative Addition and Radical Pathways. J. Am. Chem. Soc. 2017, 139, 9909– 9920, DOI: 10.1021/jacs.7b03548
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10e
Computational Study of Ni-Catalyzed C-H Functionalization: Factors That Control the Competition of Oxidative Addition and Radical Pathways
Omer, Humair M.; Liu, Peng
Journal of the American Chemical Society (2017), 139 (29), 9909-9920CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The mechanisms of Ni-catalyzed C-H arylation, alkylation, and sulfenylation with N,N-bidentate directing groups are investigated using d. functional theory (DFT) calcns. While the C-H cleavage occurs via the concerted metalation-deprotonation (CMD) mechanism in all types of reactions, the subsequent C-C and C-X bond formation steps may occur via either oxidative addn. to form a Ni(IV) intermediate or radical pathways involving Ni(III) complexes generated from homolytic dissocn. of disulfides/peroxides or halide-atom transfer from alkyl halides. DFT calcns. revealed that radical mechanisms are preferred in reactions with sterically hindered coupling partners with relatively low bond dissocn. energies (BDE) such as dicumyl peroxide, heptafluoroisopropyl iodide and di-Ph disulfide. In contrast, these radical processes are highly disfavored when generating unstable Ph and primary alkyl radicals. In such cases, the reaction proceeds via an oxidative addn./reductive elimination mechanism involving a Ni(IV) intermediate. These theor. insights into the substrate-controlled mechanisms in the C-H functionalizations were employed to investigate a no. of exptl. phenomena including substituent effects on reactivity, chemo- and regioselectivity and the effects of oxidant in the intermol. oxidative C-H/C-H coupling reactions.
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(f) Haines, B. E.; Yu, J.-Q.; Musaev, D. G. The mechanism of directed Ni(II)-catalyzed C–H iodination with molecular iodine. Chem. Sci. 2018, 9, 1144– 1154, DOI: 10.1039/C7SC04604A
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10f
The mechanism of directed Ni(II)-catalyzed C-H iodination with molecular iodine
Haines, Brandon E.; Yu, Jin-Quan; Musaev, Djamaladdin G.
Chemical Science (2018), 9 (5), 1144-1154CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
The d. functional theory method is used to elucidate the elementary steps of Ni(II)-catalyzed C(sp2)-H iodination with I2 and substrates bearing N,N'-bidentate directing centers, amide-oxazoline (AO) and 8-aminoquinoline (AQ). The relative stability of the lowest energy high- and low-spin electronic states of the catalyst and intermediates is found to be an important factor for all of the steps in the reaction. As a result, two-state reactivity for these systems is reported, where the reaction is initiated on the triplet surface and generates a high energy singlet nickelacycle. It is shown that the addn. of Na2CO3 base to the reaction mixt. facilitates C-H activation. The presence of I2 in the reaction provides the much needed driving force for the C-H activation and nickelacycle formation and ultimately reacts to form a new C-I bond through either a redox neutral electrophilic cleavage (EC) pathway or a one-electron reductive cleavage (REC) pathway. The previously proposed Ni(II)/Ni(IV) and homolytic cleavage pathways are found to be higher in energy. The nature of the substrate is found to have a large impact on the relative stability of the lowest electronic states and on the stability of the nickelacycle resulting from C-H activation.
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(g) Li, Y.; Zou, L.; Bai, R.; Lan, Y. Ni(I)–Ni(III) vs. Ni(II)–Ni(IV): mechanistic study of Ni-catalyzed alkylation of benzamides with alkyl halides. Org. Chem. Front. 2018, 5, 615– 622, DOI: 10.1039/C7QO00850C
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10g
Ni(I)-Ni(III) vs. Ni(II)-Ni(IV): mechanistic study of Ni-catalyzed alkylation of benzamides with alkyl halides
Li, Yingzi; Zou, Lufeng; Bai, Ruopeng; Lan, Yu
Organic Chemistry Frontiers (2018), 5 (4), 615-622CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
Nickel-catalyzed C-H bond activation has attracted significant attention for the construction of C-C bond frameworks. We report d. functional theory investigations into the mechanism of nickel-catalyzed alkylation of benzamides with alkyl halides. Both the Ni(I)-Ni(III) and Ni(II)-Ni(IV) catalytic cycles were considered. The theor. study indicated that the most feasible mechanism involved a Ni(II)-Ni(IV) catalytic cycle with four main steps: (i) N-H bond activation and (ii) C-H bond activation through the concerted metalation-deprotonation pathway, (iii) oxidative addn. of BuBr to give a high-valent Ni(IV) complex, and (iv) C-C reductive elimination to generate the product and the active catalyst. The rate-detg. step of the favored pathway is the oxidative addn., leading to the generation of a Ni(IV) intermediate. In addn., the present study casts light on the role of PPh3, which accelerates the cleavage of N-H bond. Frontier MO theory and natural population anal. were employed to explain the effect of the phosphine ligand on the structure of the Ni complex.
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11
For computational studies of other metal-catalyzed C–H functionalization using N,N-bidentate group strategy, see:
(a) Cross, W. B.; Hope, E. G.; Lin, Y.-H.; Macgregor, S. A.; Singh, K.; Solan, G. A.; Yahyaa, N. N,N-Chelate-control on the regioselectivity in acetate-assisted C–H activation. Chem. Commun. 2013, 49, 1918– 1920, DOI: 10.1039/c3cc38697j
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11a
N,N-Chelate-control on the regioselectivity in acetate-assisted C-H activation
Cross, Warren B.; Hope, Eric G.; Lin, Yi-Hsien; Macgregor, Stuart A.; Singh, Kuldip; Solan, Gregory A.; Yahya, Nurhusna
Chemical Communications (Cambridge, United Kingdom) (2013), 49 (19), 1918-1920CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Preferential peri- vs. more common ortho-cyclopalladation was achieved in reaction of 1-[6-(iminoethyl)-2-pyridyl]naphthalene with palladium acetate, producing tridentate C,N,N-ligated pincer complex; 6-aminoethyl- analog also metalates in peri-position, whereas 6-hydroxyethyl undergoes ortho-palladation with formation of C2,N,O-pincer. Bidentate N,N-pyridylimine or N,N-pyridylamine donors are effective chelating ligands for regiospecific C-H activation at the peri-(C8)-position of a naphthyl ring on reaction with palladium(ii) acetate; DFT calcns. show N,N-chelates bias the cyclopalladation towards 6-membered ring products.
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(b) Huang, L.; Li, Q.; Wang, C.; Qi, C. Palladium(II)-Catalyzed Regioselective Arylation of Naphthylamides with Aryl Iodides Utilizing a Quinolinamide Bidentate System. J. Org. Chem. 2013, 78, 3030– 3038, DOI: 10.1021/jo400017v
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11b
Palladium(II)-Catalyzed Regioselective Arylation of Naphthylamides with Aryl Iodides Utilizing a Quinolinamide Bidentate System
Huang, Lehao; Li, Qian; Wang, Chen; Qi, Chenze
Journal of Organic Chemistry (2013), 78 (7), 3030-3038CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
A palladium(II)-catalyzed quinolinamide-directed 8-arylation of 1-naphthylamides with aryl iodides is reported. The bidentate directing group (quinolinamide) proved to be crucial for a highly regioselective transformation. E.g., in presence of Pd(OAc)2 and KOAc in xylene, arylation of N-(1-naphthyl)quinoline-2-carboxamide (I) with 4-iodotoluene gave 85% II. In addn., the amide directing group can be easily hydrolyzed under basic conditions to offer a range of 8-aryl-1-naphthylamine derivs. The theor. calcns. suggest that the C-H arylation reaction proceeds through a sequential C-H activation/oxidative addn. pathway.
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(c) Wei, Y.; Tang, H.; Cong, X.; Rao, B.; Wu, C.; Zeng, X. Pd(II)-Catalyzed Intermolecular Arylation of Unactivated C(sp3)–H Bonds with Aryl Bromides Enabled by 8-Aminoquinoline Auxiliary. Org. Lett. 2014, 16, 2248– 2251, DOI: 10.1021/ol500745t
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11c
Pd(II)-Catalyzed Intermolecular Arylation of Unactivated C(sp3)-H Bonds with Aryl Bromides Enabled by 8-Aminoquinoline Auxiliary
Wei, Yu; Tang, Huarong; Cong, Xuefeng; Rao, Bin; Wu, Chao; Zeng, Xiaoming
Organic Letters (2014), 16 (8), 2248-2251CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
An example of using readily available, less reactive aryl bromides as arylating reagents in the Pd(II)-catalyzed intermol. arylation of unactivated C(sp3)-H bonds is described. This reaction was promoted by a crucial 8-aminoquinolinyl directing group and a K2CO3 base, enabling regiospecific installation of an aryl scaffold at the β-position of carboxamides. A mechanistic study by DFT calcns. reveals a C(sp3)-H activation-led pathway featuring the oxidative addn. as the highest energy transition state.
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(d) Shan, C.; Luo, X.; Qi, X.; Liu, S.; Li, Y.; Lan, Y. Mechanism of Ruthenium-Catalyzed Direct Arylation of C–H Bonds in Aromatic Amides: A Computational Study. Organometallics 2016, 35, 1440– 1445, DOI: 10.1021/acs.organomet.6b00064
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11d
Mechanism of Ruthenium-Catalyzed Direct Arylation of C-H Bonds in Aromatic Amides: A Computational Study
Shan, Chunhui; Luo, Xiaoling; Qi, Xiaotian; Liu, Song; Li, Yingzi; Lan, Yu
Organometallics (2016), 35 (10), 1440-1445CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Ruthenium-catalyzed arylation of ortho C-H bonds directed by a bidentate 8-aminoquinoline moiety not only is important to construct new biaryl derivates but also merges important research areas. In this study, the d. functional theory (DFT) method M11-L was employed to predict the mechanism of this C-H bond arylation reaction. The computational results indicate that the initial step for this reaction is catalyst loading by electrophilic deprotonation to generate a substrate-coordinated Ru(II) intermediate, which is the key compd. in the complete catalytic cycle. The catalytic cycle includes electrophilic deprotonation by carbonate, oxidative addn. of bromobenzene, reductive elimination to form a new aryl-aryl bond, proton transfer to release the product, and ligand exchange to regenerate the initial Ru(II) intermediate. Theor. calcns. suggest that the oxidative addn. of bromobenzene is the rate-detg. step of the whole catalytic cycle, and the apparent activation free energy is 32.7 kcal/mol. The ligand effect was considered in DFT calcns., and the calcd. results agree well with exptl. observations.
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(e) Chen, C.; Hao, Y.; Zhang, T.-Y.; Pan, J.-L.; Ding, J.; Xiang, H.-Y.; Wang, M.; Ding, T.-M.; Duan, A.; Zhang, S.-Y. Computational and experimental studies on copper-mediated selective cascade C–H/N–H annulation of electron-deficient acrylamide with arynes. Chem. Commun. 2019, 55, 755– 758, DOI: 10.1039/C8CC08708C
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11e
Computational and experimental studies on copper-mediated selective cascade C-H/N-H annulation of electron-deficient acrylamide with arynes
Chen, Chao; Hao, Yu; Zhang, Ting-Yu; Pan, Jin-Long; Ding, Jun; Xiang, Heng-Ye; Wang, Man; Ding, Tong-Mei; Duan, Abing; Zhang, Shu-Yu
Chemical Communications (Cambridge, United Kingdom) (2019), 55 (6), 755-758CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
An efficient and convenient copper-mediated method has been developed to achieve direct cascade C-H/N-H annulation for the synthesis of 2-quinolinones e.g., I from electron-deficient acrylamides e.g., II and arynes e.g., 4,5-dimethyl-2-(trimethylsilyl)phenyl trifluoromethanesulfonate. This method highlights an emerging but simple strategy to transform inert C-H bonds into versatile functional groups in org. synthesis to provide a new method of synthesizing 2-quinolinones efficiently. Mechanistic investigation by exptl. and d. functional theory (DFT) studies suggest that an organometallic C-H activation via a Cu(III) intermediate is likely to be involved in the reaction.
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(f) Dewyer, A. L.; Zimmerman, P. M. Simulated Mechanism for Palladium Catalyzed, Directed γ-Arylation of Piperidine. ACS Catal. 2017, 7, 5466– 5477, DOI: 10.1021/acscatal.7b01390
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11f
Simulated Mechanism for Palladium-Catalyzed, Directed γ-Arylation of Piperidine
Dewyer, Amanda L.; Zimmerman, Paul M.
ACS Catalysis (2017), 7 (8), 5466-5477CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Quantum chem. reaction path finding methods are herein used to investigate the mechanism of Pd-catalyzed distal functionalization of piperidine, as reported by Sanford. These methods allowed navigation of a complex reaction landscape with multiple reactants interacting at all key steps of the proposed catalytic cycle. A multistep cycle is shown to conceptually begin with substrate ligation and Pd(II)-catalyzed C-H activation, which occurs through concerted metalation-deprotonation. In subsequent steps, the kinetic and thermodn. profiles for oxidative addn., reductive elimination, and catalyst regeneration show why excess Cs salts and ArI were required in the expt. Specifically, excess ArI is necessary to thermodynamically overcome the high energy of the C-H activated intermediate and allow oxidative addn. to be favorable, and excess Cs salt is needed to sequester reaction byproducts during oxidative addn. and catalyst regeneration. The overall catalytic profile is consistent with rate-limiting C-H activation, explains the probable functions of all major exptl. conditions, and gives atomistic detail to guide expt. to improve this challenging transformation even further.
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Shiota, H.; Ano, Y.; Aihara, Y.; Fukumoto, Y.; Chatani, N. Nickel-Catalyzed Chelation-Assisted Transformations Involving Ortho C–H Bond Activation: Regioselective Oxidative Cycloaddition of Aromatic Amides to Alkynes. J. Am. Chem. Soc. 2011, 133, 14952– 14955, DOI: 10.1021/ja206850s
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12
Nickel-catalyzed chelation-assisted transformations involving ortho C-H bond activation: regioselective oxidative cycloaddition of aromatic amides to alkynes
Shiota, Hirotaka; Ano, Yusuke; Aihara, Yoshinori; Fukumoto, Yoshiya; Chatani, Naoto
Journal of the American Chemical Society (2011), 133 (38), 14952-14955CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Although the pioneering example of ortho metalation involving cleavage of C-H bonds was achieved using a nickel complex, no examples of catalysis using nickel complexes have been reported. In this work, the Ni-catalyzed transformation of ortho C-H bonds utilizing chelation assistance, such as oxidative cycloaddn. of arom. amides with alkynes, has been achieved.
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For a recent computational study on this reaction, see:Zhang, X.; Zhao, Q.; Fan, J.-Q.; Chen, D.-Z.; Liu, J.-B. A computational mechanistic study of Ni(0)-catalyzed annulation of aromatic amides with alkynes: the effects of directing groups. Org. Chem. Front. 2019, DOI: 10.1039/C8QO01310A
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There is no corresponding record for this reference.
14
For select examples of chelation-assisted Ni-catalyzed C–H arylation, see:
(a) Aihara, Y.; Chatani, N. Nickel-Catalyzed Direct Arylation of C(sp3)–H Bonds in Aliphatic Amides via Bidentate-Chelation Assistance. J. Am. Chem. Soc. 2014, 136, 898– 901, DOI: 10.1021/ja411715v
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14a
Nickel-Catalyzed Direct Arylation of C(sp3)-H Bonds in Aliphatic Amides via Bidentate-Chelation Assistance
Aihara, Yoshinori; Chatani, Naoto
Journal of the American Chemical Society (2014), 136 (3), 898-901CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The Ni-catalyzed, direct arylation of C-(sp3)-H (Me and methylene) bonds in aliph. amides contg. an 8-aminoquinoline moiety as a bidentate directing group with aryl halides is described. Deuterium-labeling expts. indicate that the C-H bond cleavage step is fast and reversible. Various nickel complexes including both Ni-(II) and Ni(0) show a high catalytic activity. The results of a series of mechanistic expts. indicate that the catalytic reaction does not proceed through a Ni(0)/Ni-(II) catalytic cycle, but probably through a Ni-(II)/Ni-(IV) catalytic cycle.
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(b) Yokota, A.; Aihara, Y.; Chatani, N. Nickel(II)-Catalyzed Direct Arylation of C–H Bonds in Aromatic Amides Containing an 8-Aminoquinoline Moiety as a Directing Group. J. Org. Chem. 2014, 79, 11922– 11932, DOI: 10.1021/jo501697n
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14b
Nickel(II)-Catalyzed Direct Arylation of C-H Bonds in Aromatic Amides Containing an 8-Aminoquinoline Moiety as a Directing Group
Yokota, Ayana; Aihara, Yoshinori; Chatani, Naoto
Journal of Organic Chemistry (2014), 79 (24), 11922-11932CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
Arylation via the cleavage of the ortho C-H bonds by a nickel-catalyzed reaction of arom. amides contg. an 8-aminoquinoline moiety with aryl iodides is reported. The reaction shows a high functional group compatibility. The reaction proceeds in a highly selective manner at the less hindered C-H bonds in the reaction of meta-substituted arom. amides, irresp. of the electronic nature of the substituents. Electron-withdrawing groups on the arom. amides facilitate the reaction. Various mechanistic expts., such as deuterium labeling expts., Hammett studies, competition expts., and radical trap expts., were made for better understanding the reaction mechanism. The cleavage of C-H bonds is reversible from the deuterium labeling expts. Both Ni(II) and Ni(0) show a high catalytic activity, but the results of mechanistic expts. suggest that a Ni(0)/Ni(II) catalytic cycle is not involved.
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(c) Li, M.; Dong, J.; Huang, X.; Li, K.; Wu, Q.; Song, F.; You, J. Nickel-catalyzed chelation-assisted direct arylation of unactivated C(sp3)–H bonds with aryl halides. Chem. Commun. 2014, 50, 3944– 3946, DOI: 10.1039/C4CC00716F
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14c
Nickel-catalyzed chelation-assisted direct arylation of unactivated C(sp3)-H bonds with aryl halides
Li, Mingliang; Dong, Jiaxing; Huang, Xiaolei; Li, Kaizhi; Wu, Qian; Song, Feijie; You, Jingsong
Chemical Communications (Cambridge, United Kingdom) (2014), 50 (30), 3944-3946CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
In this work, we have disclosed the nickel-catalyzed unactivated β-C(sp3)-H bond arylation of aliph. acid derivs. with aryl iodides/bromides via bidentate chelation-assistance of an 8-aminoquinoline moiety. E.g., in presence of a Ni catalyst, arylation of 8-quinolinyl-substituted amide I with 4-IC6H4OMe gave 83% II. The best results were obtained by using Ni(OTf)2 as the catalyst, PPh3 as the ligand, Na2CO3 as the base, PivOH, and DMSO as the additives in dry 1,4-dioxane at 160 °C. These preliminary results indicate the intrinsic catalytic potential of nickel metal for unactivated C(sp3)-H bond arylation.
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For select examples of chelation-assisted Ni-catalyzed C–H alkylation, see:
(a) Kubo, T.; Chatani, N. Dicumyl Peroxide as a Methylating Reagent in the Ni-Catalyzed Methylation of Ortho C–H Bonds in Aromatic Amides. Org. Lett. 2016, 18, 1698– 1701, DOI: 10.1021/acs.orglett.6b00658
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15a
Dicumyl Peroxide as a Methylating Reagent in the Ni-Catalyzed Methylation of Ortho C-H Bonds in Aromatic Amides
Kubo, Teruhiko; Chatani, Naoto
Organic Letters (2016), 18 (7), 1698-1701CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
The direct methylation of ortho C-H bonds in arom. amides, e.g., I (R = OMe, Me, Ph, CN, etc.), with dicumyl peroxide (DCP) using a nickel complex as the catalyst is reported. The reaction shows a high functional group tolerance and is inhibited by radical scavengers. In reactions of meta-substituted arom. amides, the reaction proceeds in a highly selective manner at the less hindered C-H bonds.
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(b) Aihara, Y.; Chatani, N. Nickel-Catalyzed Direct Alkylation of C–H Bonds in Benzamides and Acrylamides with Functionalized Alkyl Halides via Bidentate-Chelation Assistance. J. Am. Chem. Soc. 2013, 135, 5308– 5311, DOI: 10.1021/ja401344e
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15b
Nickel-Catalyzed Direct Alkylation of C-H Bonds in Benzamides and Acrylamides with Functionalized Alkyl Halides via Bidentate-Chelation Assistance
Aihara, Yoshinori; Chatani, Naoto
Journal of the American Chemical Society (2013), 135 (14), 5308-5311CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The alkylation of the ortho C-H bonds in benzamides and acrylamides contg. an 8-aminoquinoline moiety as a bidentate directing group with unactivated alkyl halides using nickel complexes as catalysts is described. E.g., in presence of Ni(OTf)2 and PPh3 in toluene, butylation of 8-aminoquinoline deriv. (I) by BuBr gave 81% II. The reaction shows high functional group compatibility. In reactions of meta-substituted arom. amides, the reaction proceeds in a highly selective manner at the less hindered C-H bond.
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(c) Wu, X.; Zhao, Y.; Ge, H. Nickel-Catalyzed Site-Selective Alkylation of Unactivated C(sp3)–H Bonds. J. Am. Chem. Soc. 2014, 136, 1789– 1792, DOI: 10.1021/ja413131m
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15c
Nickel-Catalyzed Site-Selective Alkylation of Unactivated C(sp3)-H Bonds
Wu, Xuesong; Zhao, Yan; Ge, Haibo
Journal of the American Chemical Society (2014), 136 (5), 1789-1792CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The direct alkylation of unactivated sp3 C-H bonds of aliph. amides was achieved via nickel catalysis with the assist of a bidentate directing group. The reaction favors the C-H bonds of Me groups over the methylene C-H bonds and tolerates various functional groups. E.g., in presence of Ni(acac)2, 1,2-bis(diphenylphosphino)benzene, and Cs2CO3 in toluene, alkylation of 2-ethyl-2-methyl-N-(quinolin-8-yl)pentanamide with 1-iodopentane gave 89% I. Moreover, this reaction shows a predominant preference for sp3 C-H bonds of Me groups via a five-membered ring intermediate over the sp2 C-H bonds of arenes in the cyclometalation step.
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(d) Song, W.; Lackner, S.; Ackermann, L. Nickel-Catalyzed C–H Alkylations: Direct Secondary Alkylations and Trifluoroethylations of Arenes. Angew. Chem., Int. Ed. 2014, 53, 2477– 2480, DOI: 10.1002/anie.201309584
[ Crossref], [ PubMed], [ CAS], Google Scholar
15d
Nickel-Catalyzed C-H Alkylations: Direct Secondary Alkylations and Trifluoroethylations of Arenes
Song, Weifeng; Lackner, Sebastian; Ackermann, Lutz
Angewandte Chemie, International Edition (2014), 53 (9), 2477-2480CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A versatile nickel catalyst allowed for C-H alkylations of unactivated arenes with challenging secondary alkyl bromides and chlorides. The high catalytic efficacy also set the stage for direct secondary alkylations of indoles as well as C-H trifluoroethylations with ample substrate scope.
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For select examples of chelation-assisted Ni-catalyzed C–H benzylation, see:
(a) Aihara, Y.; Tobisu, M.; Fukumoto, Y.; Chatani, N. Ni(II)-Catalyzed Oxidative Coupling between C(sp2)–H in Benzamides and C(sp3)–H in Toluene Derivatives. J. Am. Chem. Soc. 2014, 136, 15509– 15512, DOI: 10.1021/ja5095342
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16a
Ni(II)-Catalyzed Oxidative Coupling between C(sp2)-H in Benzamides and C(sp3)-H in Toluene Derivatives
Aihara, Yoshinori; Tobisu, Mamoru; Fukumoto, Yoshiya; Chatani, Naoto
Journal of the American Chemical Society (2014), 136 (44), 15509-15512CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Oxidative coupling between C(sp2)-H bonds and C(sp3)-H bonds is achieved by the Ni(II)-catalyzed reaction of benzamides contg. an 8-aminoquinoline moiety as the directing group with toluene derivs. in the presence of heptafluoroisopropyl iodide as the oxidant. The method has a broad scope and shows high functional group compatibility e. g., I. Toluene derivs. can be used as the coupling partner in an unreactive solvent.
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(b) Soni, V.; Khake, S. M.; Punji, B. Nickel-Catalyzed C(sp2)–H/C(sp3)–H Oxidative Coupling of Indoles with Toluene Derivatives. ACS Catal. 2017, 7, 4202– 4208, DOI: 10.1021/acscatal.7b01044
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16b
Nickel-Catalyzed C(sp2)-H/C(sp3)-H Oxidative Coupling of Indoles with Toluene Derivatives
Soni, Vineeta; Khake, Shrikant M.; Punji, Benudhar
ACS Catalysis (2017), 7 (6), 4202-4208CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Nickel-catalyzed oxidative C(sp2)-H/C(sp3)-H coupling of indoles with toluene derivs. is successfully achieved in the presence of 2-iodobutane as the oxidant. This method allows the selective C-2 benzylation of indoles with toluene derivs. over the alkylation with 2-iodobutane and permits the coupling of diversified indoles via the monochelation assistance. The reaction proceeded through a single-electron-transfer (SET) process, wherein both the C-H nickelation of indole and the C-H activation of toluene derivs. have a significant effect on the entire reaction rate. The synthetic utility of this nickel-catalyzed protocol is demonstrated by the facile removal of the directing group and by the convenient synthesis of the melatonin receptor antagonist Luzindole derivs.
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For select examples of chelation-assisted Ni-catalyzed C–H thiolation, see:
(a) Yan, S.-Y.; Liu, Y.-J.; Liu, B.; Liu, Y.-H.; Shi, B.-F. Nickel-catalyzed thiolation of unactivated aryl C–H bonds: efficient access to diverse aryl sulfides. Chem. Commun. 2015, 51, 4069– 4072, DOI: 10.1039/C4CC10446C
[ Crossref], [ PubMed], [ CAS], Google Scholar
17a
Nickel-catalyzed thiolation of unactivated aryl C-H bonds: efficient access to diverse aryl sulfides
Yan, Sheng-Yi; Liu, Yue-Jin; Liu, Bin; Liu, Yan-Hua; Shi, Bing-Feng
Chemical Communications (Cambridge, United Kingdom) (2015), 51 (19), 4069-4072CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
A nickel-catalyzed thiolation of unactivated C(sp2)-H bonds with disulfides employing the PIP directing group was described. This process uses a catalytic nickel catalyst and no metallic oxidants or cocatalysts are required. The reaction tolerates various important functional groups and heteroarenes, providing an efficient synthetic pathway to access diverse diaryl sulfides.
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(b) Yan, S.-Y.; Liu, Y.-J.; Liu, B.; Liu, Y.-H.; Zhang, Z.-Z.; Shi, B.-F. Nickel-catalyzed direct thiolation of unactivated C(sp3)–H bonds with disulfides. Chem. Commun. 2015, 51, 7341– 7344, DOI: 10.1039/C5CC01436K
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17b
Nickel-catalyzed direct thiolation of unactivated C(sp3)-H bonds with disulfides
Yan, Sheng-Yi; Liu, Yue-Jin; Liu, Bin; Liu, Yan-Hua; Zhang, Zhuo-Zhuo; Shi, Bing-Feng
Chemical Communications (Cambridge, United Kingdom) (2015), 51 (34), 7341-7344CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
The first nickel-catalyzed thiolation of unactivated C(sp3)-H bonds with disulfides was described. This transformation uses (dppp)NiCl2 as a catalyst and BINOL as a ligand, which are efficient for the thiolation of β-Me C(sp3)-H bonds of a broad range of aliph. carboxamides. The reaction provides an efficient synthetic pathway to access diverse thioethers.
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(c) Lin, C.; Li, D.; Wang, B.; Yao, J.; Zhang, Y. Direct ortho-Thiolation of Arenes and Alkenes by Nickel Catalysis. Org. Lett. 2015, 17, 1328– 1331, DOI: 10.1021/acs.orglett.5b00337
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17c
Direct ortho-Thiolation of Arenes and Alkenes by Nickel Catalysis
Lin, Cong; Li, Danyang; Wang, Binjie; Yao, Jinzhong; Zhang, Yuhong
Organic Letters (2015), 17 (5), 1328-1331CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
The direct thiolation of 8-quinonlinyl-substituted arenes and alkenes with diaryl disulfides was developed with nickel catalysis. The reaction displayed exceptional compatibility with a wide range of functional groups to regioselectively give the diaryl sulfides and alkenyl sulfides in high yields. E.g., in presence of NiCl2, Na2CO3, TBAI and o-nitrobenzoic acid in DMSO under N2, thiolation of 8-quinonlinyl-substituted arene I with 4-MeOC6H4SSC6H4OMe-4 gave 92% thioether II.
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(d) Reddy, V. P.; Qiu, R.; Iwasaki, T.; Kambe, N. Nickel-catalyzed synthesis of diaryl sulfides and sulfones via C–H bond functionalization of arylamides. Org. Biomol. Chem. 2015, 13, 6803– 6813, DOI: 10.1039/C5OB00149H
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17d
Nickel-catalyzed synthesis of diarylsulfides and sulfones via C-H bond functionalization of arylamides
Reddy, Vutukuri Prakash; Qiu, Renhua; Iwasaki, Takanori; Kambe, Nobuaki
Organic & Biomolecular Chemistry (2015), 13 (24), 6803-6813CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
The direct sulfenylation and sulfonylation of (sp2)C-H bonds of benzamide derivs. were achieved using a Ni catalyst with the aid of an 8-aminoquinoline moiety as a bidentate directing group. These protocols represent a convenient route for the formation of valuable diaryl sulfides and sulfones in moderate to excellent yields.
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Aihara, Y.; Chatani, N. Nickel-Catalyzed Reaction of C–H Bonds in Amides with I2: ortho-Iodination via the Cleavage of C(sp2)–H Bonds and Oxidative Cyclization to β-Lactams via the Cleavage of C(sp3)–H Bonds. ACS Catal. 2016, 6, 4323– 4329, DOI: 10.1021/acscatal.6b00964
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18
Nickel-Catalyzed Reaction of C-H Bonds in Amides with I2: ortho-Iodination via the Cleavage of C(sp2)-H Bonds and Oxidative Cyclization to β-Lactams via the Cleavage of C(sp3)-H Bonds
Aihara, Yoshinori; Chatani, Naoto
ACS Catalysis (2016), 6 (7), 4323-4329CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
The first example of the nickel(II)-catalyzed reaction of amides using inexpensive and milder mol. iodine (I2) as an iodinating reagent is reported. The reaction of arom. amides having an 8-amino-5-choloroquinoline as a directing group with I2 resulted in the prodn. of ortho-iodination products. Deuterium labeling expts. indicate that the cleavage of C-H bonds is irreversible and is likely the rate-detg. step, which is in sharp contrast to the previously reported transformation using the same Ni(II) catalyst/8-aminoquinoline chelation system. The reaction is applicable to the synthesis of β-lactams from aliph. amides as the substrate, in which C(sp3)-H bonds are activated. The results of deuterium labeling expts. indicate that the cleavage of C(sp3)-H bonds is also irreversible.
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Nakao, Y.; Morita, E.; Idei, H.; Hiyama, T. Dehydrogenative [4 + 2] Cycloaddition of Formamides with Alkynes through Double C–H Activation. J. Am. Chem. Soc. 2011, 133, 3264– 3267, DOI: 10.1021/ja1102037
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19
Dehydrogenative [4 + 2] Cycloaddition of Formamides with Alkynes through Double C-H Activation
Nakao, Yoshiaki; Morita, Eiji; Idei, Hiroaki; Hiyama, Tamejiro
Journal of the American Chemical Society (2011), 133 (10), 3264-3267CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Formamides having 1-arylalkyl groups, e.g., I, on nitrogen undergo an unprecedented dehydrogenative [4 + 2] cycloaddn. reaction with alkynes via nickel/AlMe3 cooperative catalysis to give highly substituted dihydropyridone derivs., e.g., II, in good yields. Notably, the transformation proceeds through double functionalization of C(sp2)-H and C(sp3)-H bonds in the formamides.
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(a) Lin, C.; Chen, Z.; Liu, Z.; Zhang, Y. Nickel-Catalyzed Stereoselective Alkenylation of C(sp3)–H Bonds with Terminal Alkynes. Org. Lett. 2017, 19, 850– 853, DOI: 10.1021/acs.orglett.6b03856
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20a
Nickel-Catalyzed Stereoselective Alkenylation of C(sp3)-H Bonds with Terminal Alkynes
Lin, Cong; Chen, Zhengkai; Liu, Zhanxiang; Zhang, Yuhong
Organic Letters (2017), 19 (4), 850-853CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
A nickel-catalyzed stereoselective alkenylation of an unactivated β-C(sp3)-H bonds in aliph. amides with terminal alkynes using 8-aminoquinoline auxiliary is reported for the first time. This reaction displays excellent functional group tolerance with respect to both aliph. amides and terminal alkynes and features a cheap nickel catalytic system. The 8-aminoquinolyl directing group could be smoothly removed, and the resultant β-styrylcarboxylic acid derivs. could serve as versatile building blocks for further transformation.
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(b) Li, M.; Yang, Y.; Zhou, D.; Wan, D.; You, J. Nickel-Catalyzed Addition-Type Alkenylation of Unactivated, Aliphatic C–H Bonds with Alkynes: A Concise Route to Polysubstituted γ-Butyrolactones. Org. Lett. 2015, 17, 2546– 2549, DOI: 10.1021/acs.orglett.5b01128
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20b
Nickel-Catalyzed Addition-Type Alkenylation of Unactivated, Aliphatic C-H Bonds with Alkynes: A Concise Route to Polysubstituted γ-Butyrolactones
Li, Mingliang; Yang, Yudong; Zhou, Danni; Wan, Danyang; You, Jingsong
Organic Letters (2015), 17 (10), 2546-2549CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
Through the nickel-catalyzed chelation-assisted C-H bond activation strategy, the addn.-type alkenylation of unreactive β-C(sp3)-H bonds of aliph. amides with internal alkynes is developed for the first time to produce γ,δ-unsatd. carboxylic amide derivs. [e.g., amide I + PhC≡CPh → γ,δ-unsatd. amide II (78% optimized, E/Z 1/2.8) using Ni(OAc)2 and PPh3 in i-PrOH/toluene]. The resulting alkenylated products can further be transformed into polysubstituted γ-butyrolactones with pyridinium chlorochromate (PCC) [e.g., III → IV (78%)].
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(c) Maity, S.; Agasti, S.; Earsad, A. M.; Hazra, A.; Maiti, D. Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient Olefins into Unactivated sp3 C–H Bonds. Chem. - Eur. J. 2015, 21, 11320– 11324, DOI: 10.1002/chem.201501962
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20c
Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient Olefins into Unactivated sp3 C-H Bonds
Maity, Soham; Agasti, Soumitra; Earsad, Arif Mahammad; Hazra, Avijit; Maiti, Debabrata
Chemistry - A European Journal (2015), 21 (32), 11320-11324CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
Insertion of unsatd. systems such as alkynes and olefins into unactivated sp3 C-H bonds remains an unexplored problem. This issue was addressed by successfully incorporating a wide variety of functionalized alkynes and electron-deficient olefins into the unactivated sp3 C-H bond of pivalic acid derivs. with excellent syn- and linear- selectivity. A strongly chelating 8-aminoquinoline directing group proved beneficial for these insertion reactions, while an air-stable and inexpensive Ni(II) salt was employed as the active catalyst.
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(d) Liu, Y.-H.; Liu, Y.-J.; Yan, S.-Y.; Shi, B.-F. Ni(II)-catalyzed dehydrative alkynylation of unactivated (hetero)aryl C–H bonds using oxygen: a user-friendly approach. Chem. Commun. 2015, 51, 11650– 11653, DOI: 10.1039/C5CC03729H
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20d
Ni(II)-catalyzed dehydrative alkynylation of unactivated (hetero)aryl C-H bonds using oxygen: a user-friendly approach
Liu, Yan-Hua; Liu, Yue-Jin; Yan, Sheng-Yi; Shi, Bing-Feng
Chemical Communications (Cambridge, United Kingdom) (2015), 51 (58), 11650-11653CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Ni(II)-catalyzed dehydrative alkynylation of unactivated C(sp2)-H bonds with terminal alkynes under atm. pressure of oxygen was developed. This reaction features the use of catalytic amts. of nickel as the catalyst and O2 as the sole oxidant, providing a user-friendly approach to the synthesis of aryl alkynes.
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21
For C–H functionalization reactions where alkyne or alkene act as hydrogen acceptor, see:
(a) Inoue, S.; Shiota, H.; Fukumoto, Y.; Chatani, N. Ruthenium-Catalyzed Carbonylation at Ortho C–H Bonds in Aromatic Amides Leading to Phthalimides: C–H Bond Activation Utilizing a Bidentate System. J. Am. Chem. Soc. 2009, 131, 6898– 6899, DOI: 10.1021/ja900046z
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21a
Ruthenium-Catalyzed Carbonylation at Ortho C-H Bonds in Aromatic Amides Leading to Phthalimides: C-H Bond Activation Utilizing a Bidentate System
Inoue, Satoshi; Shiota, Hirotaka; Fukumoto, Yoshiya; Chatani, Naoto
Journal of the American Chemical Society (2009), 131 (20), 6898-6899CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A new type of carbonylation of the ortho C-H bonds in arom. amides, e.g., I, in which the pyridin-2-ylmethylamino moiety functions as a bidentate directing group, can be achieved to generate phthalimide derivs. such as II. The presence of ethylene as a hydrogen acceptor and also of H2O, probably for the generation of an active catalytic species, is required. A wide variety of functional groups, including methoxy, amino, ester, ketone, cyano, chloro, and even bromo substituents, are tolerated as substituents on the arom. amides. A dinuclear ruthenium complex contg. two amide ligands was isolated by the stoichiometric reaction of I and Ru3(CO)12, in which I binds to one Ru atom in the expected N,N fashion and the carbonyl oxygen binds to the other Ru atom as an O donor.
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(b) Hasegawa, N.; Charra, V.; Inoue, S.; Fukumoto, Y.; Chatani, N. Highly Regioselective Carbonylation of Unactivated C(sp3)–H Bonds by Ruthenium Carbonyl. J. Am. Chem. Soc. 2011, 133, 8070– 8073, DOI: 10.1021/ja2001709
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21b
Highly Regioselective Carbonylation of Unactivated C(sp3)-H Bonds by Ruthenium Carbonyl
Hasegawa, Nao; Charra, Valentine; Inoue, Satoshi; Fukumoto, Yoshiya; Chatani, Naoto
Journal of the American Chemical Society (2011), 133 (21), 8070-8073CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The regioselective carbonylation of unactivated C(sp3)-H bonds of aliph. amides was achieved using Ru3(CO)12 as a catalyst. The presence of a 2-pyridinylmethylamine moiety in the amide is crucial for a successful reaction. The reaction shows a preference for C-H bonds of Me groups as opposed to methylene C-H bonds and tolerates a variety of functional groups. The stoichiometric reaction of an amide with Ru3(CO)12 gave a dinuclear ruthenium complex in which the 2-pyridinylmethylamino moiety was coordinated to the ruthenium center in an N,N manner.
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(c) Song, W.; Ackermann, L. Nickel-catalyzed alkyne annulation by anilines: versatile indole synthesis by C–H/N–H functionalization. Chem. Commun. 2013, 49, 6638– 6640, DOI: 10.1039/c3cc43915a
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21c
Nickel-catalyzed alkyne annulation by anilines: versatile indole synthesis by C-H/N-H functionalization
Song, Weifeng; Ackermann, Lutz
Chemical Communications (Cambridge, United Kingdom) (2013), 49 (59), 6638-6640CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
Versatile nickel catalysts enabled the step-economical synthesis of decorated indoles through alkyne annulations with anilines bearing removable directing groups. E.g., in presence of Ni(cod)2 and dppf, annulation of PhC≡CPh with N-(2-pyrimidinyl)aniline gave 81% indole deriv. (I). The C-H/N-H activation strategy efficiently occurred in the absence of any metal oxidants and with excellent selectivities.
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(d) Obata, A.; Ano, Y.; Chatani, N. Nickel-catalyzed C–H/N–H annulation of aromatic amides with alkynes in the absence of a specific chelation system. Chem. Sci. 2017, 8, 6650– 6655, DOI: 10.1039/C7SC01750B
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21d
Nickel-catalyzed C-H/N-H annulation of aromatic amides with alkynes in the absence of a specific chelation system
Obata, Atsushi; Ano, Yusuke; Chatani, Naoto
Chemical Science (2017), 8 (9), 6650-6655CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
The Ni-catalyzed reaction of arom. amides 4-H3COC6H4NHC(O)R (R = 4-fluorophenyl, 1-naphthyl, 2-furyl, etc.) with alkynes such as diphenylacetylene, 1-phenyl-1-propyne, 4-octyne, etc. in the presence of KOBut involves C-H/N-H oxidative annulation to give 1(2H)-isoquinolinones, e.g., I. A key to the success of the reaction is the use of a catalytic amt. of strong base, such as KOBut. The reaction shows a high functional group compatibility. The reaction with unsym. alkynes, such as 1-arylalkynes, gives the corresponding 1(2H)-isoquinolinones with a high level of regioselectivity. This discovery would lead to the development of Ni-catalyzed chelation-assisted C-H functionalization reactions without the need for a specific chelation system.
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For Rh-catalyzed C–H functionalization with internal alkyne, see:
(a) Mochida, S.; Nobuyoshi, U.; Koji, H.; Tetsuya, S.; Masahiro, M. Rhodium-catalyzed Oxidative Coupling/Cyclization of Benzamides with Alkynes via C–H Bond Cleavage. Chem. Lett. 2010, 39, 744– 746, DOI: 10.1246/cl.2010.744
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22a
Rhodium-catalyzed oxidative coupling/cyclization of benzamides with alkynes via C-H bond cleavage
Mochida, Satoshi; Umeda, Nobuyoshi; Hirano, Koji; Satoh, Tetsuya; Miura, Masahiro
Chemistry Letters (2010), 39 (7), 744-746CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
An oxidative coupling of primary, secondary, and tertiary benzamides with internal alkynes proceeds efficiently under rhodium catalysis was studied and the synthesis of the target compds. was achieved selectively providing the corresponding 1:1 and 1:2 coupling products, accompanied by C-H and/or N-H bond cleavages. Some of the products exhibit intense fluorescence in the solid state. The products thus obtained included N,N-dimethyl-5,6,7,8-tetraphenyl-1-naphthalenecarboxamide, 5,6,13-triphenyl-8H-dibenzo[a,g]quinolizin-8-one derivs. and 2,3,4-triphenyl-1(2H)-isoquinolinone derivs.
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(b) Hyster, T. K.; Rovis, T. Rhodium-Catalyzed Oxidative Cycloaddition of Benzamides and Alkynes via C–H/N–H Activation. J. Am. Chem. Soc. 2010, 132, 10565– 10569, DOI: 10.1021/ja103776u
[ ACS Full Text ], [ CAS], Google Scholar
22b
Rhodium-Catalyzed Oxidative Cycloaddition of Benzamides and Alkynes via C-H/N-H Activation
Hyster, Todd K.; Rovis, Tomislav
Journal of the American Chemical Society (2010), 132 (30), 10565-10569CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The oxidative cycloaddn. of benzamides and alkynes has been developed. The reaction utilizes Rh(III) catalysts in the presence of Cu(II) oxidants, and is proposed to proceed by N-H metalation of the amide followed by ortho C-H activation. The resultant rhodacycle undergoes alkyne insertion to form isoquinolones in good yield. The reaction is tolerant of extensive substitution on the amide, alkyne, and arene, including halides, silyl ethers, and unprotected aldehydes as substituents. Unsym. alkynes proceed with excellent regioselectivity, and heteroaryl carboxamides are tolerated leading to intriguing scaffolds for medicinal chem. A series of competition expts. shed further light on the mechanism of the transformation and reasons for selectivity.
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(c) Guimond, N.; Gorelsky, S. I.; Fagnou, K. Rhodium(III)-Catalyzed Heterocycle Synthesis Using an Internal Oxidant: Improved Reactivity and Mechanistic Studies. J. Am. Chem. Soc. 2011, 133, 6449– 6457, DOI: 10.1021/ja201143v
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22c
Rhodium(III)-Catalyzed Heterocycle Synthesis Using an Internal Oxidant: Improved Reactivity and Mechanistic Studies
Guimond, Nicolas; Gorelsky, Serge I.; Fagnou, Keith
Journal of the American Chemical Society (2011), 133 (16), 6449-6457CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Directing groups that can act as internal oxidants have recently been shown to be beneficial in metal-catalyzed heterocycle syntheses that undergo C-H functionalization. Pursuant to the rhodium(III)-catalyzed redox-neutral isoquinolone synthesis that we recently reported, we present in this article the development of a more reactive internal oxidant/directing group that can promote the formation of a wide variety of isoquinolones at room temp. while employing low catalyst loadings (0.5 mol %). In contrast to previously reported oxidative rhodium(III)-catalyzed heterocycle syntheses, the new conditions allow for the first time the use of terminal alkynes. Also, it is shown that the use of alkenes, including ethylene, instead of alkynes leads to the room temp. formation of 3,4-dihydroisoquinolones. Mechanistic investigations of this new system point to a change in the turnover limiting step of the catalytic cycle relative to the previously reported conditions. Concerted metalation-deprotonation (CMD) is now proposed to be the turnover limiting step. In addn., DFT calcns. conducted on this system agree with a stepwise C-N bond reductive elimination/N-O bond oxidative addn. mechanism to afford the desired heterocycle. Concepts highlighted by the calcns. were found to be consistent with exptl. results.
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(d) Hyster, T. K.; Rovis, T. An improved catalyst architecture for rhodium(III) catalyzed C–H activation and its application to pyridone synthesis. Chem. Sci. 2011, 2, 1606– 1610, DOI: 10.1039/C1SC00235J
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22d
An improved catalyst architecture for rhodium(III) catalyzed C-H activation and its application to pyridone synthesis
Hyster, Todd K.; Rovis, Tomislav
Chemical Science (2011), 2 (8), 1606-1610CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
The authors have developed a method for prepg. pyridones from the coupling reaction of acrylamides and alkynes with either stoichiometric Cu(OAc)2 or catalytic Cu(OAc)2 and air as oxidants. In these studies, a larger ligand, 1,3-di-tert-butylcyclopentadienyl (termed Cpt) results in higher degrees of regioselectivity in the alkyne insertion event. The transformation tolerates a broad variety of alkynes and acrylamides. Also, Cpt and Cp* demonstrate similar catalytic activity. This similarity allows for mechanistic studies to be undertaken which suggest a difference in mechanism between this reaction and the previously studied benzamide system.
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(e) Shan, G.; Flegel, J.; Li, H.; Merten, C.; Ziegler, S.; Antonchick, A. P.; Waldmann, H. C–H Bond Activation for the Synthesis of Heterocyclic Atropisomers Yields Hedgehog Pathway Inhibitors. Angew. Chem., Int. Ed. 2018, 57, 14250– 14254, DOI: 10.1002/anie.201809680
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22e
C-H Bond Activation for the Synthesis of Heterocyclic Atropisomers Yields Hedgehog Pathway Inhibitors
Shan, Gang; Flegel, Jana; Li, Houhua; Merten, Christian; Ziegler, Slava; Antonchick, Andrey P.; Waldmann, Herbert
Angewandte Chemie, International Edition (2018), 57 (43), 14250-14254CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
In the presence of a nonracemic cyclopentenopyridine rhodium complex, O-(arylpentynyl) arylhydroxamates such as I underwent enantioselective C-H activation and cyclization reactions mediated by dibenzoyl peroxide and CsOAc in 2-chloroethanol/1,2-dichloroethane to yield atropisomeric arylisoquinolinones such as II in 45-95% yields and in 78:22-96:4 er. Five of the arylisoquinolinone products (including II) inhibited the Hedgehog pathway in human cells; one of the compds. tested inhibited the Hedgehog pathway but did not displace labeled cyclopamine from Smoothened, implying that at least one of the arylisoquinolinones does not inhibit the Hedgehog pathway through binding to Smoothened.
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(f) Shibata, K.; Natsui, S.; Chatani, N. Rhodium-Catalyzed Alkenylation of C–H Bonds in Aromatic Amides with Alkynes. Org. Lett. 2017, 19, 2234– 2237, DOI: 10.1021/acs.orglett.7b00709
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22f
Rhodium-Catalyzed Alkenylation of C-H Bonds in Aromatic Amides with Alkynes
Shibata, Kaname; Natsui, Satoko; Chatani, Naoto
Organic Letters (2017), 19 (9), 2234-2237CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
The rhodium-catalyzed alkenylation of C-H bonds of arom. amides with alkynes is reported. A variety of functional groups, including OMe, OAc, Br, Cl, and even NO2, are applicable to this reaction to give the corresponding hydroarylation products. The presence of an 8-aminoquinoline group as the directing group is crucial for the success of the reaction.
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23
For Ru-catalyzed C–H functionalization with internal alkynes, see:
(a) Allu, S.; Swamy, K. C. K. Ruthenium-Catalyzed Synthesis of Isoquinolones with 8-Aminoquinoline as a Bidentate Directing Group in C–H Functionalization. J. Org. Chem. 2014, 79, 3963– 3972, DOI: 10.1021/jo500424p
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23a
Ruthenium-Catalyzed Synthesis of Isoquinolones with 8-Aminoquinoline as a Bidentate Directing Group in C-H Functionalization
Allu, Srinivasarao; Swamy, K. C. Kumara
Journal of Organic Chemistry (2014), 79 (9), 3963-3972CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
Ruthenium-catalyzed oxidative annulation of N-quinolin-8-yl-benzamides with alkynes in open air has been achieved using 8-aminoquinolinyl moiety as a bidentate directing group in the presence of Cu(OAc)2·H2O as an oxidant. This reaction offers a broad substrate scope, and both sym. and unsym. alkynes can be applied. High regioselectivity was achieved in the case of unsym. (aryl)alkynes. Reaction with heteroaryl amides was also successful in this catalytic process. A ruthenium-N-quinolin-8-yl-benzamide complex was isolated in the absence of alkyne; in the absence of both N-quinolin-8-yl-benzamide and alkyne, in contrast to literature, only the monoacetate complex RuCl(OAc)(p-cymene), but not the bis-acetate complex Ru(OAc)2(p-cymene), was isolated. These data suggest that this reaction may proceed via N,N-bidentate chelate complex. Key products were characterized by X-ray crystallog.
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(b) Kaishap, P. P.; Duarah, G.; Chetiab, D.; Gogoi, S. Ru(II)-Catalyzed annulation of benzamidines and alkynes by C–H/N–H activation: a facile synthesis of 1-aminoisoquinolines. Org. Biomol. Chem. 2017, 15, 3491– 3498, DOI: 10.1039/C7OB00389G
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23b
Ru()-Catalyzed annulation of benzamidines and alkynes by C-H/N-H activation: a facile synthesis of 1-aminoisoquinolines
Kaishap, P. P.; Duarah, G.; Chetia, D.; Gogoi, S.
Organic & Biomolecular Chemistry (2017), 15 (16), 3491-3498CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
An inexpensive Ru(II) complex catalyzes the oxidative annulation reaction of disubstituted alkynes with benzamidines to provide highly valuable 1-aminoisoquinolines in high yields. The reaction also features excellent regioselectivity with some unsym. alkynes.
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24
For Pd-catalyzed C–H functionalization with internal alkynes, see:
(a) Shu, Z.; Guo, Y.; Li, W.; Wang, B. Pd/C-catalyzed synthesis of N-aryl and N-alkyl isoquinolones via CH/NH activation. Catal. Today 2017, 297, 292– 297, DOI: 10.1016/j.cattod.2017.02.005
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24a
Pd/C-catalyzed synthesis of N-aryl and N-alkyl isoquinolones via C-H/N-H activation
Shu, Zhen; Guo, Yuntao; Li, Wei; Wang, Baiquan
Catalysis Today (2017), 297 (), 292-297CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)
Pd/C-catalyzed direct synthesis of N-aryl and N-alkyl isoquinolones was developed via the annulation reactions of benzamides and alkynes in high yields (up to 99%) through the cleavage of C-H/N-H bonds. The reaction was ligand-free and air was used as oxidant. High regioselectivities were found when unsym. alkynes or meta-benzamides were used as substrates. The heterocyclic carboxamide substrates, such as furan and thiophene derivs., also afforded the corresponding products in high yields.
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(b) Sharma, N.; Saha, R.; Parveen, N.; Sekar, G. Palladium-Nanoparticles-Catalyzed Oxidative Annulation of Benzamides with Alkynes for the Synthesis of Isoquinolones. Adv. Synth. Catal. 2017, 359, 1947– 1958, DOI: 10.1002/adsc.201601137
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24b
Palladium-Nanoparticles-Catalyzed Oxidative Annulation of Benzamides with Alkynes for the Synthesis of Isoquinolones
Sharma, Nidhi; Saha, Rajib; Parveen, Naziya; Sekar, Govindasamy
Advanced Synthesis & Catalysis (2017), 359 (11), 1947-1958CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
A novel method to synthesize isoquinolones I (R1 = H, 6,7-(CH3)2, 6-OC2H5, etc.; R2 = CH3, C2H5, CH2C6H5; R3 = R4 = C6H5, 4-H3CC6H4, 3-FC6H4, etc.; R3 = C6H5, 4-H3CC6H4, 4-CH3OC6H4; R4 = CH3, C6H5) via oxidative annulation of N-alkoxy benzamides and alkynes using binaphthyl-stabilized palladium nanoparticles (Pd-BNP) as catalyst has been developed. This methodol. affords various isoquinolone derivs. in good to excellent yields with high regioselectivities in the presence of air as oxidant. N-Methoxybenzothioamide was also found to underwent oxidative annulation with alkyne successfully and provided a sulfur analog of isoquinolones II (R1 = R2 = H, 3-CH3, 3-F, 4-F) in moderate yields. The Pd-BNP catalyst was easily recovered and reused up to four times without any apparent agglomeration.
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25
For Co-catalyzed C–H functionalization with internal alkyne, see:
(a) Grigorjeva, L.; Daugulis, O. Cobalt-catalyzed, aminoquinoline-directed C(sp²)-H bond alkenylation by alkynes. Angew. Chem., Int. Ed. 2014, 53, 10209– 10212, DOI: 10.1002/anie.201404579
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25a
Cobalt-catalyzed, aminoquinoline-directed C(sp2)-H bond alkenylation by alkynes
Grigorjeva, Liene; Daugulis, Olafs
Angewandte Chemie, International Edition (2014), 53 (38), 10209-10212CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
A method for Co-catalyzed, aminoquinoline- and picolinamide-directed C(sp2)H bond alkenylation by alkynes was developed. The method shows excellent functional-group tolerance and both internal and terminal alkynes are competent substrates for the coupling. The reaction employs a Co(OAc)2.4H2O catalyst, Mn(OAc)2 co-catalyst, and O2 (from air) as a terminal oxidant.
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(b) Nguyen, T. T.; Grigorjeva, L.; Daugulis, O. Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp2 C–H Bonds. ACS Catal. 2016, 6, 551– 554, DOI: 10.1021/acscatal.5b02391
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25b
Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp2 C-H Bonds
Nguyen, Tung Thanh; Grigorjeva, Liene; Daugulis, Olafs
ACS Catalysis (2016), 6 (2), 551-554CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
In this paper, authors introduce arylphosphinic acid aminoquinoline amides as competent substrates for cobalt-catalyzed sp2 C-H bond functionalization. Specifically, the feasibility of their coupling with alkynes, alkenes, and allyl pivalate has been demonstrated. Reactions are catalyzed by simple Co(NO3)2 hydrate in ethanol or mixed dioxane/tBuOH solvent in the presence of Mn(OAc)3·2H2O additive, sodium pivalate, or acetate base and use oxygen from the air as an oxidant. Directing group removal affords ortho-functionalized P,P-diarylphosphinic acids.
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(c) Manoharan, R.; Jeganmohan, M. Cobalt-catalyzed cyclization of benzamides with alkynes: a facile route to isoquinolones with hydrogen evolution. Org. Biomol. Chem. 2018, 16, 8384– 8389, DOI: 10.1039/C8OB01924J
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25c
Cobalt-catalyzed cyclization of benzamides with alkynes: a facile route to isoquinolones with hydrogen evolution
Manoharan Ramasamy; Jeganmohan Masilamani
Organic & biomolecular chemistry (2018), 16 (37), 8384-8389 ISSN:.
The reaction of benzamides with alkynes assisted by an 8-aminoquinoline ligand in the presence of Co(OAc)2·4H2O and pivalic acid under an air atmosphere provided isoquinolone derivatives in good to excellent yields. In this reaction, the active Co(iii) species is regenerated by the reaction of Co(i) species with pivalic acid under an air atmosphere with hydrogen evolution. The proposed mechanism was supported by competition experiments, deuterium labelling studies, radical scavenger experiments and kinetic studies.
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(d) Zhai, S.; Qiu, S.; Chen, X.; Wu, J.; Zhao, H.; Tao, C.; Li, Y.; Cheng, B.; Wang, H.; Zhai, H. 2-(1-Methylhydrazinyl)pyridine as a reductively removable directing group in a cobalt-catalyzed C(sp2)–H bond alkenylation/annulation cascade. Chem. Commun. 2018, 54, 98– 101, DOI: 10.1039/C7CC08533H
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25d
2-(1-Methylhydrazinyl)pyridine as a reductively removable directing group in a cobalt-catalyzed C(sp2)-H bond alkenylation/annulation cascade
Zhai, Shengxian; Qiu, Shuxian; Chen, Xiaoming; Wu, Jiang; Zhao, Hua; Tao, Cheng; Li, Yun; Cheng, Bin; Wang, Huifei; Zhai, Hongbin
Chemical Communications (Cambridge, United Kingdom) (2018), 54 (1), 98-101CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
We describe a new application of 2-(1-methylhydrazinyl)pyridine as a bidentate directing group to directing cobalt-catalyzed C(sp2)-H alkenylation/annulation of the corresponding benzoic hydrazides to form an isoquinoline backbone, via reacting with a terminal or internal alkyne followed by annulation. The reaction shows a broad substrate scope with the products obtained in good to excellent yields and high regioselectivity. Moreover, the directing group can be reductively removed in one step under mild conditions.
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In the presence of a strong base, such as t-BuOK, N–H deprotonation would form a nickel(0) ate complex. A recent computational study indicates the subsequent C–H metalation from the nickel(0) ate complex occurs via a ligand-to-ligand hydrogen transfer mechanism. See ref (8c).
There is no corresponding record for this reference.
27
For select reviews and crystal structures of Ni-hydride complexes, see:
(a) Eberhardt, N. A.; Guan, H. Nickel Hydride Complexes. Chem. Rev. 2016, 116, 8373– 8426, DOI: 10.1021/acs.chemrev.6b00259
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27a
Nickel Hydride Complexes
Eberhardt, Nathan A.; Guan, Hairong
Chemical Reviews (Washington, DC, United States) (2016), 116 (15), 8373-8426CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review; nickel hydride complexes, defined herein as any mols. bearing a nickel hydrogen bond, are crucial intermediates in numerous nickel-catalyzed reactions. Some of them are also synthetic models of nickel-contg. enzymes such as [NiFe]-hydrogenase. The overall objective of this review is to provide a comprehensive overview of this specific type of hydride complexes, which has been studied extensively in recent years. This review begins with the significance and a very brief history of nickel hydride complexes, followed by various methods and spectroscopic or crystallog. tools used to synthesize and characterize these complexes. Also discussed are stoichiometric reactions involving nickel hydride complexes and how some of these reactions are developed into catalytic processes.
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(b) Matson, E. M.; Martinez, G. E.; Ibrahim, A. D.; Jackson, B. J.; Bertke, J. A.; Fout, A. R. Nickel(II) Pincer Carbene Complexes: Oxidative Addition of an Aryl C–H Bond to Form a Ni(II) Hydride. Organometallics 2015, 34, 399– 407, DOI: 10.1021/om5007177
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27b
Nickel(II) Pincer Carbene Complexes: Oxidative Addition of an Aryl C-H Bond to Form a Ni(II) Hydride
Matson, Ellen M.; Espinosa Martinez, Gabriel; Ibrahim, Abdulrahman D.; Jackson, Bailey J.; Bertke, Jeffrey A.; Fout, Alison R.
Organometallics (2015), 34 (2), 399-407CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
The synthesis and characterization of a series of nickel(II) pincer complexes of the meta-phenylene-bridged bis-N-heterocyclic DIPPCCC ligand framework are reported. Characterization of the Ni(II)Cl complex revealed a square planar species with Cl- and the anionic carbon trans to one another. Formation of Ni(II) alkyl complexes derived from complex 1 was accomplished by addn. of LiR [R = CH3 (2); CH2SiMe3 (3)]. Furthermore, we report a synthetic pathway to access the catalytically relevant Ni(II)H species (DIPPCCC)NiH (4), by direct oxidative addn. of an aryl C-H bond across a Ni(0) center. Complexes 1-4 have been characterized by 1H and 13C NMR and electronic absorption spectroscopies as well as x-ray crystallog.
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(c) Clement, N. D.; Cavell, K. J.; Jones, C.; Elsevier, C. J. Oxidative Addition of Imidazolium Salts to Ni0 and Pd0: Synthesis and Structural Characterization of Unusually Stable Metal–Hydride Complexes. Angew. Chem., Int. Ed. 2004, 43, 1277
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27c
Oxidative addition of imidazolium salts to Ni0 and Pd0: Synthesis and structural characterization of unusually stable metal-hydride complexes
Clement, Nicolas D.; Cavell, Kingsley J.; Jones, Cameron; Elsevier, Cornelis J.
Angewandte Chemie, International Edition (2004), 43 (10), 1277-1279CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
C-H activation of imidazolium salts by coordinatively unsatd. low-valent Ni and Pd complexes occurs under mild conditions. Surprisingly stable hydrido-metal-N-heterocyclic carbene complexes were isolated, which demonstrates the ease with which imidazolium-based ionic liqs. may react with transition-metal complexes during catalysis. Thus, reaction of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene with Ni(COD)2 in PhMe followed by treatment with 1-butyl-3-methylimidazolium tetrafluoroborate gave 73% title complex, [NiH(bmiy)(dmesiy)2]BF4 (3b), whereas reaction of 1,3-dimethylimidazolium tetrafluoroborate with bis[1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene]palladium in THF/Me2CO gave 62% [PdH(dmiy)(dmesiy)2]BF4 (5). The crystal structures of 3b and 5 were detd.
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Crabtree, R. H. Dihydrogen Complexation. Chem. Rev. 2016, 116, 8750– 8769, DOI: 10.1021/acs.chemrev.6b00037
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28
Dihydrogen Complexation
Crabtree, Robert H.
Chemical Reviews (Washington, DC, United States) (2016), 116 (15), 8750-8769CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review; dihydrogen complexation with retention of the H-H bond, once an exotic concept, has by now appeared in a very wide range of contexts. Three structural types are currently recognized: Kubas dihydrogen, stretched dihydrogen, and compressed dihydrides. These can be difficult to distinguish, hence the development of a no. of novel spectroscopic methods for doing so, mainly based on NMR spectroscopy. Three important reactivity patterns are identified: proton loss, oxidative addn., and dissocn., each of which often contributes to larger reaction schemes, as in homogeneous hydroformylation. Main group examples are beginning to appear, although here it is mainly by computational studies that the relevant structures can be identified. Enzymes such as the hydrogenases and nitrogenases are also proposed to involve these structures.
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(a) She, L.; Li, X.; Sun, H.; Ding, J.; Frey, M.; Klein, H.-F. Insertion of Alkynes into Ni–H Bonds: Synthesis of Novel Vinyl Nickel(II) and Dinuclear Vinyl Nickel(II) Complexes Containing a [P, S]-Ligand. Organometallics 2007, 26, 566– 570, DOI: 10.1021/om0606340
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29a
Insertion of Alkynes into Ni-H Bonds: Synthesis of Novel Vinyl Nickel(II) and Dinuclear Vinyl Nickel(II) Complexes Containing a [P, S]-Ligand
She, Lei; Li, Xiaoyan; Sun, Hongjian; Ding, Jun; Frey, Markus; Klein, Hans-Friedrich
Organometallics (2007), 26 (3), 566-570CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Reactions of alkynes with Ni hydride complexes bearing a [P, S]-ligand and supported by trimethylphosphine were studied. Tetracoordinate vinyl Ni(II) complexes [(L)Ni[C(:CH2)Ph]PMe3] (3; LH = o-Ph2PC6H4SH), [(L)Ni[C(:CH2)SiMe3]PMe3] (5) and [(L)Ni[C(:CH2)Bu]PMe3] (6) with square-planar geometry were obtained in 47-64% yields by reaction of phenylacetylene, trimethylsilylacetylene, and 1-hexyne with the hydrido Ni complex [(L)Ni(PMe3)2H] (1), resp. Reaction of 1,4-bis(trimethylsilylethynyl)benzene with complex 1 proceeds as a mono-insertion and afforded 76% [(L)Ni[C(:CHSiMe3)C6H4C≡CSiMe3-p]PMe3] (7) as a 4:1 mixt. of Z and E isomers, while reaction of 1,4-bis(ethynyl)benzene with 1 leads to the dinuclear vinyl Ni(II) complex [p-(L)Ni(PMe3)C(:CH2)C6H4C(:CH2)Ni(L)PMe3] (8) in 30% yield.
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(b) Zhou, H.; Sun, H.; Zheng, T.; Zhang, S.; Li, X. Synthesis of Vinylnickel and Nickelacyclopropane Complexes Containing a Chelate [P,Se]-Ligand. Eur. J. Inorg. Chem. 2015, 3139– 3145, DOI: 10.1002/ejic.201500293
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29b
Synthesis of vinylnickel and nickelacyclopropane complexes containing a chelate [P,Se]-ligand
Zhou, Hongwei; Sun, Hongjian; Zheng, Tingting; Zhang, Shumiao; Li, Xiaoyan
European Journal of Inorganic Chemistry (2015), 2015 (19), 3139-3145CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
Nickel(II) selenolate hydride complex [Ph2P(1,2-C6H4)SeNiH(PMe3)2] (1) was prepd. by oxidative addn. of 2-(diphenylphosphino)benzeneselenol 2-Ph2PC6H4SeH with Ni(PMe3)4. The insertion reactions of 1 with alkynes RC≡CR1 gave vinylnickel complexes [Ph2P(1,2-C6H4)SeNi(CR:CHR1)(PMe3)] (2, R = Ph, R1 = H; 3, R = Me, R1 = Ph). The phosphoranylidene-substituted nickelacyclopropane complexes [(2-Ph2PC6H4Se)Ni(Me3P:CPh-CHPh)] (4), [(2-Ph2PC6H4Se)Ni(Me3P:CTMS-CH2)] (5) [(2-Ph2PC6H4Se)Ni(Me3P:CPh-CHTMS)] (6A) and [(2-Ph2PC6H4Se)Ni(Me3P:CTMS-CHPh)] (6B), contg. an ylidic ligand were obtained by reacting diphenylacetylene, (trimethylsilyl)acetylene, and 1-phenyl-2-(trimethylsilyl)acetylene with 1. The mol. structures of 1-5 were detd. by single-crystal x-ray diffraction.
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(c) Xue, B.; Sun, H.; Ren, S.; Li, X.; Fuhr, O. Vinyl/Phenyl Exchange Reaction within Vinyl Nickel Complexes Bearing Chelate [P, S]-Ligands. Organometallics 2017, 36, 4246– 4255, DOI: 10.1021/acs.organomet.7b00671
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29c
Vinyl/Phenyl Exchange Reaction within Vinyl Nickel Complexes Bearing Chelate [P, S]-Ligands
Xue, Benjing; Sun, Hongjian; Ren, Shishuai; Li, Xiaoyan; Fuhr, Olaf
Organometallics (2017), 36 (21), 4246-4255CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Three Ni(II) hydrides, [2-Ph2P(4-Me-C6H3)S]NiH(PMe3)2 (1), [2-Ph2P(6-Me3Si-C6H3)S]NiH(PMe3)2 (2), and [2-Ph2P(4-Me3Si -C6H3)S]NiH(PMe3)2 (3), were synthesized via S-H bond activation through the reaction of Ni(PMe3)4 with (2-diphenylphosphanyl)thiophenols. The reactions of Ni(II) hydrides (1-3) with different alkynes were studied. Although the 1st step is the insertion of alkyne into the Ni-H bond for each reaction, different final products were isolated. Normal vinyl Ni complex [2-Ph2P(4-Me-C6H3)S]Ni(CPh:CH2)(PMe3) (4) was obtained by the reaction of phenylacetylene with 1. The nickelacyclopropane complexes [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CH2] (5), [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CH2] (6), [2-Ph2P(4-Me3-C6H3)S]Ni[Ph(PMe3)C-CHPh] (7), [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CHPh] (8), [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CHPh] (9), [2-Ph2P(4-Me-C6H3)S]Ni[Ph(PMe3)C-CHSiMe3] (10) or [2-Ph2P(4-Me-C6H3)S]Ni[Me3Si(PMe3)C-CHPh] (10), [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CHSiMe3] (11) or [2-Ph2P(6-Me3Si-C6H3)S]Ni[Me3Si(PMe3)C-CHPh] (11), and [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CHSiMe3] (12) or [2-Ph2P(4-Me3Si-C6H3)S]Ni[Me3Si(PMe3)C-CHPh] (12) contg. a ylidic ligand were formed by the reaction of phenylacetylene, diphenylacetylene, and 1-phenyl-2-(trimethylsilyl)acetylene with 1, 2, and 3, resp. The phenyl/vinyl exchange Ni(II) complexes [2-(PhCH2:CSiMe3)P(4-Me-C6H3)S]Ni(Ph)(PMe3) (13), [2-(PhCH2:CSiMe3)P(6-Me3Si-C6H3)S]Ni(Ph)(PMe3) (14), and [2-(PhCH2:CSiMe3)P(4-Me3Si-C6H3)S]Ni(Ph)(PMe3) (15) could be obtained by insertion of trimethylsilylacetylene into Ni-H bonds of 1, 2, and 3. This is a novel reaction type between alkyne and Ni hydride. Whether increasing the electronegativity on the benzene ring or on the alkyne leads to the instability of the vinyl Ni complex, and is beneficial to the C-P reductive elimination to form nickelacyclopropane complexes or Ph Ni complexes via vinyl/phenyl exchange reaction in the case of the more electroneg. Ni center. All the Ni complexes were fully detected by IR, NMR and the mol. structures of complexes 1, 2, 7, 9, 13, and 14 were confirmed by single crystal x-ray diffraction.
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30
An alternative pathway involving oxidative addition of ortho C(sp²)–H bond with the Ni(0) catalyst was considered computationally. The barrier of the C–H oxidative addition is 19.5 kcal/mol with respect to amide 1 and Ni(cod)₂. However, the subsequent steps in this pathway were highly disfavored. Both alkyne insertion into Ni–H bond and N–H deprotonation to form the five-membered Ni(II) metallacycle 9 require very high activation barriers of 44.5 and 67.2 kcal/mol with respect to 1 and Ni(cod)₂, respectively. Based on these results, this oxidative addition pathway was ruled out (see Supporting Information for more details).
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31
(a) Brookhart, M.; Green, M. L. H.; Parkin, G. Agostic interactions in transition metal compounds. Proc. Natl. Acad. Sci. USA 2007, 104, 6908– 6914, DOI: 10.1073/pnas.0610747104
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31a
Agostic interactions in transition metal compounds
Brookhart, Maurice; Green, Malcolm L. H.; Parkin, Gerard
Proceedings of the National Academy of Sciences of the United States of America (2007), 104 (17), 6908-6914CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
A review of the impact of agostic interactions (i.e., 3-center-2-electron M-H-C bonds) on the structures and reactivity of organotransition metal compds. is presented.
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(b) Jongbloed, L. S.; García-Lopez, D.; Heck, R. V.; Siegler, M. A.; Carbo, J. J.; Vlugt, J. I. V. D. Arene C(sp2)-H Metalation at NiII Modeled with a Reactive PONCPh Ligand. Inorg. Chem. 2016, 55, 8041– 8047, DOI: 10.1021/acs.inorgchem.6b01162
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31b
Arene C(sp2)-H metalation at NiII modeled with a reactive PONCPh ligand
Jongbloed, Linda S.; Garcia-Lopez, Diego; van Heck, Richard; Siegler, Maxime A.; Carbo, Jorge J.; van der Vlugt, Jarl Ivar
Inorganic Chemistry (2016), 55 (16), 8041-8047CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
Coordination of the reactive phosphinitopyridylphenyl PONCPh ligand, 6-Ph-2-tBu2PO-pyridine (HL) to NiBr2 initially yields paramagnetic brown [NiBr2(HL-κN,κP)] (1), but addn. of triethylamine results in fast and facile cyclometalation at NiII, giving [NiBr(κ3-P,N,C-L)] (2) as well-defined species. This is a rare example of direct cyclometalation at NiII from a C-H bond in a ligand structure other than encumbering ligands (e.g., ECE pincers). Diamagnetic yellow complex 2 protonates instantaneously in reaction with HBF4 to give purple [NiBr(κ3-P,N-HL)]BF4 (3). A very unusual (an)agostic Ni(CPh-H) interaction in the solid-state structure of 3 was unequivocally demonstrated using single-crystal x-ray crystallog. and was interpreted by d. functional theory calcns. (quantum theory of atoms in mols. and electron localization function anal.). These compds. may be viewed as models for key intermediates in the Ni-catalyzed C-H functionalization of arenes.
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(c) Lein, M. Characterization of agostic interactions in theory and computation. Coord. Chem. Rev. 2009, 253, 625– 634, DOI: 10.1016/j.ccr.2008.07.007
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31c
Characterization of agostic interactions in theory and computation
Lein, Matthias
Coordination Chemistry Reviews (2009), 253 (5+6), 625-634CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
A review. Agostic interactions are covalent intramol. interactions between an electron deficient metal and a σ-bond in close geometrical proximity to the metal atom. While the classic cases involve CH σ-bonds close to early transition metals like Ti, many more agostic systems were proposed which contain CH, SiH, BH, CC, and SiC σ -bonds coordinated to a wide range of metal atoms. Recent computational studies of a multitude of agostic interactions are reviewed in this contribution. It is highlighted how several difficulties with the theor. description of the phenomenon arise because of the relative weakness of this interaction. The methodol. used to compute and interpret agostic interactions is presented and different approaches such as atoms in mols. (AIMs), natural bonding orbitals (NBOs) or the electron localization function (ELF) are compared and put into context. A brief overview of the history and terminol. of agostic interactions is given in the introduction and fundamental differences between α-, β-, and other agostic interactions are explained.
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(d) Etienne, M.; Weller, A. S. Intramolecular C–C agostic complexes: C–C sigma interactions by another name. Chem. Soc. Rev. 2014, 43, 242– 259, DOI: 10.1039/C3CS60295H
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31d
Intramolecular C-C agostic complexes: C-C sigma interactions by another name
Etienne, Michel; Weller, Andrew S.
Chemical Society Reviews (2014), 43 (1), 242-259CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
A review of the developments in the synthesis, characterization and reactivity of complexes (s-, d- and f-block) in which a C-C single bond interacts with a metal center are discussed: so called C-C···M agostic complexes. Such species are of significant interest with regard to structure and bonding, the activation of C-C single bonds and, thus, catalytic methods of C-C bond formation (or activation). Examples of C-C agostic complexes of early and later transition metals, actinides and Group 1 metals are discussed, along with C-C agostic interactions in metallacyclobutanes. Examples of Si-Si···M, B-C···M and B-B···M agostic interactions are also presented. Throughout, the structural, spectroscopic and computational markers that indicate the likely presence of a C-C···M agostic interaction in a complex are highlighted.
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(e) Beattie, D. D.; Bowes, E. G.; Drover, M. W.; Love, J. A.; Schafer, L. L. Oxidation State Dependent Coordination Modes: Accessing an Amidate-Supported Nickel(I) δ-bis(C–H) Agostic Complex. Angew. Chem. 2016, 128, 13484– 13489, DOI: 10.1002/ange.201607243
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(f) Crabtree, R. H. Sigma Bonds as Ligand Donor Groups in Transition Metal Complexes. The Chemical Bond III; Mingos, D.M.P., Ed.; Springer International Publishing: Switzerland, 2015; Vol. 171, pp 63– 78.
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32
An alternatively pathway to form intermediate 11 from phosphine-bound Ni(II)-hydride complex 5 via σ-bond metathesis followed by PPh₃ decomplexation requires a much higher barrier (66.0 kcal/mol with respect to aromatic amide 1 and Ni(cod)₂ catalyst). This very high barrier is due to the absence of an agostic interaction and unfavorable steric effects of the additional PPh₃ ligand.
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33
PPh₃ coordination to intermediate 8 forms an off-cycle phosphine-bound alkenyl-Ni(II) complex 7. Complex 7 is 11.2 kcal/mol more stable than 8.
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34
(a) Another mechanism for C–H metalation involves σ-bond metathesis of the Ni–N bond in intermediate 8 with the ortho C–H bond to form a five-membered alkenyl-nickelacycle (see Supporting Information for details). This process requires an activation barrier of 39 kcal/mol with respect to the separate reactants and Ni(cod)₂, and thus can be ruled out.
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(b) In our calculations, we could not locate neither the transition state structure for the oxidative addition of the ortho C(sp²)–H bond from alkenyl-Ni(II) complex 8 nor the resulting Ni(IV)-hydride complex. All attempts to locate these structures resulted in TS3, 8, or 9. Intrinsic reaction coordinate (IRC) calculations were carried out for TS3 to confirm that it connects to complexes 8 and 9.
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35
We also computationally considered the use of cis-2-butene rather than 2-butyne as the H₂ acceptor to promote the C–H metalation. In this alternatively pathway, the barrier of σ-bond metathesis is 34.8 kcal/mol with respect to the separate reactants and Ni(cod)₂, and thus this pathway is less favorable than that using alkyne as H₂ acceptor (see Supporting Information for details).
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36
McCarren, P. R.; Liu, P.; Cheong, P. H.-Y.; Jamison, T. F.; Houk, K. N. Mechanism and Transition-State Structures for Nickel-Catalyzed Reductive Alkyne–Aldehyde Coupling Reactions. J. Am. Chem. Soc. 2009, 131, 6654– 6655, DOI: 10.1021/ja900701g
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36
Mechanism and Transition-State Structures for Nickel-Catalyzed Reductive Alkyne-Aldehyde Coupling Reactions
McCarren, P. R.; Liu, Peng; Cheong, Paul Ha-Yeon; Jamison, Timothy F.; Houk, K. N.
Journal of the American Chemical Society (2009), 131 (19), 6654-6655CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
The mechanism of nickel-catalyzed reductive alkyne-aldehyde coupling reactions has been investigated using d. functional theory. The preferred mechanism involves oxidative cyclization to form the nickeladihydrofuran intermediate followed by transmetalation and reductive elimination. The rate- and selectivity-detg. oxidative cyclization transition state is analyzed in detail. The d → π*.perp. back-donation stabilizes the transition state and leads to higher reactivity for alkynes than alkenes. Strong Lewis acids accelerate the couplings with both alkynes and alkenes by coordinating with the aldehyde oxygen in the transition state.
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In addition, the N in 2-pyridinylmethylamine is a better donor that electronically promotes the reductive elimination via TS6.
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38
Liang, L.-C.; Pin-Shu Chien, P.-S.; Lee, P.-Y. Phosphorus and Olefin Substituent Effects on the Insertion Chemistry of Nickel(II) Hydride Complexes Containing Amido Diphosphine Ligands. Organometallics 2008, 27, 3082– 3093, DOI: 10.1021/om701294a
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38
Phosphorus and olefin substituent effects on the insertion chemistry of nickel(II) hydride complexes containing amido diphosphine ligands
Liang, Lan-Chang; Chien, Pin-Shu; Lee, Pei-Ying
Organometallics (2008), 27 (13), 3082-3093CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
Ni(II) hydride complexes supported by amido diphosphine ligands, including sym. [N(o-C6H4PR2)2]- ([R-PNP]-; R = Ph, iPr, Cy) and unsym. [N(o-C6H4PPh2)(o-C6H4PiPr2)]- ([Ph-PNP-iPr]-), were prepd. for the study of olefin insertion chem. The unsym. ligand precursor H[Ph-PNP-iPr] (1d) that features different substituents (Ph and isopropyl) at the two P donors was prepd. in 53% yield as colorless crystals. Treatment of Ni(COD)2 (COD = cycloocta-1,5-diene) with H[R-PNP] (R = Ph (1a), iPr (1b), Cy (1c)) or 1d produced the corresponding four-coordinate Ni hydride complexes 2a-d. Attempts to isolate 2a led instead to the cyclooct-4-en-1-yl complex [Ph-PNP]Ni(η1-C8H13) (3a) as a consequence of COD insertion into the Ni-H bond of 2a. The reactions of 2a,d with ethylene, 1-hexene, and norbornene, resp., generated cleanly the corresponding Et (4a,d), n-hexyl (5a,d), and 2-norbornyl (6a,d) complexes. The quant. formation of 5a,d is indicative of exclusive 1,2-insertion of 1-hexene. In contrast, styrene inserts into the Ni-H bond of 2d in an exclusively 2,1-manner to afford [Ph-PNP-iPr]NiCH(Me)Ph (7d) quant. The selective 2,1-insertion products [Ph-PNP]NiCH(Me)CO2Me (8a), [iPr-PNP]NiCH(Me)CO2Me (8b), [Cy-PNP]NiCH(Me)CO2Me (8c), and [Ph-PNP-iPr]NiCH(Me)CO2Me (8d) were also isolated from the reactions of Me acrylate with the corresponding Ni hydride complexes 2a-d. The effects of the P and olefin substituents on the reactivity and regioselectivity of the olefin insertion reactions are discussed. In addn. to soln. NMR spectroscopic data for all new compds., x-ray structures of 1d, 2b-d, 3a, and 5d-7d are reported.
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(a) Kogut, E.; Zeller, A.; Warren, T. H.; Strassner, T. Structure and Dynamics of Neutral β-H Agostic Nickel Alkyls: A Combined Experimental and Theoretical Study. J. Am. Chem. Soc. 2004, 126, 11984– 11994, DOI: 10.1021/ja0477221
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39a
Structure and Dynamics of Neutral β-H Agostic Nickel Alkyls: A Combined Experimental and Theoretical Study
Kogut, Elzbieta; Zeller, Alexander; Warren, Timothy H.; Strassner, Thomas
Journal of the American Chemical Society (2004), 126 (38), 11984-11994CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Addn. of BF3·OEt2 to ethereal solns. of the Ni(II) β-diketiminates [Me2NN]Ni(R)(2,4-lutidine) (Me2NN = 2,6-Me2C6H3N:CMeCHC(Me):NC6H3Me2-2,6; R = Et (1), Pr (2)) gave the neutral β-H agostic monoalkyls [Me2NN]Ni(R) (R = Et (3), Pr (4)). X-ray studies of primary alkyls 3 and 4a reveal acute Ni-Cα-Cβ angles with short Ni-Cβ distances, indicating structures along the β-H elimination pathway. Positional disorder of the alkyl group in the x-ray structure of 4 corresponds to partial (22%) occupancy by the secondary alkyl [Me2NN]Ni(CHMe2) (4b). Variable-temp. NMR spectra of 3 and 4 reveal fluxional behavior that result from β-H elimination, in-plane rotation of the β-CH3 group, and a tetrahedral triplet structure for 3 that were studied by d. functional theory calcns. at the Becke3LYP/6-31G* level of theory without simplifications on the β-diketiminate ancillary ligand. Calcns. support low temp. NMR studies that identify the linear β-H agostic Pr isomer 4a as the ground state with the branched β-H agostic isomer 4b slightly higher in energy. NMR studies and calcns. show that the β-agostic 3 reluctantly coordinates ethene and that 3 is the ground state for this ethylene oligomerization catalyst. The thermodn. isotope effect KH/KD = 1.3(2) measured for the loss of 2,4-lutidine from 1 to form β-agostic 3 was also examd. by DFT calcns.
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(b) Scherer, W.; Herz, V.; Brück, A.; Hauf, C.; Reiner, F.; Altmannshofer, S.; Leusser, D.; Stalke, D. The Nature of β-Agostic Bonding in Late-Transition-Metal Alkyl Complexes. Angew. Chem., Int. Ed. 2011, 50, 2845– 2849, DOI: 10.1002/anie.201006065
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39b
The nature of β-agostic bonding in late-transition-metal alkyl complexes
Scherer, Wolfgang; Herz, Verena; Brueck, Andreas; Hauf, Christoph; Reiner, Florian; Altmannshofer, Sandra; Leusser, Dirk; Stalke, Dietmar
Angewandte Chemie, International Edition (2011), 50 (12), 2845-2849, S2845/1-S2845/62CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Nickel(II) diphosphine cycloalkyl complexes [(dtbpe)NiR][BF4] [2b-d, dtbpe = 1,2-bis(di-tert-butylphosphino)ethane, R = norbornyl, dicyclopentadien-8-yl, 3,4-dihydrodicyclopentadien-8-yl], featuring increased steric bulk of the cycloalkyl group and hindered rotation of agostic β-CH fragment, were prepd. and studied by NMR spectroscopy and theor. calcns.; comparison is made with highly-fluxional Et deriv. [(dtbpe)NiEt][BF4] (2a). Proton NMR chem. shifts were calcd. for 2b-d and compared to exptl. values. Both exptl. and theor. charge d. maps reveal a stable Cβ-Hβ bond path, however, showing a significantly decreased charge d. Accordingly, the complexes 2 feature short Ni-Hβ distances (1.671 Å) with a significant electron d. accumulation at the Ni-Hβ crit. point. Both upfield and downfield shifts of the agostic proton are obsd., depending on the particular charge distribution around the nickel center and bond geometry.
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Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. Universal Solvation Model Based on Solute Electron Density and on a Continuum Model of the Solvent Defined by the Bulk Dielectric Constant and Atomic Surface Tensions. J. Phys. Chem. B 2009, 113, 6378– 6396, DOI: 10.1021/jp810292n
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Universal Solvation Model Based on Solute Electron Density and on a Continuum Model of the Solvent Defined by the Bulk Dielectric Constant and Atomic Surface Tensions
Marenich, Aleksandr V.; Cramer, Christopher J.; Truhlar, Donald G.
Journal of Physical Chemistry B (2009), 113 (18), 6378-6396CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
We present a new continuum solvation model based on the quantum mech. charge d. of a solute mol. interacting with a continuum description of the solvent. The model is called SMD, where the "D" stands for "d." to denote that the full solute electron d. is used without defining partial at. charges. "Continuum" denotes that the solvent is not represented explicitly but rather as a dielec. medium with surface tension at the solute-solvent boundary. SMD is a universal solvation model, where "universal" denotes its applicability to any charged or uncharged solute in any solvent or liq. medium for which a few key descriptors are known (in particular, dielec. const., refractive index, bulk surface tension, and acidity and basicity parameters). The model separates the observable solvation free energy into two main components. The first component is the bulk electrostatic contribution arising from a self-consistent reaction field treatment that involves the soln. of the nonhomogeneous Poisson equation for electrostatics in terms of the integral-equation-formalism polarizable continuum model (IEF-PCM). The cavities for the bulk electrostatic calcn. are defined by superpositions of nuclear-centered spheres. The second component is called the cavity-dispersion-solvent-structure term and is the contribution arising from short-range interactions between the solute and solvent mols. in the first solvation shell. This contribution is a sum of terms that are proportional (with geometry-dependent proportionality consts. called at. surface tensions) to the solvent-accessible surface areas of the individual atoms of the solute. The SMD model has been parametrized with a training set of 2821 solvation data including 112 aq. ionic solvation free energies, 220 solvation free energies for 166 ions in acetonitrile, methanol, and DMSO, 2346 solvation free energies for 318 neutral solutes in 91 solvents (90 nonaq. org. solvents and water), and 143 transfer free energies for 93 neutral solutes between water and 15 org. solvents. The elements present in the solutes are H, C, N, O, F, Si, P, S, Cl, and Br. The SMD model employs a single set of parameters (intrinsic at. Coulomb radii and at. surface tension coeffs.) optimized over six electronic structure methods: M05-2X/MIDI!6D, M05-2X/6-31G*, M05-2X/6-31+G**, M05-2X/cc-pVTZ, B3LYP/6-31G*, and HF/6-31G*. Although the SMD model has been parametrized using the IEF-PCM protocol for bulk electrostatics, it may also be employed with other algorithms for solving the nonhomogeneous Poisson equation for continuum solvation calcns. in which the solute is represented by its electron d. in real space. This includes, for example, the conductor-like screening algorithm. With the 6-31G* basis set, the SMD model achieves mean unsigned errors of 0.6-1.0 kcal/mol in the solvation free energies of tested neutrals and mean unsigned errors of 4 kcal/mol on av. for ions with either Gaussian03 or GAMESS.
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Abstract
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Scheme 1
Scheme 1. Mechanisms of Transition-Metal-Catalyzed C–H Functionalization of Amides Using N,N-Bidentate Directing Groups
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Scheme 2
Scheme 2. Ni-Catalyzed C–H Functionalization of Amides with Alkynes Using N,N-Bidentate Directing Groups
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Scheme 3
Scheme 3. Proposed Mechanisms of the Ni-Catalyzed Ortho C(sp²)–H Oxidative Cycloaddition Reaction
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Figure 1
Figure 1. Mechanisms of the C–H metalation steps in the reaction of amide 1 with 2-butyne. (a) Computed reaction energy profiles of Ni-catalyzed ortho C(sp²)–H metalation. (b) Optimized structures of σ-C–H complexes and σ-CAM transition states with select bond distances shown in Å. All energies are with respect to the separate reactants and Ni(cod)₂.
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Figure 2
Figure 2. Mechanisms of the C–C and C–N bond formation steps from the nickelacycle intermediate 9. (a) Computed reaction energy profiles of C–C and C–N bond formation mechanisms. (b) Optimized structures of transition states with select bond distances shown in Å. All energies are with respect to the separate reactants and Ni(cod)₂.
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Figure 3
Figure 3. Effects of directing group on the C–N bond reductive elimination. (a) C–N reductive elimination with 2-pyridinylmethylamine directing group. (b) C–N reductive elimination with 8-aminoquinoline directing group. (c) Optimized structures of C–N reductive elimination transition states with select bond distances in angstrom (Å) and bond angles shown in degree. All energies are with respect to the phosphine-bound seven-membered nickelacycles 15 and 20.
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Scheme 4
Scheme 4. Experimentally Observed Regioselectivity with Internal Aryl Alkynes(12)
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Figure 4
Figure 4. Regioselectivity-determining insertion transition states with (a) alkyne 23 and (b) alkyne 24.
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Figure 5
Figure 5. Reaction energy profile of the Ni(II)-hydride-catalyzed isomerization of cis-2-butene to trans-2-butene. All energies are with respect to the Ni(II)-hydride complex 5 and cis-2-butene.
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  A review. This review highlights 24 recent papers and illustrates their significance to the C-H functionalization endeavor. Some of the current trends are covered. E.g., design of new directing groups that are readily removed or converted into useful functionality, broadening the scope from the more traditional functionalization of sp2 C-H bonds to sp3 C-H bonds, application of the methodol. to a broader range of functionality, and modification of the directing influence away from just ortho-functionalization.
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2. 2
  (a) Zaitsev, V. G.; Shabashov, D.; Daugulis, O. Highly Regioselective Arylation of sp3 C–H Bonds Catalyzed by Palladium Acetate. J. Am. Chem. Soc. 2005, 127, 13154– 13155, DOI: 10.1021/ja054549f
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  2a
  Highly Regioselective Arylation of sp3 C-H Bonds Catalyzed by Palladium Acetate
  Zaitsev, Vladimir G.; Shabashov, Dmitry; Daugulis, Olafs
  Journal of the American Chemical Society (2005), 127 (38), 13154-13155CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A new palladium-catalyzed arylation process based on C-H activation has been developed. The utilization of pyridine-contg. directing groups allows the β-arylation of carboxylic acid derivs. and γ-arylation of amine derivs. Both primary and secondary sp3 C-H bonds, as well as sp2 C-H bonds, are reactive.
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  .
  (b) Nadres, E. T.; Santos, G. I. F.; Shabashov, D.; Daugulis, O. Scope and Limitations of Auxiliary-Assisted, Palladium-Catalyzed Arylation and Alkylation of sp2 and sp3 C–H Bonds. J. Org. Chem. 2013, 78, 9689– 9714, DOI: 10.1021/jo4013628
  [ ACS Full Text ], [ CAS], Google Scholar
  2b
  Scope and Limitations of Auxiliary-Assisted, Palladium-Catalyzed Arylation and Alkylation of sp2 and sp3 C-H Bonds
  Nadres, Enrico T.; Santos, Gerson Ivan Franco; Shabashov, Dmitry; Daugulis, Olafs
  Journal of Organic Chemistry (2013), 78 (19), 9689-9714CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  The scope of palladium-catalyzed, auxiliary-assisted direct arylation and alkylation of sp2 and sp3 C-H bonds of amine and carboxylic acid derivs. has been investigated. The method employs a palladium acetate catalyst, substrate, aryl, alkyl, benzyl, or allyl halide, and inorg. base in tert-amyl alc. or water solvent at 100-140 °C. Aryl and alkyl iodides as well as benzyl and allyl bromides are competent reagents in this transformation. The picolinic acid auxiliary is used for amine γ-functionalization, and the 8-aminoquinoline auxiliary is used for carboxylic acid β-functionalization. Some optimization of base, additives, and solvent is required for achieving best results.
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  (c) Daugulis, O.; Roane, J.; Tran, L. D. Bidentate, Monoanionic Auxiliary-Directed Functionalization of Carbon–Hydrogen Bonds. Acc. Chem. Res. 2015, 48, 1053– 1064, DOI: 10.1021/ar5004626
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  2c
  Bidentate, Monoanionic Auxiliary-Directed Functionalization of Carbon-Hydrogen Bonds
  Daugulis, Olafs; Roane, James; Tran, Ly Dieu
  Accounts of Chemical Research (2015), 48 (4), 1053-1064CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
  A review. In recent years, carbon-hydrogen bond functionalization has evolved from an organometallic curiosity to a tool used in mainstream applications in the synthesis of complex natural products and drugs. The use of C-H bonds as a transformable functional group is advantageous because these bonds are the most abundant functionality in org. mols. One-step conversion of these bonds to the desired functionality shortens synthetic pathways, saving reagents, solvents, and labor. Less chem. waste is generated as well, showing that this chem. is environmentally beneficial. This Account describes the development and use of bidentate, monoanionic auxiliaries for transition-metal-catalyzed C-H bond functionalization reactions. The chem. was initially developed to overcome the limitations with palladium-catalyzed C-H bond functionalization assisted by monodentate directing groups. By the use of electron-rich bidentate directing groups, functionalization of unactivated sp3 C-H bonds under palladium catalysis has been developed. Furthermore, a no. of abundant base-metal complexes catalyze functionalization of sp2 C-H bonds. At this point, aminoquinoline, picolinic acid, and related compds. are among the most used and versatile directing moieties in C-H bond functionalization chem. These groups facilitate catalytic functionalization of sp2 and sp3 C-H bonds by iron, cobalt, nickel, copper, ruthenium, rhodium, and palladium complexes. Exceptionally general reactivity is obsd., enabling, among other transformations, direct arylation, alkylation, fluorination, sulfenylation, amination, etherification, carbonylation, and alkenylation of carbon-hydrogen bonds. The versatility of these auxiliaries can be attributed to the following factors. First, they are capable of stabilizing high oxidn. states of transition metals, thereby facilitating the C-H bond functionalization step. Second, the directing groups can be removed, enabling their use in synthesis and functionalization of natural products and medicinally relevant substances. While the development of these directing groups presents a significant advance, several limitations of this methodol. are apparent. The use of expensive second-row transition metal catalysts is still required for efficient sp3 C-H bond functionalization. Furthermore, the need to install and subsequently remove the relatively expensive directing group is a disadvantage.
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3. 3
  For reviews on chelation-assisted C–H functionalization, see:
  (a) Rouquet, G.; Chatani, N. Catalytic Functionalization of C(sp2)–H and C(sp3)–H Bonds by Using Bidentate Directing Groups. Angew. Chem., Int. Ed. 2013, 52, 11726– 11743, DOI: 10.1002/anie.201301451
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  3a
  Catalytic functionalization of C(sp2)-H and C(sp3)-H bonds by using bidentate directing groups
  Rouquet, Guy; Chatani, Naoto
  Angewandte Chemie, International Edition (2013), 52 (45), 11726-11743CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. C-H bonds are ubiquitous in org. compds. It would, therefore, appear that direct functionalization of substrates by activation of C-H bonds would eliminate the multiple steps and limitations assocd. with the prepn. of functionalized starting materials. Regioselectivity is an important issue because org. mols. can contain a wide variety of C-H bonds. The use of a directing group can largely overcome the issue of regiocontrol by allowing the catalyst to come into proximity with the targeted C-H bonds. A wide variety of functional groups have been evaluated for use as directing groups in the transformation of C-H bonds. In 2005, Daugulis reported the arylation of unactivated C(sp3)-H bonds by using 8-aminoquinoline and picolinamide as bidentate directing groups, with Pd(OAc)2 as the catalyst. Encouraged by these promising results, a no. of transformations of C-H bonds have since been developed by using systems based on bidentate directing groups. In this review, recent advances in this area are discussed.
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  (b) Rit, R. K.; Yadav, M. R.; Ghosh, K.; Sahoo, A. K. Reusable directing groups [8-aminoquinoline, picolinamide, sulfoximine] in C(sp3)–H bond activation: present and future. Tetrahedron 2015, 71, 4450– 4459, DOI: 10.1016/j.tet.2015.03.085
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  3b
  Reusable directing groups [8-aminoquinoline, picolinamide, sulfoximine] in C(sp3)-H bond activation: present and future
  Rit, Raja K.; Yadav, M. Ramu; Ghosh, Koushik; Sahoo, Akhila K.
  Tetrahedron (2015), 71 (26-27), 4450-4459CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)
  A review. This report briefly discusses the reusable directing group assisted functionalization of unactivated remote alkyl C-H bonds and their synthetic potential in org. chem. The challenges involved for the functionalization of inert alkyl C-H bonds is highlighted. With the strong impact of C-H activation, we believe this report would boost researchers unraveling novel methods for the chemo-, regio-, and stereoselective activation of unbiased C(sp3)-H bonds and their potential utility for the rapid synthesis of complex mol. entities.
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  (c) Yang, X.; Shan, G.; Wang, L.; Rao, Y. Recent advances in transition metal (Pd, Ni)-catalyzed C(sp3)–H bond activation with bidentate directing groups. Tetrahedron Lett. 2016, 57, 819– 836, DOI: 10.1016/j.tetlet.2016.01.009
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  3c
  Recent advances in transition metal (Pd, Ni)-catalyzed C(sp3)-H bond activation with bidentate directing groups
  Yang, Xinglin; Shan, Gang; Wang, Liguo; Rao, Yu
  Tetrahedron Letters (2016), 57 (8), 819-836CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
  A review with refs. In recent years, transition metal-catalyzed C(sp3)-H functionalization has gradually emerged as a practical and powerful tool to prep. highly valuable chems. In this mini-review, we will give some examples to cover recent research advances on transition-metal (Pd, Ni) catalyzed C(sp3)-H functionalization via bidentate directing group coordination. Different bidentate directing groups will be discussed. As the whole field of transition metal-catalyzed C(sp3)-H functionalization keeps moving forward, more synthetically useful chemo-, regio-, diastereo-, and enantioselective reactions catalyzed by transition-metal with bidentate directing group coordination will be discovered in the future and this promising and attractive strategy will play a more crit. role in modern org. synthesis.
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  (d) He, R.; Huang, Z.-T.; Zheng, Q.-Y.; Wang, C. Isoquinoline skeleton synthesis via chelation-assisted C–H activation. Tetrahedron Lett. 2014, 55, 5705– 5713, DOI: 10.1016/j.tetlet.2014.08.077
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  3d
  Isoquinoline skeleton synthesis via chelation-assisted C-H activation
  He, Ruoyu; Huang, Zhi-Tang; Zheng, Qi-Yu; Wang, Congyang
  Tetrahedron Letters (2014), 55 (42), 5705-5713CODEN: TELEAY; ISSN:0040-4039. (Elsevier Ltd.)
  A review. Transition metal-catalyzed isoquinoline synthesis that profits from the strategy of chelation-assisted C-H activation has flourished over the past decade. By virtue of the directed C-H bond cleavage of imines, amines, amidines, oximes, hydroximoyl halides, hydrazones, or azines, diverse isoquinoline derivs. have been accessed from alkynes, conjugated dienes, or diazo compds. under the catalysis of rhodium, ruthenium, palladium, nickel, or manganese. This digest summarizes the annulation reactions via chelation-assisted C-H activation leading to isoquinolines, isoquinolinium salts, or isoquinoline N-oxides.
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4. 4
  For reviews on Ni-catalyzed C–H functionalization, see:
  (a) Tasker, S. Z.; Standley, E. A.; Jamison, T. F. Recent advances in homogeneous nickel catalysis. Nature 2014, 509, 299– 309, DOI: 10.1038/nature13274
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  Recent advances in homogeneous nickel catalysis
  Tasker, Sarah Z.; Standley, Eric A.; Jamison, Timothy F.
  Nature (London, United Kingdom) (2014), 509 (7500), 299-309CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
  A review. Tremendous advances have been made in nickel catalysis over the past decade. Several key properties of nickel, such as facile oxidative addn. and ready access to multiple oxidn. states, have allowed the development of a broad range of innovative reactions. In recent years, these properties have been increasingly understood and used to perform transformations long considered exceptionally challenging. Here we discuss some of the most recent and significant developments in homogeneous nickel catalysis, with an emphasis on both synthetic outcome and mechanism.
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  (b) Chatani, N. Nickel-Catalyzed C–H Bond Functionalization Utilizing an N,N′-Bidentate Directing Group. Top. Organomet. Chem. 2016, 56, 19– 46
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  Nickel-catalyzed C-H bond functionalization utilizing an N,N'-bidentate directing group
  Chatani, Naoto
  Topics in Organometallic Chemistry (2016), 56 (C-H Bond Activation and Catalytic Functionalization II), 19-46CODEN: TORCFV; ISSN:1616-8534. (Springer GmbH)
  This review discusses the use of nickel catalysts and N,N'-bidentate directing groups, such as 2-pyridinylmethylamine, 8-aminoquinoline, and derivs. thereof, which constitute a powerful combination for the chelation-assisted functionalization of C-H bonds.
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  (c) Aihara, Y.; Wuelbern, J.; Chatani, N. The Nickel(II)-Catalyzed Direct Benzylation, Allylation, Alkylation, and Methylation of CH Bonds in Aromatic Amides Containing an 8-Aminoquinoline Moiety as the Directing Group. Bull. Chem. Soc. Jpn. 2015, 88, 438– 446, DOI: 10.1246/bcsj.20140387
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  The nickel(II)-catalyzed direct benzylation, allylation, alkylation, and methylation of C-H bonds in aromatic amides containing an 8-aminoquinoline moiety as the directing group
  Aihara, Yoshinori; Wuelbern, Jendrik; Chatani, Naoto
  Bulletin of the Chemical Society of Japan (2015), 88 (3), 438-446CODEN: BCSJA8; ISSN:0009-2673. (Chemical Society of Japan)
  Direct alkylation via the cleavage of the ortho C-H bonds by a nickel-catalyzed reaction of arom. amides contg. an 8-aminoquinoline moiety as the directing group with alkyl halides is reported. Various alkyl halides, including benzyl, allyl, alkyl, and Me halides (or pseudo halides) participate as electrophilic coupling partners. The reaction shows a high functional group compatibility. The reaction proceeds in a highly regioselective manner at the less hindered C-H bonds in the reaction of meta-substituted arom. amides, irresp. of the electronic nature of the substituent. The mechanism responsible for the C-H alkylation reaction is discussed based on the results obtained in a variety of mechanistic expts.
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  (d) Castro, L. C. M.; Chatani, N. Nickel Catalysts/N,N′-Bidentate Directing Groups: An Excellent Partnership in Directed C–H Activation Reactions. Chem. Lett. 2015, 44, 410– 421, DOI: 10.1246/cl.150024
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  Nickel catalysts/N,N'-bidentate directing groups: an excellent partnership in directed C-H activation reactions
  Castro, Luis C. Misal; Chatani, Naoto
  Chemistry Letters (2015), 44 (4), 410-421CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
  A review. This review focuses on chelation-assisted regioselective C-H activation with C-C or/and C-N bond formation using Nickel(0) or -(II) as the catalysts, where bidentate directing groups play a key role in the successful transformation. A 2-pyridinylmethylamine or an 8-aminoquinoline moiety are the more powerful auxiliaries among the directing groups examd.
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  (e) Cai, X.; Xie, B. Recent advances in nickel-catalyzed C–H bond functionalized reactions. ARKIVOC 2015, i, 184, DOI: 10.3998/ark.5550190.p008.915
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  (f) Yamaguchi, J.; Muto, K.; Itami, K. Nickel-Catalyzed Aromatic C-H Functionalization. Top. Curr. Chem. 2016, 374, 55, DOI: 10.1007/s41061-016-0053-z
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  Nickel-Catalyzed Aromatic C-H Functionalization
  Yamaguchi Junichiro; Muto Kei; Itami Kenichiro; Itami Kenichiro
  Topics in current chemistry (Cham) (2016), 374 (4), 55 ISSN:2365-0869.
  Catalytic C-H functionalization using transition metals has received significant interest from organic chemists because it provides a new strategy to construct carbon-carbon bonds and carbon-heteroatom bonds in highly functionalized, complex molecules without pre-functionalization. Recently, inexpensive catalysts based on transition metals such as copper, iron, cobalt, and nickel have seen more use in the laboratory. This review describes recent progress in nickel-catalyzed aromatic C-H functionalization reactions classified by reaction types and reaction partners. Furthermore, some reaction mechanisms are described and cutting-edge syntheses of natural products and pharmaceuticals using nickel-catalyzed aromatic C-H functionalization are presented.
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  (g) Yamaguchi, J.; Muto, K.; Itami, K. Recent Progress in Nickel-Catalyzed Biaryl Coupling. Eur. J. Org. Chem. 2013, 19– 30, DOI: 10.1002/ejoc.201200914
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  Recent progress in nickel-catalyzed biaryl coupling
  Yamaguchi, Junichiro; Muto, Kei; Itami, Kenichiro
  European Journal of Organic Chemistry (2013), 2013 (1), 19-30CODEN: EJOCFK; ISSN:1099-0690. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review. Nickel catalysis for biaryl coupling reactions has received significant attention as a less expensive and less toxic alternative to "std." palladium catalysis. Here we describe recent developments in nickel-catalyzed biaryl coupling methodol., along with mechanistic studies and applications. In particular we focus on nickel-catalyzed coupling reactions in which "unreactive" bonds such as C-H, C-O, and C-C bonds are converted into biaryl moieties.
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  (h) Khan, M. S.; Haque, A.; Al-Suti, M. K.; Raithby, P. R. Recent advances in the application of group-10 transition metal based catalysts in C-H activation and functionalization. J. Organomet. Chem. 2015, 793, 114– 133, DOI: 10.1016/j.jorganchem.2015.03.023
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  Recent advances in the application of group-10 transition metal based catalysts in C-H activation and functionalization
  Khan, Muhammad S.; Haque, Ashanul; Al-Suti, Mohammed K.; Raithby, Paul R.
  Journal of Organometallic Chemistry (2015), 793 (), 114-133CODEN: JORCAI; ISSN:0022-328X. (Elsevier B.V.)
  A review. The importance of C-H bond activation in a simple mol. to form a mol. with enhanced functionality can be easily understood from a study of biol. processes at a mol. level where, for example, a specific enzyme selectively activates a chem. inert C-H bond and functionalizes it to a useful product. This strategy is now being used for large scale industrial processes and has both social and environmental benefits. C-H bond functionalization is also of major importance in catalysis because of the possibility of constructing complex structural motifs from relatively simple precursors. However, functionalization of a chem. inert C-H bond needs specific catalysts or reaction conditions that can selectively activate a particular C-H bond, leaving others intact. To achieve this target, various metal catalyzed or mediated reactions have been employed. Keeping the growing importance of this emerging field in mind, we now present recent advances in the field of C-H activation and functionalization using group 10 transition metal catalysts. Attempts have also been made to discuss the future of group 10 transition metals in catalysis.
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  Nickel complexes for catalytic C-H bond functionalization
  Johnson, S. A.
  Dalton Transactions (2015), 44 (24), 10905-10913CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  A review. The direct catalytic functionalization of traditionally unreactive C-H bonds is an atom-economic transformation that has become increasingly important and commonplace in synthetic applications. In general, 2nd and 3rd row transition metal complexes are used as catalysts in these reactions, whereas the less costly and more abundant 1st row metal complexes have limited utility. This Perspective article summarizes progress from lab. towards understanding the fundamental issues that complicate the use of Ni complexes for catalytic C-H bond functionalization, as well as approaches to overcoming these limitations. In practice Ni complexes can functionalize C-H bonds by processes that, to date, were not obsd. with the heavier metals. An example is provided by the catalytic stannylation of C-H bonds with tributylvinyltin, Bu3SnCH=CH2, which produces ethylene as a byproduct.
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5. 5
  (a) Davies, D. L.; Donald, S. M. A.; Macgregor, S. A. Computational Study of the Mechanism of Cyclometalation by Palladium Acetate. J. Am. Chem. Soc. 2005, 127, 13754– 13755, DOI: 10.1021/ja052047w
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  Computational Study of the Mechanism of Cyclometalation by Palladium Acetate
  Davies, David L.; Donald, Steven M. A.; Macgregor, Stuart A.
  Journal of the American Chemical Society (2005), 127 (40), 13754-13755CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Various mechanisms for the cyclometalation of dimethylbenzylamine by Pd acetate were studied by DFT calcns. Contrary to previous suggestions, the rate-limiting step is the electrophilic attack of the Pd on an ortho arene C-H bond to form an agostic complex rather than a Wheland intermediate. The cyclometalated product is then formed by intramol. deprotonation by acetate via a six-membered transition state; this step has almost no activation barrier.
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  High-Yielding Palladium-Catalyzed Intramolecular Alkane Arylation: Reaction Development and Mechanistic Studies
  Lafrance, Marc; Gorelsky, Serge I.; Fagnou, Keith
  Journal of the American Chemical Society (2007), 129 (47), 14570-14571CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Palladium-catalyzed alkane arylation reactions with aryl halides are described for the prepn. of 2,2-dialkyl-dihydrobenzofuran substrates. These reactions occur in excellent yield and very high selectivity for the formation of one sole product arising from a reaction at nearby Me groups. Mechanistic and computational studies point to the involvement of a concerted, inner-sphere palladation-deprotonation pathway that is enabled by the presence of three-center agostic interactions at the transition state. This mechanism accurately predicts the exptl. obsd. kinetic isotope effect as well as the site selectivity and should be useful in the design of new reactions and catalysts.
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  (d) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. Analysis of the Concerted Metalation-Deprotonation Mechanism in Palladium-Catalyzed Direct Arylation Across a Broad Range of Aromatic Substrates. J. Am. Chem. Soc. 2008, 130, 10848– 10849, DOI: 10.1021/ja802533u
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  5d
  Analysis of the Concerted Metalation-Deprotonation Mechanism in Palladium-Catalyzed Direct Arylation Across a Broad Range of Aromatic Substrates
  Gorelsky, Serge I.; Lapointe, David; Fagnou, Keith
  Journal of the American Chemical Society (2008), 130 (33), 10848-10849CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The concerted metalation-deprotonation mechanism predicts relative reactivity and regioselectivity for a diverse set of arenes spanning the entire spectrum of known palladium-catalyzed direct arylation coupling partners. An anal. following an active strain model provides a more complete portrayal of the important arene/catalyst parameters leading to a successful coupling. The breadth of arenes whose reactivity can be predicted by the CMD mechanism indicates that it may be far more widespread than previously imagined.
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  .
  (e) Guihaumé, J.; Clot, E.; Eisenstein, O.; Perutz, R. N. Importance of palladium–carbon bond energies in direct arylation of polyfluorinated benzenes. Dalton Trans. 2010, 39, 10510– 10519, DOI: 10.1039/c0dt00296h
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  5e
  Importance of palladium-carbon bond energies in direct arylation of polyfluorinated benzenes
  Guihaume, Julie; Clot, Eric; Eisenstein, Odile; Perutz, Robin N.
  Dalton Transactions (2010), 39 (43), 10510-10519CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  Fagnou et al. reported direct arylation reactions that use palladium catalysts to couple Ar1-X to Ar2-H with the aid of a coordinated base. These reactions are particularly favorable for polyfluorinated arenes Ar2-H (see S. I. Gorelsky, D. Lapointe and K. Fagnou, J. Am. Chem. Soc. 2008, 130, 10848). In this paper, we show by means of a DFT anal. how the energetics and activation energies vary with fluorine substitution and examine the structures of intermediates and transition states. The reactant is modelled by Pd(OAc)(Ph)(PMe3)(DMA) (DMA = dimethylacetamide). The sequence consists of (a) replacement of DMA by arene, (b) Concerted Deprotonation Metalation (CMD), (c) decoordination of AcOH, (d) reductive elimination of biaryl. Many of the variations are dominated by the no. of fluorine substituents ortho to the C-H bond and fall into three groups labeled accordingly: Set0Fo, Set1Fo, and Set2Fo. In the first step a coordinated solvent is replaced by the arene. The arenes of Set0Fo and Set1Fo coordinate in a conventional η2-CH:CH mode, whereas the arenes of Set2Fo coordinate in an η1-CH mode assisted by an O···H-C hydrogen bond from the coordinated acetate. Both the energy barriers to CMD and the product energies fall into the three typical sets with the highest barrier and highest product energy being for Set0Fo. They correlate more satisfactorily with the variations in Pd-C bond energies than with the C-H acidities. The barriers to reductive elimination from Pd(Ph)(ArF)(PMe3)(AcOH) increase systematically from Set0Fo to Set2Fo as the Pd-C bond becomes stronger in a regular fashion from Set0Fo to Set2Fo. Again there is a strong correlation between the energy barriers to reductive elimination and the Pd-C bond energies. It is found overall that the key aspects of the reactions are: (a) the lowering of the energy of the CMD step by the ortho fluorine substituents, (b) the regioselective activation of C-H bonds ortho to fluorine which is also detd. at the CMD step, (c) the decoordination of AcOH, which maintains the transition state for reductive elimination at low Gibbs free energy. The presence of fluorine increases the effectiveness of the reaction in the sense of points a and b via the increasing strength of the palladium-carbon bond.
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  .
  (f) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. Analysis of the Palladium-Catalyzed (Aromatic)C–H Bond Metalation–Deprotonation Mechanism Spanning the Entire Spectrum of Arenes. J. Org. Chem. 2012, 77, 658– 668, DOI: 10.1021/jo202342q
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  5f
  Analysis of the Palladium-Catalyzed (Aromatic)C-H Bond Metalation-Deprotonation Mechanism Spanning the Entire Spectrum of Arenes
  Gorelsky, Serge I.; Lapointe, David; Fagnou, Keith
  Journal of Organic Chemistry (2012), 77 (1), 658-668CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  A comprehensive understanding of the C-H bond cleavage step by the concerted metalation-deprotonation (CMD) pathway is important in further development of cross-coupling reactions using different catalysts. Distortion-interaction anal. of the C-H bond cleavage over a wide range of (hetero)aroms. has been performed in an attempt to quantify the various contributions to the CMD transition state (TS). The (hetero)aroms. evaluated were divided in different categories to allow an easier understanding of their reactivity and to quantify activation characteristics of different arene substituents. The CMD pathway to the C-H bond cleavage for different classes of arenes is also presented, including the formation of pre-CMD intermediates and the anal. of bonding interactions in TS structures. The effects of remote C2 substituents on the reactivity of thiophenes were evaluated computationally and were corroborated exptl. with competition studies. We show that nucleophilicity of thiophenes, evaluated by Hammett σp parameters, correlates with each of the distortion-interaction parameters. In the final part of this manuscript, we set the initial equations that can assist in the development of predictive guidelines for the functionalization of C-H bonds catalyzed by transition metal catalysts.
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  .
  (g) Petit, A.; Flygare, J.; Miller, A. T.; Winkel, G.; Ess, D. H. Transition-State Metal Aryl Bond Stability Determines Regioselectivity in Palladium Acetate Mediated C–H Bond Activation of Heteroarenes. Org. Lett. 2012, 14, 3680– 3683, DOI: 10.1021/ol301521n
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  5g
  Transition-State Metal Aryl Bond Stability Determines Regioselectivity in Palladium Acetate Mediated C-H Bond Activation of Heteroarenes
  Petit, Alban; Flygare, Josh; Miller, Alex T.; Winkel, Gerrit; Ess, Daniel H.
  Organic Letters (2012), 14 (14), 3680-3683CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
  D. functional calcns. reveal that the stability of developing metal aryl bonds in Pd(II)-acetate C-H activation transition states dets. regioselectivity in arene and heteroarene compds. This kinetic-thermodn. connection explains the general preference for activation of the strongest C-H bond and provides the possibility for regioselectivity prediction.
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  .
  (h) Dang, Y.; Qu, S.; Nelson, J. W.; Pham, H. D.; Wang, Z.-X.; Wang, X. The Mechanism of a Ligand-Promoted C(sp3)–H Activation and Arylation Reaction via Palladium Catalysis: Theoretical Demonstration of a Pd(II)/Pd(IV) Redox Manifold. J. Am. Chem. Soc. 2015, 137, 2006– 2014, DOI: 10.1021/ja512374g
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  5h
  The Mechanism of a Ligand-Promoted C(sp3)-H Activation and Arylation Reaction via Palladium Catalysis: Theoretical Demonstration of a Pd(II)/Pd(IV) Redox Manifold
  Dang, Yanfeng; Qu, Shuanglin; Nelson, John W.; Pham, Hai D.; Wang, Zhi-Xiang; Wang, Xiaotai
  Journal of the American Chemical Society (2015), 137 (5), 2006-2014CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  D. functional theory (DFT) computations (BP86 and M06-L) have been utilized to elucidate the detailed mechanism of a palladium-catalyzed reaction involving pyridine-type nitrogen-donor ligands that significantly expands the scope of C(sp3)-H activation and arylation. The reaction begins with precatalyst initiation, followed by substrate binding to the Pd(II) center through an amidate auxiliary, which directs the ensuing bicarbonate-assisted C(sp3)-H bond activation producing five-membered-ring cyclopalladate(II) intermediates. These Pd(II) complexes further undergo oxidative addn. with iodobenzene to form Pd(IV) complexes, which proceed by reductive C-C elimination/coupling to give final products of arylation. The base-assisted C(sp3)-H bond cleavage is found to be the rate-detg. step, which involves hydrogen bond interactions. The mechanism unravels the intimate involvement of the added 2-picoline ligand in every phase of the reaction, explains the isolation of the cyclopalladate intermediates, agrees with the obsd. kinetic hydrogen isotope effect, and demonstrates the Pd(II)/Pd(IV) redox manifold.
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  (i) Dang, Y.; Deng, X.; Guo, J.; Song, C.; Hu, W.; Wang, Z.-X. Unveiling Secrets of Overcoming the “Heteroatom Problem” in Palladium-Catalyzed Aerobic C–H Functionalization of Heterocycles: A DFT Mechanistic Study. J. Am. Chem. Soc. 2016, 138, 2712– 2723, DOI: 10.1021/jacs.5b12112
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  5i
  Unveiling Secrets of Overcoming the "Heteroatom Problem" in Palladium-Catalyzed Aerobic C-H Functionalization of Heterocycles: A DFT Mechanistic Study
  Dang, Yanfeng; Deng, Xi; Guo, Jiandong; Song, Chunyu; Hu, Wenping; Wang, Zhi-Xiang
  Journal of the American Chemical Society (2016), 138 (8), 2712-2723CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Directed C-H functionalization of heterocycles through an exocyclic directing group (DG) is challenging due to the interference of the endocyclic heteroatom(s). Recently, the heteroatom problem was circumvented with the development of the protection-free Pd-catalyzed aerobic C-H functionalization of heterocycles guided by an exocyclic CONHOMe DG. The authors herein provide DFT mechanistic insights to facilitate the expansion of the strategy. The transformation proceeds as follows. First, the Pd2(dba)3 precursor interacts with t-BuNC (L, one of the substrates) and O2 to form the L2Pd(II)-η2-O2 peroxopalladium(II) species that can selectively oxidize N-methoxy amide (e.g., PyCONHOMe) substrate, giving an active L2Pd(II)X2 (X = PyCONOMe) species and releasing H2O2. After t-BuNC ligand migratory insertion followed by a 1,3-acyl migration and assocn. with another t-BuNC, L2Pd(II)X2 converts to a more stable C-amidinyl L2Pd(II)XX' (X' = PyCON(t-Bu)C=NOMe) species. Finally, L2Pd(II)XX' undergoes C-H activation and C-C reductive elimination, affording the product. The C-H activation is the rate-detg. step. The success of the strategy has three origins: (i) the N-methoxy amide DG can be easily oxidized in situ to generate the active L2Pd(II)X2 species via the oxidase pathway, thus preventing the destructive oxygenase pathway leading to stable t-BuNCO or the O-bridged dimeric Pd(II) species. The methoxy group in this amide DG greatly facilitates the oxidase pathway, and the tautomerization of N-methoxy amide to its imidic acid tautomer makes the oxidn. of the substrate even easier. (ii) The X group in L2Pd(II)X2 can serve as an internal base to promote the C-H activation via CMD (concerted metalation-deprotonation) mechanism. (iii) The strong coordination ability of t-BuNC substrate/ligand suppresses the conventional cyclopalladation pathway enabled by the coordination of an endocyclic heteroatom to the Pd-center.
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  (j) Davies, D. L.; Macgregor, S. A.; McMullin, C. L. Computational Studies of Carboxylate-Assisted C–H Activation and Functionalization at Group 8–10 Transition Metal Centers. Chem. Rev. 2017, 117, 8649– 8709, DOI: 10.1021/acs.chemrev.6b00839
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  5j
  Computational Studies of Carboxylate-Assisted C-H Activation and Functionalization at Group 8-10 Transition Metal Centers
  Davies, David L.; Macgregor, Stuart A.; McMullin, Claire L.
  Chemical Reviews (Washington, DC, United States) (2017), 117 (13), 8649-8709CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  Computational studies on carboxylate-assisted C-H activation and functionalization at group 8-10 transition metal centers are reviewed. This Review is organized by metal and will cover work published from late 2009 until mid-2016. A brief overview of computational work prior to 2010 is also provided, and this outlines the understanding of carboxylate-assisted C-H activation in terms of the "ambiphilic metal-ligand assistance" (AMLA) and "concerted metalation deprotonation" (CMD) concepts. Computational studies are then surveyed in terms of the nature of the C-H bond being activated (C(sp2)-H or C(sp3)-H), the nature of the process involved (intramol. with a directing group or intermol.), and the context (stoichiometric C-H activation or within a variety of catalytic processes). This Review aims to emphasize the connection between computation and expt. and to highlight the contribution of computational chem. to our understanding of catalytic C-H functionalization based on carboxylate-assisted C-H activation. Some opportunities where the interplay between computation and expt. may contribute further to the areas of catalytic C-H functionalization and applied computational chem. are identified.
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  (k) García-Cuadrado, D.; Braga, A. A. C.; Maseras, F.; Echavarren, A. M. Proton Abstraction Mechanism for the Palladium-Catalyzed Intramolecular Arylation. J. Am. Chem. Soc. 2006, 128, 1066– 1067, DOI: 10.1021/ja056165v
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  5k
  Proton Abstraction Mechanism for the Palladium-Catalyzed Intramolecular Arylation
  Garcia-Cuadrado, Domingo; Braga, Ataualpa A. C.; Maseras, Feliu; Echavarren, Antonio M.
  Journal of the American Chemical Society (2006), 128 (4), 1066-1067CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Under the usual conditions, the Pd-catalyzed arylation does not involve an electrophilic arom. substitution reaction. On the basis of DFT calcns., we propose a mechanism for the Pd-catalyzed arylation that involves a proton abstraction by a carbonate or related ligand and that provides a satisfactory explanation for the exptl. data.
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  (l) Lafrance, M.; Rowley, C. N.; Woo, T. K.; Fagnou, K. Catalytic Intermolecular Direct Arylation of Perfluorobenzenes. J. Am. Chem. Soc. 2006, 128, 8754– 8756, DOI: 10.1021/ja062509l
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  5l
  Catalytic Intermolecular Direct Arylation of Perfluorobenzenes
  Lafrance, Marc; Rowley, Christopher N.; Woo, Tom K.; Fagnou, Keith
  Journal of the American Chemical Society (2006), 128 (27), 8754-8756CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Penta-, tetra-, tri-, and difluorobenzenes undergo direct arylation with a wide range of aryl halides in high yield. Inverse reactivity is obsd. compared to the common electrophilic arom. substitution pathway since electron-deficient, C-H acidic arenes react preferentially. Computational studies indicate that C-H bond cleavage occurs via a concerted carbon-palladium and carbon-hydrogen bond cleaving event involving a carbonate or a bromide ligand. The reactions are rapid, require only a slight excess of the perfluoroarene reagent, and utilize com. available, air-stable catalyst precursors.
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  (m) Pascual, S.; Mendoza, P.; Braga, A. A. C.; Maseras, F.; Echavarren, A. M. Bidentate phosphines as ligands in the palladium-catalyzed intramolecular arylation: the intermolecular base-assisted proton abstraction mechanism. Tetrahedron 2008, 64, 6021– 6029, DOI: 10.1016/j.tet.2008.01.056
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  5m
  Bidentate phosphines as ligands in the palladium-catalyzed intramolecular arylation: the intermolecular base-assisted proton abstraction mechanism
  Pascual, Sergio; de Mendoza, Paula; Braga, Ataualpa A. C.; Maseras, Feliu; Echavarren, Antonio M.
  Tetrahedron (2008), 64 (26), 6021-6029CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)
  The palladium-catalyzed arylation of aryl bromides can be carried out in the presence of bidentate phosphines, such as dppm, dppe, dppf, and Xantphos under mild conditions. The exptl. results and the DFT calcns. fully support for this reaction a mechanism proceeding by an intermol. proton abstraction.
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  (n) Kefalidis, C. E.; Baudoin, O.; Clot, E. DFT study of the mechanism of benzocyclobutene formation by palladium-catalysed C(sp3)–H activation: role of the nature of the base and the phosphine. Dalton Trans. 2010, 39, 10528– 10535, DOI: 10.1039/c0dt00578a
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  5n
  DFT study of the mechanism of benzocyclobutene formation by palladium-catalysed C(sp3)-H activation: role of the nature of the base and the phosphine
  Kefalidis, Christos E.; Baudoin, Olivier; Clot, Eric
  Dalton Transactions (2010), 39 (43), 10528-10535CODEN: DTARAF; ISSN:1477-9226. (Royal Society of Chemistry)
  DFT(B3PW91) calcns. of the mechanism of the intramol. C(sp3)-H arylation of 2-bromo-tert-butylbenzene to form benzocyclobutene catalyzed by Pd(PR3) (R = Me, tBu) and a base (acetate, bicarbonate, carbonate) show that the preferred mechanism is highly dependent on the nature of the phosphine and the base used in the calcns. With the exptl. reagents (PtBu3 and carbonate) the rate-detg. step is C-H activation with the base coordinated trans to the C-H bond. An agostic interaction of a geminal C-H bond with respect to the bond to be cleaved induces a lowering of the activation barrier.
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  (o) Korenaga, T.; Suzuki, N.; Sueda, M.; Shimada, K. Ligand effect on direct arylation by CMD process. J. Organomet. Chem. 2015, 780, 63– 69, DOI: 10.1016/j.jorganchem.2014.12.017
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  Ligand effect on direct arylation by CMD process
  Korenaga, Toshinobu; Suzuki, Noriki; Sueda, Masayoshi; Shimada, Kazuaki
  Journal of Organometallic Chemistry (2015), 780 (), 63-69CODEN: JORCAI; ISSN:0022-328X. (Elsevier B.V.)
  The ligand effect of electron-poor phosphines in the concerted metalation-deprotonation (CMD) process for intramol. direct arylation was exptl. and theor. demonstrated. The ligand acceleration effect (LAE) for the intramol. direct arylation of 1-bromo-2-(phenoxymethyl)benzene increased in the following order: P(BFPy)3 > P{3,5-(CF3)2-C6H3}3 > PCy3 > P(3,4,5-F3-C6H2)3 > P(4-F-C6H4)3 = PPh3 » P(C6F5)3. The use of highly electron-poor P(BFPy)3 allowed the catalyst loading to be decreased up to 0.01 mol%. The LAE is roughly proportional to the electronic effect of the phosphine ligand. The LAE was not obsd. in the case of P(C6F5)3 because of its lack of coordination ability for Pd(OAc)2, as confirmed by 31P NMR spectroscopy. The donating PCy3 ligand showed a higher LAE than PPh3. The relative activation free energies (ΔG≠) of the CMD process calcd. by the d. functional theory (DFT) at the M06-2X/6-31G(d) level with LANL2DZ showed the same trend as the exptl. results. The LAE in CMD was further evaluated by DFT calcns. using two approaches: (1) fragment energy anal. and (2) evaluation of NBO deletion energy in transition states in CMD. The results of the first technique indicated that the conformational change in PCy3 results in increase of activation energy (ΔE≠) in compared with PAr3 systems. The use of the second technique clarified that the highly electron-poor P(BFPy)3 ligand stabilized the CAr→Pd interaction and the electron-donating PCy3 stabilized the O→H···CAr interaction in the transition state in CMD.
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  (p) Holstein, P. M.; Vogler, M.; Larini, P.; Pilet, G.; Clot, E.; Baudoin, O. Efficient Pd0-Catalyzed Asymmetric Activation of Primary and Secondary C–H Bonds Enabled by Modular Binepine Ligands and Carbonate Bases. ACS Catal. 2015, 5, 4300– 4308, DOI: 10.1021/acscatal.5b00898
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  5p
  Efficient Pd0-Catalyzed Asymmetric Activation of Primary and Secondary C-H Bonds Enabled by Modular Binepine Ligands and Carbonate Bases
  Holstein, Philipp M.; Vogler, Maria; Larini, Paolo; Pilet, Guillaume; Clot, Eric; Baudoin, Olivier
  ACS Catalysis (2015), 5 (7), 4300-4308CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  New binepine ligands were synthesized, and characterized and induce high diastereo- and enantioselectivity in the intramol. arylation of primary and secondary C(sp3)-H bonds, giving rise to fused cyclopentanes. The ligands were obtained as bench-stable phosphonium tetrafluoroborate salts that can be directly employed in catalysis. A ferrocenyl P-substituent on the ligand allows achievement of high stereoselectivities in combination with potassium carbonate for the arylation of primary C-H bonds under unprecedentedly low temp. (90 °C) and catalyst loading (1-2 mol % Pd/2-3 mol % ligand). Using a base-free precatalyst, carbonate is the active base and to provide higher stereoselectivities than acetate and pivalate. The more difficult arylation of secondary C-H bonds could also be achieved and required fine-tuning of the ligand structure and the carbonate countercation. This method gave fused tricyclic products contg. three adjacent stereocenters as single diastereoisomers and with moderate to high enantioselectivity. Exptl. data indicated that the enantiodetermining C-H activation step involves a monoligated species. DFT (PBE0-D3) calcns. were performed with a prototypical binepine ligand to understand the origin of the enantioselectivity. The preference for the major enantiomer was traced to the establishment of a more efficient network of weak attractive interactions between the phosphine ligand and the substrate.
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6. 6
  Gensch, T.; Hopkinson, M. N.; Glorius, F.; Wencel-Delord, J. Mild metal-catalyzed C–H activation: examples and concepts. Chem. Soc. Rev. 2016, 45, 2900– 2936, DOI: 10.1039/C6CS00075D
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  Mild metal-catalyzed C-H activation: examples and concepts
  Gensch, T.; Hopkinson, M. N.; Glorius, F.; Wencel-Delord, J.
  Chemical Society Reviews (2016), 45 (10), 2900-2936CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  A review. In this review, the current state of the art that have been made in field of mild C-H activation transformations reported since 2011 that proceed either at or below ambient temp., in the absence of strongly acidic or basic additives or without strong oxidants have been presented. Furthermore, by identifying and discussing the major strategies that have led to these improvements, this review will serve as a useful conceptual overview and inspire the next generation of mild C-H transformations.
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7. 7
  Perutz, R. N.; Sabo-Etienne, S. The σ-CAM Mechanism: σ-Complexes as the Basis of σ-Bond Metathesis at Late-Transition-Metal Centers. Angew. Chem., Int. Ed. 2007, 46, 2578– 2592, DOI: 10.1002/anie.200603224
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  The σ-CAM mechanism: σ complexes as the basis of σ-bond metathesis at late-transition-metal centers
  Perutz, Robin N.; Sabo-Etienne, Sylviane
  Angewandte Chemie, International Edition (2007), 46 (15), 2578-2592CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A review of σ complexes particularly with silane and borane ligands, in which a σ-H-E bond (E = H, B, Si, C) acts as a two-electron donor to the metal center is presented. Clues that it is possible to interconvert σ ligands without a change in oxidn. state derive from C-H activation reactions effecting isotope exchange and from dynamic rearrangements of σ-complexes (see frontispiece). Through these pathways, metathesis of M-E bonds can occur at late transition metals. This process of σ-complex-assisted metathesis, or σ-CAM, is distinct from the familiar σ-bond metathesis (typical for d0 metals and requiring no intermediate) and from oxidative-reductive elimination mechanisms (inherently requiring intermediates with changed oxidn. states and sometimes involving α complexes). There are examples of σ-CAM mechanisms in catalysis, esp. for alkane borylation and isotope exchange of alkanes. It may also occur in silylation and alkene hydrogenation.
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  (a) Guihaumé, J.; Halbert, S.; Eisenstein, O.; Perutz, R. N. Hydrofluoroarylation of Alkynes with Ni Catalysts. C–H Activation via Ligand-to-Ligand Hydrogen Transfer, an Alternative to Oxidative Addition. Organometallics 2012, 31, 1300– 1314, DOI: 10.1021/om2005673
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  Hydrofluoroarylation of alkynes with Ni catalysts. C-H activation via ligand-to-ligand hydrogen transfer, an alternative to oxidative addition
  Guihaume, Julie; Halbert, Stephanie; Eisenstein, Odile; Perutz, Robin N.
  Organometallics (2012), 31 (4), 1300-1314CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  The mechanism of the hydrofluoroarylation of alkynes, RC≡CR, by nickel phosphine complexes, described by Nakao et al., was studied by d. functional theory (DFT) calcns. The oxidative addn. of a C-H bond of partially fluorinated benzenes, C6FnH6-n (n = 0-5) to a Ni(0) phosphine complex is reversible, but the oxidative addn. of a C-F bond yields a stable product via a high-energy barrier. A pathway via the Ni(II) hydride complex is eliminated on the basis of a calcd. H/D kinetic isotope effect (KIE) that does not agree with the measured value. An alternate pathway was detd., using as reactant a Ni(phosphine)(alkyne) complex that is shown to be the major species in the reactive media under the catalytic conditions. This pathway is initiated by arene coordination to the Ni alkyne complex followed by proton transfer from the σ-C-H bond of the coordinated arene to the alkyne as the C-H activation step. Anal. of the charge distribution shows that the alkyne is strongly neg. charged when coordinated to the Ni(phosphine) species, which favors a C-H activation as a proton transfer, similar to that in CMD and AMLA but not previously seen between hydrocarbyl ligands for electron rich metals. The C-H activation step thus represents an example of a general class of mechanism that we term ligand-to-ligand hydrogen transfer (LLHT). The product of this reaction is a nickel(vinyl)(aryl) complex, which rearranges to place the aryl and vinyl groups cis to one another before undergoing reductive elimination of the arylalkene. An anal. of the calcd. turnover frequencies shows that the rate-detg. states that control the energy span are the alkyne complex + free arene and the transition state for the vinyl-aryl complex trans-to-cis rearrangement. The calcd. KIE agrees with the obsd. lack of isotope effect. Anal. of the effects of fluorine substituents shows that the Ni-C(aryl) bond energies control the energy barriers for the arene C-H activation step and the energy spans. A correlation between bond dissocn. energies for the Ni-C(aryl) bond and the arene C-H bond follows the behavior presented previously, in which the effects of ortho fluorine substituents are dominant. Consequently, fluorine substitution of the arene, esp. at the ortho positions, strengthens the Ni-C bond and increases the TOF. The LLHT mechanism described here may also apply to nickel-catalyzed C-H activation reactions with other substrates.
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  .
  (b) Tang, S.; Eisenstein, O.; Nakao, Y.; Sakaki, S. Aromatic C–H σ-Bond Activation by Ni0, Pd0, and Pt0 Alkene Complexes: Concerted Oxidative Addition to Metal vs Ligand-to-Ligand H Transfer Mechanism. Organometallics 2017, 36, 2761– 2771, DOI: 10.1021/acs.organomet.7b00256
  [ ACS Full Text ], [ CAS], Google Scholar
  8b
  Aromatic C-H σ-Bond Activation by Ni0, Pd0, and Pt0 Alkene Complexes: Concerted Oxidative Addition to Metal vs Ligand-to-Ligand H Transfer Mechanism
  Tang, Shuwei; Eisenstein, Odile; Nakao, Yoshiaki; Sakaki, Shigeyoshi
  Organometallics (2017), 36 (15), 2761-2771CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  C-H σ-bond activation of arene (represented here by benzene) by the Ni0 propene complex Ni0(IMes)(C3H6) (IMes = 1,3-dimesitylimidazol-2-ylidene), which is an important elementary step in Ni-catalyzed hydroarylation of unactivated alkene with arene, was investigated by DFT calcns. In the Ni0 complex, the C-H activation occurs through a ligand-to-ligand H transfer mechanism to yield NiII(IMes)(C3H7)(Ph) (C3H7 = propyl; Ph = phenyl). In Pd0 and Pt0 analogs, the activation occurs through concerted oxidative addn. of the C-H bond to the metal. Anal. of the electron redistribution during the C-H activation highlights the difference between the two mechanisms. In the ligand-to-ligand H transfer, charge transfer (CT) occurs from the metal to the benzene. However, the at. population of the transferring H remains almost const., suggesting that different CT simultaneously occurs from the transferring H to the LUMO of propene. The electron redistribution contrasts significantly with that found for Pd0 and Pt0, in which CT occurs only from the metal to the benzene. Preference for ligand-to-ligand H transfer over concerted oxidative addn. in the Ni0 complex is shown to be due to the smaller at. radius of Ni in comparison to those of Pd and Pt and the smaller NiII-H bond energy relative to the PdII-H and PtII-H energies. Interestingly, the bulky ligand accelerates the ligand-to-ligand H transfer in the Ni0 complex by decreasing the distance between the coordinated benzene and alkene substrates. Thus, the Gibbs activation energy (ΔG°⧺) decreases in the case of cyclic-alkylaminocarbene with bulky substituents (CACC-K3), while the ΔG°⧺ values are similar in X-Phos, IMes, and nonsubstituted cyclic alkylaminocarbene (CAAC-K0). An electron-withdrawing substituent on the arene accelerates the C-H activation by favoring the metal to arene CT.
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  .
  (c) Yamazaki, K.; Obata, A.; Sasagawa, A.; Ano, Y.; Chatani, N. Computational Mechanistic Study on the Nickel-Catalyzed C–H/N–H Oxidative Annulation of Aromatic Amides with Alkynes: The Role of the Nickel (0) Ate Complex. Organometallics 2019, 38, 248– 255, DOI: 10.1021/acs.organomet.8b00684
  [ ACS Full Text ], [ CAS], Google Scholar
  8c
  Computational Mechanistic Study on the Nickel-Catalyzed C-H/N-H Oxidative Annulation of Aromatic Amides with Alkynes: The Role of the Nickel(0) Ate Complex
  Yamazaki, Ken; Obata, Atsushi; Sasagawa, Akane; Ano, Yusuke; Chatani, Naoto
  Organometallics (2019), 38 (2), 248-255CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  D. functional theory (DFT) was used to unveil intimate mechanistic insights on the monodentate-chelation system that is used in the Ni-catalyzed C-H/N-H oxidative annulation of arom. amides with alkynes, a reaction that was originally reported by our group (Chem Sci. 2017, 8, 6650-6655, DOI: 10.1039/C7SC01750B). The proposed reaction mechanism involves two reaction paths. The initial path is initiated by Ni(II), and the other, the main catalytic cycle, is initiated by Ni(0). Both paths require the presence of a catalytic amt. of KOBut. The results of the DFT studies presented here indicate that the rate-detg. step in the initial Ni(II) system involves a concerted metalation-deprotonation (CMD) mechanism and an anionic Ni(0) ate complex is the key intermediate in the main catalytic cycle. Furthermore, a previously proposed oxidative addn.-alkyne insertion sequence is revised to a ligand-to-ligand hydrogen transfer (LLHT) mechanism, which is the rate-detg. step in the main catalytic cycle. The computed regioselectivity of the asym. alkynes and meta-substituted arom. amides that are produced in such reactions is in good agreement with the exptl. results.
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9. 9
  (a) Shibata, K.; Hasegawa, N.; Fukumoto, Y.; Chatani, N. Ruthenium-Catalyzed Carbonylation of ortho C–H Bonds in Arylacetamides: C–H Bond Activation Utilizing a Bidentate-Chelation System. ChemCatChem 2012, 4, 1733– 1736, DOI: 10.1002/cctc.201200352
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  9a
  Ruthenium-Catalyzed Carbonylation of ortho C-H Bonds in Arylacetamides: C-H Bond Activation Utilizing a Bidentate-Chelation System
  Shibata, Kaname; Hasegawa, Nao; Fukumoto, Yoshiya; Chatani, Naoto
  ChemCatChem (2012), 4 (11), 1733-1736CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The Ru-catalyzed C-H bond carbonylation of arylacetamides with a 2-pyridinylmethylamine moiety as the bidentate directing group is reported. The reaction involves the regioselective activation of C(sp2)-H bonds at the ortho C-H position. Coordination in an N,N'-fashion is a key step in this reaction. E.g., in presence of Ru3(CO)12 and ethylene in toluene/H2O, carbonylation of amide (I) gave 93% isoquinolinedione deriv. (II).
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  .
  (b) Hasegawa, N.; Shibata, K.; Charra, V.; Inoue, S.; Fukumoto, Y.; Chatani, N. Ruthenium-catalyzed cyclocarbonylation of aliphatic amides through the regioselective activation of unactivated C(sp3)–H bonds. Tetrahedron 2013, 69, 4466– 4472, DOI: 10.1016/j.tet.2013.02.006
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  9b
  Ruthenium-catalyzed cyclocarbonylation of aliphatic amides through the regioselective activation of unactivated C(sp3)-H bonds
  Hasegawa, Nao; Shibata, Kaname; Charra, Valentine; Inoue, Satoshi; Fukumoto, Yoshiya; Chatani, Naoto
  Tetrahedron (2013), 69 (22), 4466-4472CODEN: TETRAB; ISSN:0040-4020. (Elsevier Ltd.)
  The regioselective carbonylation of unactivated C(sp3)-H bonds of aliph. amides, using 2-pyridinylmethylamine as a directing group in conjunction with Ru3(CO)12 as a catalyst is described. The presence of a 2-pyridinylmethylamine moiety in the amides is crucial for the success of the reaction. Although ethylene is not incorporated into the products, its presence is also essential for the reaction to proceed. Furthermore, the addn. of H2O is important for the reaction to proceed efficiently. The reaction shows a high preference for the C-H bonds of Me groups, compared to methylene C-H bonds, even the methylene C-H bonds are activated by the presence of an oxygen atom or an aryl group. In addn., the reaction tolerates various functional groups, such as MeO, Cl, CF3, CN, and even Br substituents. The reaction of α-mono-substituted aliph. amides gave the corresponding carbonylation products in lower yields, although the use of α,α-di-substituted aliph. amides resulted in high product yields. The use of a sterically demanding directing group, such as 1-(2-pyridinylethyl)amine moiety, in α-mono-substituted aliph. amides improved the yields of the products. The stoichiometric reaction of an amide with Ru3(CO)12 gave a stable di-nuclear ruthenium complex as a single ruthenium complex in which the 2-pyridinylmethylamino moiety is coordinated to the ruthenium center in a N,N-manner and an amide carbonyl oxygen binds to the other ruthenium center, but C-H bond activation is not involved. The complex itself does not show catalytic activity, but is activated in the presence of H2O under the catalytic reaction conditions employed.
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  .
  (c) Misal Castro, L. C.; Obata, A.; Aihara, Y.; Chatani, N. Chelation-Assisted Nickel-Catalyzed Oxidative Annulation via Double C–H Activation/Alkyne Insertion Reaction. Chem. Eur. J. 2016, 22, 1362– 1367, DOI: 10.1002/chem.201504596
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  9c
  Chelation-Assisted Nickel-Catalyzed Oxidative Annulation via Double C-H Activation/Alkyne Insertion Reaction
  Misal Castro, Luis C.; Obata, Atsushi; Aihara, Yoshinori; Chatani, Naoto
  Chemistry - A European Journal (2016), 22 (4), 1362-1367CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A nickel/NHC system for regioselective oxidative annulation by double carbon-hydrogen bond (C-H bond) activation and concomitant alkyne insertion is described. The catalytic reaction requires a bidentate directing group, such as an 8-aminoquinoline, embedded in the substrate. Various 5,6,7,8-tetrasubstituted-N-(8-quinolinyl)-1-naphthamides can be prepd. as well as phenanthrene and benzo[h]quinoline amide derivs. Diarylalkynes, dialkylalkynes, and (aryl)alkynes can be used in the system. A Ni0/NiII catalytic cycle is proposed as the main catalytic cycle. The alkyne plays a double role as a two-component coupling partner and as a hydrogen acceptor. Under optimized conditions the synthesis of the target compds. was achieved using dibromo[1,2-di(methoxy-κO)ethane]nickel [i.e., Ni(dme)Br2, dibromo(glyme)nickel] and 1,3-bis(2,4,6-trimethylphenyl)-1H-imidazolium bromide (i.e., IMes) and 4,5-dihydro-1,3-bis(2,4,6-trimethylphenyl)-1H-imidazolium chloride (i.e., SIMes) as catalyst and ligand combination. Starting materials included alkynes, sych as 1,1'-(1,2-ethynediyl)bis[benzene], 8-hexadecyne, (1-propynyl)benzene, (1-butynyl)ebnzene, (1-hexynyl)benzene, 2-(1-propynyl)thiophene and amides, such as N-(8-quinolinyl)benzamide derivs., 9-methyl-N-(8-quinolinyl)-9H-carbazole-3-carboxamide. The title compds. thus formed included N-(8-quinolinyl)-1-naphthalenecarboxamide derivs.
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  (d) He, Z.; Huang, Y. Diverting C–H Annulation Pathways: Nickel-Catalyzed Dehydrogenative Homologation of Aromatic Amides. ACS Catal. 2016, 6, 7814– 7823, DOI: 10.1021/acscatal.6b02477
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  9d
  Diverting C-H Annulation Pathways: Nickel-Catalyzed Dehydrogenative Homologation of Aromatic Amides
  He, Zhiqi; Huang, Yong
  ACS Catalysis (2016), 6 (11), 7814-7823CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Direct homologation of arom. amides with internal alkynes has been accomplished via a nickel-catalyzed sequential C-H activation reaction. The use of a rigid chelating group and a strong aprotic polar solvent successfully divert the classical [4+2] annulation to the [2+2+2] homologation pathway. This transformation is promoted by a simple nickel catalyst without the need of stoichiometric metal oxidants. Mechanistic studies support an unusual substrate-assisted ligand exchange process. NMR and X-ray data suggest a [5,5] Ni-bridged metallacycle as the catalyst resting state. Substrate assisted directing group swap plays an important role for the subsequent meta-C-H insertion. In contrast, [4 + 2] annulation can be accomplished using a bulky, electron-rich phosphine ligand, which favors rapid reductive C-N elimination.
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10. 10
  For computational studies of Ni-catalyzed C–H functionalization using N,N-bidentate strategy, see:
  (a) Tang, H.; Zhou, B.; Huang, X.-R.; Wang, C.; Yao, J.; Chen, H. Origins of Selective C(sp2)–H Activation Using Transition Metal Complexes with N,N-Bidentate Directing Groups: A Combined Theoretical–Experimental Study. ACS Catal. 2014, 4, 649– 656, DOI: 10.1021/cs401141k
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  10a
  Origins of Selective C(sp2)-H Activation Using Transition Metal Complexes with N,N-Bidentate Directing Groups: A Combined Theoretical-Experimental Study
  Tang, Hao; Zhou, Bingwei; Huang, Xu-Ri; Wang, Congyang; Yao, Jiannian; Chen, Hui
  ACS Catalysis (2014), 4 (2), 649-656CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  The strategy using N,N-bidentate directing groups is a promising way to achieve selective C-(sp2)-H activation inaccessible by that of monodentate directing groups. Herein, through theor. calcns., the authors present a rationale behind this strategy, which deciphers its key roles in C-H activation promoted by Ni, Pd, Ru, and Cu. The calcns. reveal two key points: (a) Between the two coordination sites of the N,N-bidentate directing group, the proximal one influences more the C-H activation barrier ΔG‡, whereas the distal site affects more the free energy change ΔG relevant to the substrate coordination. (b) Enlarging/shrinking the chelation ring can exert different effects on the reactivity, depending on the metal identity and the ring size. Importantly, the authors' computational results are in full agreement with previous exptl. findings concerning reactivity. Also, a prediction about the unprecedented reactivity from the authors' theory is confirmed by the authors' expts., lending more credence to the rationale and insights gained.
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  .
  (b) Tang, H.; Huang, X.-R.; Yao, J.; Chen, H. Understanding the Effects of Bidentate Directing Groups: A Unified Rationale for sp2 and sp3 C–H Bond Activations. J. Org. Chem. 2015, 80, 4672– 4682, DOI: 10.1021/acs.joc.5b00580
  [ ACS Full Text ], [ CAS], Google Scholar
  10b
  Understanding the Effects of Bidentate Directing Groups: A Unified Rationale for sp2 and sp3 C-H Bond Activations
  Tang, Hao; Huang, Xu-Ri; Yao, Jiannian; Chen, Hui
  Journal of Organic Chemistry (2015), 80 (9), 4672-4682CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  Bidentate directing group (DG) strategy is a promising way to achieve sp2 and more inert sp3 C-H bond activations in transition metal (TM) catalysis. In this work, we systematically explored the assisting effects exerted by bidentate DGs in the C-H bond activations. Through DFT calcns. and well-defined comparative anal., we for the first time unified the rationale of the reactivity promoted by bidentate DG in sp2 and sp3 C-H activations, which are generally consistent with available exptl. discoveries about the C-H activation reactivity up to date. In addn. to the general rationale of the reactivity, the assisting effects of several typical bidentate DGs were also quant. evaluated and compared to reveal their relative promoting ability for C-H activation reactivity. Finally, the effect of the ligating group charge and the position of the ligating group charge in bidentate DGs were also investigated, based on which new types of DGs were designed and proposed to be potentially effective in C-H activation. The deeper understanding and new insight about the bidentate DG strategy gained in this work would help to enhance its further exptl. development in sp2 and sp3 C-H bond activations.
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  .
  (c) Xu, Z.-Y.; Jiang, Y.-Y.; Yu, H.-Z.; Fu, Y. Mechanism of Nickel(II)-Catalyzed Oxidative C(sp2)–H/C(sp3)–H Coupling of Benzamides and Toluene Derivatives. Chem. - Asian J. 2015, 10, 2479– 2483, DOI: 10.1002/asia.201500599
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  10c
  Mechanism of Nickel(II)-Catalyzed Oxidative C(sp2)-H/C(sp3)-H Coupling of Benzamides and Toluene Derivatives
  Xu, Zheng-Yang; Jiang, Yuan-Ye; Yu, Hai-Zhu; Fu, Yao
  Chemistry - An Asian Journal (2015), 10 (11), 2479-2483CODEN: CAAJBI; ISSN:1861-4728. (Wiley-VCH Verlag GmbH & Co. KGaA)
  The Ni-catalyzed C(sp2)-H/C(sp3)-H coupling of benzamides with toluene derivs. was recently successfully achieved with mild oxidant iC3F7I. Herein, we employ d. functional theory (DFT) methods to resolve the mechanistic controversies. Two previously proposed mechanisms are excluded, and our proposed mechanism involving iodine-atom transfer (IAT) between iC3F7I and the NiII intermediate was found to be more feasible. With this mechanism, the presence of a carbon radical is consistent with the exptl. observation that (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) completely quenches the reaction. Meanwhile, the hydrogen-atom abstraction of toluene is irreversible and the activation of the C(sp2)-H bond of benzamides is reversible. Both of these conclusions are in good agreement with Chatanis deuterium-labeling expts.
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  (d) Singh, S.; K, S.; Sunoj, R. B. Aliphatic C(sp3)–H Bond Activation Using Nickel Catalysis: Mechanistic Insights on Regioselective Arylation. J. Org. Chem. 2017, 82, 9619– 9626, DOI: 10.1021/acs.joc.7b01672
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  10d
  Aliphatic C(sp3)-H Bond Activation Using Nickel Catalysis: Mechanistic Insights on Regioselective Arylation
  Singh, Sukriti; K, Surya; Sunoj, Raghavan B.
  Journal of Organic Chemistry (2017), 82 (18), 9619-9626CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  Transition-metal-catalyzed C(sp3)-H bond activation in aliph. compds. are of current interest. Lack of mechanistic insights on Ni-catalyzed C(sp3)-H activation using 8-aminoquinoline as a directing group motivated us to examine an interesting direct arylation of an aliph. tertiary amide by using d. functional theory. The catalysis employed Ni(II) precatalyst, 4-iodoanisole as an arylating agent, sodium carbonate, and mesitylenic acid as additives in DMF solvent. Examn. of a comprehensive set of mechanistic pathways helped us learn that the most preferred route begins with a bidentate chelate binding of deprotonated substrate to the Ni. The C-H activation in the catalyst-substrate complex via a cyclometalation deprotonation provides a five-membered nickelacycle intermediate, which upon the rate-limiting oxidative insertion to aryl iodide forms a Ni(IV)-aryl intermediate. The ensuing reductive elimination furnishes the desired arylated product. We note that the explicit inclusion of sodium carbonate, mesitylenic acid, and solvent mols. on sodium ion all are crit. in identifying the most favorable pathway. Of the two types of C(sp3)-H bonds in the substrate [2-methyl-2-phenyl-N-(quinolin-8-yl)heptanamide], the energies for the regio-controlling reductive elimination is predicted to be more in favor of the Me group than the methylene of the pentyl chain, in excellent agreement with the previous exptl. observation.
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  (e) Omer, H. M.; Liu, P. Computational Study of Ni-Catalyzed C–H Functionalization: Factors That Control the Competition of Oxidative Addition and Radical Pathways. J. Am. Chem. Soc. 2017, 139, 9909– 9920, DOI: 10.1021/jacs.7b03548
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  10e
  Computational Study of Ni-Catalyzed C-H Functionalization: Factors That Control the Competition of Oxidative Addition and Radical Pathways
  Omer, Humair M.; Liu, Peng
  Journal of the American Chemical Society (2017), 139 (29), 9909-9920CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The mechanisms of Ni-catalyzed C-H arylation, alkylation, and sulfenylation with N,N-bidentate directing groups are investigated using d. functional theory (DFT) calcns. While the C-H cleavage occurs via the concerted metalation-deprotonation (CMD) mechanism in all types of reactions, the subsequent C-C and C-X bond formation steps may occur via either oxidative addn. to form a Ni(IV) intermediate or radical pathways involving Ni(III) complexes generated from homolytic dissocn. of disulfides/peroxides or halide-atom transfer from alkyl halides. DFT calcns. revealed that radical mechanisms are preferred in reactions with sterically hindered coupling partners with relatively low bond dissocn. energies (BDE) such as dicumyl peroxide, heptafluoroisopropyl iodide and di-Ph disulfide. In contrast, these radical processes are highly disfavored when generating unstable Ph and primary alkyl radicals. In such cases, the reaction proceeds via an oxidative addn./reductive elimination mechanism involving a Ni(IV) intermediate. These theor. insights into the substrate-controlled mechanisms in the C-H functionalizations were employed to investigate a no. of exptl. phenomena including substituent effects on reactivity, chemo- and regioselectivity and the effects of oxidant in the intermol. oxidative C-H/C-H coupling reactions.
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  (f) Haines, B. E.; Yu, J.-Q.; Musaev, D. G. The mechanism of directed Ni(II)-catalyzed C–H iodination with molecular iodine. Chem. Sci. 2018, 9, 1144– 1154, DOI: 10.1039/C7SC04604A
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  10f
  The mechanism of directed Ni(II)-catalyzed C-H iodination with molecular iodine
  Haines, Brandon E.; Yu, Jin-Quan; Musaev, Djamaladdin G.
  Chemical Science (2018), 9 (5), 1144-1154CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  The d. functional theory method is used to elucidate the elementary steps of Ni(II)-catalyzed C(sp2)-H iodination with I2 and substrates bearing N,N'-bidentate directing centers, amide-oxazoline (AO) and 8-aminoquinoline (AQ). The relative stability of the lowest energy high- and low-spin electronic states of the catalyst and intermediates is found to be an important factor for all of the steps in the reaction. As a result, two-state reactivity for these systems is reported, where the reaction is initiated on the triplet surface and generates a high energy singlet nickelacycle. It is shown that the addn. of Na2CO3 base to the reaction mixt. facilitates C-H activation. The presence of I2 in the reaction provides the much needed driving force for the C-H activation and nickelacycle formation and ultimately reacts to form a new C-I bond through either a redox neutral electrophilic cleavage (EC) pathway or a one-electron reductive cleavage (REC) pathway. The previously proposed Ni(II)/Ni(IV) and homolytic cleavage pathways are found to be higher in energy. The nature of the substrate is found to have a large impact on the relative stability of the lowest electronic states and on the stability of the nickelacycle resulting from C-H activation.
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  (g) Li, Y.; Zou, L.; Bai, R.; Lan, Y. Ni(I)–Ni(III) vs. Ni(II)–Ni(IV): mechanistic study of Ni-catalyzed alkylation of benzamides with alkyl halides. Org. Chem. Front. 2018, 5, 615– 622, DOI: 10.1039/C7QO00850C
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  10g
  Ni(I)-Ni(III) vs. Ni(II)-Ni(IV): mechanistic study of Ni-catalyzed alkylation of benzamides with alkyl halides
  Li, Yingzi; Zou, Lufeng; Bai, Ruopeng; Lan, Yu
  Organic Chemistry Frontiers (2018), 5 (4), 615-622CODEN: OCFRA8; ISSN:2052-4129. (Royal Society of Chemistry)
  Nickel-catalyzed C-H bond activation has attracted significant attention for the construction of C-C bond frameworks. We report d. functional theory investigations into the mechanism of nickel-catalyzed alkylation of benzamides with alkyl halides. Both the Ni(I)-Ni(III) and Ni(II)-Ni(IV) catalytic cycles were considered. The theor. study indicated that the most feasible mechanism involved a Ni(II)-Ni(IV) catalytic cycle with four main steps: (i) N-H bond activation and (ii) C-H bond activation through the concerted metalation-deprotonation pathway, (iii) oxidative addn. of BuBr to give a high-valent Ni(IV) complex, and (iv) C-C reductive elimination to generate the product and the active catalyst. The rate-detg. step of the favored pathway is the oxidative addn., leading to the generation of a Ni(IV) intermediate. In addn., the present study casts light on the role of PPh3, which accelerates the cleavage of N-H bond. Frontier MO theory and natural population anal. were employed to explain the effect of the phosphine ligand on the structure of the Ni complex.
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11. 11
  For computational studies of other metal-catalyzed C–H functionalization using N,N-bidentate group strategy, see:
  (a) Cross, W. B.; Hope, E. G.; Lin, Y.-H.; Macgregor, S. A.; Singh, K.; Solan, G. A.; Yahyaa, N. N,N-Chelate-control on the regioselectivity in acetate-assisted C–H activation. Chem. Commun. 2013, 49, 1918– 1920, DOI: 10.1039/c3cc38697j
  [ Crossref], [ PubMed], [ CAS], Google Scholar
  11a
  N,N-Chelate-control on the regioselectivity in acetate-assisted C-H activation
  Cross, Warren B.; Hope, Eric G.; Lin, Yi-Hsien; Macgregor, Stuart A.; Singh, Kuldip; Solan, Gregory A.; Yahya, Nurhusna
  Chemical Communications (Cambridge, United Kingdom) (2013), 49 (19), 1918-1920CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Preferential peri- vs. more common ortho-cyclopalladation was achieved in reaction of 1-[6-(iminoethyl)-2-pyridyl]naphthalene with palladium acetate, producing tridentate C,N,N-ligated pincer complex; 6-aminoethyl- analog also metalates in peri-position, whereas 6-hydroxyethyl undergoes ortho-palladation with formation of C2,N,O-pincer. Bidentate N,N-pyridylimine or N,N-pyridylamine donors are effective chelating ligands for regiospecific C-H activation at the peri-(C8)-position of a naphthyl ring on reaction with palladium(ii) acetate; DFT calcns. show N,N-chelates bias the cyclopalladation towards 6-membered ring products.
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  .
  (b) Huang, L.; Li, Q.; Wang, C.; Qi, C. Palladium(II)-Catalyzed Regioselective Arylation of Naphthylamides with Aryl Iodides Utilizing a Quinolinamide Bidentate System. J. Org. Chem. 2013, 78, 3030– 3038, DOI: 10.1021/jo400017v
  [ ACS Full Text ], [ CAS], Google Scholar
  11b
  Palladium(II)-Catalyzed Regioselective Arylation of Naphthylamides with Aryl Iodides Utilizing a Quinolinamide Bidentate System
  Huang, Lehao; Li, Qian; Wang, Chen; Qi, Chenze
  Journal of Organic Chemistry (2013), 78 (7), 3030-3038CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  A palladium(II)-catalyzed quinolinamide-directed 8-arylation of 1-naphthylamides with aryl iodides is reported. The bidentate directing group (quinolinamide) proved to be crucial for a highly regioselective transformation. E.g., in presence of Pd(OAc)2 and KOAc in xylene, arylation of N-(1-naphthyl)quinoline-2-carboxamide (I) with 4-iodotoluene gave 85% II. In addn., the amide directing group can be easily hydrolyzed under basic conditions to offer a range of 8-aryl-1-naphthylamine derivs. The theor. calcns. suggest that the C-H arylation reaction proceeds through a sequential C-H activation/oxidative addn. pathway.
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  .
  (c) Wei, Y.; Tang, H.; Cong, X.; Rao, B.; Wu, C.; Zeng, X. Pd(II)-Catalyzed Intermolecular Arylation of Unactivated C(sp3)–H Bonds with Aryl Bromides Enabled by 8-Aminoquinoline Auxiliary. Org. Lett. 2014, 16, 2248– 2251, DOI: 10.1021/ol500745t
  [ ACS Full Text ], [ CAS], Google Scholar
  11c
  Pd(II)-Catalyzed Intermolecular Arylation of Unactivated C(sp3)-H Bonds with Aryl Bromides Enabled by 8-Aminoquinoline Auxiliary
  Wei, Yu; Tang, Huarong; Cong, Xuefeng; Rao, Bin; Wu, Chao; Zeng, Xiaoming
  Organic Letters (2014), 16 (8), 2248-2251CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
  An example of using readily available, less reactive aryl bromides as arylating reagents in the Pd(II)-catalyzed intermol. arylation of unactivated C(sp3)-H bonds is described. This reaction was promoted by a crucial 8-aminoquinolinyl directing group and a K2CO3 base, enabling regiospecific installation of an aryl scaffold at the β-position of carboxamides. A mechanistic study by DFT calcns. reveals a C(sp3)-H activation-led pathway featuring the oxidative addn. as the highest energy transition state.
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  .
  (d) Shan, C.; Luo, X.; Qi, X.; Liu, S.; Li, Y.; Lan, Y. Mechanism of Ruthenium-Catalyzed Direct Arylation of C–H Bonds in Aromatic Amides: A Computational Study. Organometallics 2016, 35, 1440– 1445, DOI: 10.1021/acs.organomet.6b00064
  [ ACS Full Text ], [ CAS], Google Scholar
  11d
  Mechanism of Ruthenium-Catalyzed Direct Arylation of C-H Bonds in Aromatic Amides: A Computational Study
  Shan, Chunhui; Luo, Xiaoling; Qi, Xiaotian; Liu, Song; Li, Yingzi; Lan, Yu
  Organometallics (2016), 35 (10), 1440-1445CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Ruthenium-catalyzed arylation of ortho C-H bonds directed by a bidentate 8-aminoquinoline moiety not only is important to construct new biaryl derivates but also merges important research areas. In this study, the d. functional theory (DFT) method M11-L was employed to predict the mechanism of this C-H bond arylation reaction. The computational results indicate that the initial step for this reaction is catalyst loading by electrophilic deprotonation to generate a substrate-coordinated Ru(II) intermediate, which is the key compd. in the complete catalytic cycle. The catalytic cycle includes electrophilic deprotonation by carbonate, oxidative addn. of bromobenzene, reductive elimination to form a new aryl-aryl bond, proton transfer to release the product, and ligand exchange to regenerate the initial Ru(II) intermediate. Theor. calcns. suggest that the oxidative addn. of bromobenzene is the rate-detg. step of the whole catalytic cycle, and the apparent activation free energy is 32.7 kcal/mol. The ligand effect was considered in DFT calcns., and the calcd. results agree well with exptl. observations.
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  .
  (e) Chen, C.; Hao, Y.; Zhang, T.-Y.; Pan, J.-L.; Ding, J.; Xiang, H.-Y.; Wang, M.; Ding, T.-M.; Duan, A.; Zhang, S.-Y. Computational and experimental studies on copper-mediated selective cascade C–H/N–H annulation of electron-deficient acrylamide with arynes. Chem. Commun. 2019, 55, 755– 758, DOI: 10.1039/C8CC08708C
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  11e
  Computational and experimental studies on copper-mediated selective cascade C-H/N-H annulation of electron-deficient acrylamide with arynes
  Chen, Chao; Hao, Yu; Zhang, Ting-Yu; Pan, Jin-Long; Ding, Jun; Xiang, Heng-Ye; Wang, Man; Ding, Tong-Mei; Duan, Abing; Zhang, Shu-Yu
  Chemical Communications (Cambridge, United Kingdom) (2019), 55 (6), 755-758CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  An efficient and convenient copper-mediated method has been developed to achieve direct cascade C-H/N-H annulation for the synthesis of 2-quinolinones e.g., I from electron-deficient acrylamides e.g., II and arynes e.g., 4,5-dimethyl-2-(trimethylsilyl)phenyl trifluoromethanesulfonate. This method highlights an emerging but simple strategy to transform inert C-H bonds into versatile functional groups in org. synthesis to provide a new method of synthesizing 2-quinolinones efficiently. Mechanistic investigation by exptl. and d. functional theory (DFT) studies suggest that an organometallic C-H activation via a Cu(III) intermediate is likely to be involved in the reaction.
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  .
  (f) Dewyer, A. L.; Zimmerman, P. M. Simulated Mechanism for Palladium Catalyzed, Directed γ-Arylation of Piperidine. ACS Catal. 2017, 7, 5466– 5477, DOI: 10.1021/acscatal.7b01390
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  11f
  Simulated Mechanism for Palladium-Catalyzed, Directed γ-Arylation of Piperidine
  Dewyer, Amanda L.; Zimmerman, Paul M.
  ACS Catalysis (2017), 7 (8), 5466-5477CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Quantum chem. reaction path finding methods are herein used to investigate the mechanism of Pd-catalyzed distal functionalization of piperidine, as reported by Sanford. These methods allowed navigation of a complex reaction landscape with multiple reactants interacting at all key steps of the proposed catalytic cycle. A multistep cycle is shown to conceptually begin with substrate ligation and Pd(II)-catalyzed C-H activation, which occurs through concerted metalation-deprotonation. In subsequent steps, the kinetic and thermodn. profiles for oxidative addn., reductive elimination, and catalyst regeneration show why excess Cs salts and ArI were required in the expt. Specifically, excess ArI is necessary to thermodynamically overcome the high energy of the C-H activated intermediate and allow oxidative addn. to be favorable, and excess Cs salt is needed to sequester reaction byproducts during oxidative addn. and catalyst regeneration. The overall catalytic profile is consistent with rate-limiting C-H activation, explains the probable functions of all major exptl. conditions, and gives atomistic detail to guide expt. to improve this challenging transformation even further.
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12. 12
  Shiota, H.; Ano, Y.; Aihara, Y.; Fukumoto, Y.; Chatani, N. Nickel-Catalyzed Chelation-Assisted Transformations Involving Ortho C–H Bond Activation: Regioselective Oxidative Cycloaddition of Aromatic Amides to Alkynes. J. Am. Chem. Soc. 2011, 133, 14952– 14955, DOI: 10.1021/ja206850s
  [ ACS Full Text ], [ CAS], Google Scholar
  12
  Nickel-catalyzed chelation-assisted transformations involving ortho C-H bond activation: regioselective oxidative cycloaddition of aromatic amides to alkynes
  Shiota, Hirotaka; Ano, Yusuke; Aihara, Yoshinori; Fukumoto, Yoshiya; Chatani, Naoto
  Journal of the American Chemical Society (2011), 133 (38), 14952-14955CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Although the pioneering example of ortho metalation involving cleavage of C-H bonds was achieved using a nickel complex, no examples of catalysis using nickel complexes have been reported. In this work, the Ni-catalyzed transformation of ortho C-H bonds utilizing chelation assistance, such as oxidative cycloaddn. of arom. amides with alkynes, has been achieved.
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13. 13
  For a recent computational study on this reaction, see:Zhang, X.; Zhao, Q.; Fan, J.-Q.; Chen, D.-Z.; Liu, J.-B. A computational mechanistic study of Ni(0)-catalyzed annulation of aromatic amides with alkynes: the effects of directing groups. Org. Chem. Front. 2019, DOI: 10.1039/C8QO01310A
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  There is no corresponding record for this reference.
14. 14
  For select examples of chelation-assisted Ni-catalyzed C–H arylation, see:
  (a) Aihara, Y.; Chatani, N. Nickel-Catalyzed Direct Arylation of C(sp3)–H Bonds in Aliphatic Amides via Bidentate-Chelation Assistance. J. Am. Chem. Soc. 2014, 136, 898– 901, DOI: 10.1021/ja411715v
  [ ACS Full Text ], [ CAS], Google Scholar
  14a
  Nickel-Catalyzed Direct Arylation of C(sp3)-H Bonds in Aliphatic Amides via Bidentate-Chelation Assistance
  Aihara, Yoshinori; Chatani, Naoto
  Journal of the American Chemical Society (2014), 136 (3), 898-901CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The Ni-catalyzed, direct arylation of C-(sp3)-H (Me and methylene) bonds in aliph. amides contg. an 8-aminoquinoline moiety as a bidentate directing group with aryl halides is described. Deuterium-labeling expts. indicate that the C-H bond cleavage step is fast and reversible. Various nickel complexes including both Ni-(II) and Ni(0) show a high catalytic activity. The results of a series of mechanistic expts. indicate that the catalytic reaction does not proceed through a Ni(0)/Ni-(II) catalytic cycle, but probably through a Ni-(II)/Ni-(IV) catalytic cycle.
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  .
  (b) Yokota, A.; Aihara, Y.; Chatani, N. Nickel(II)-Catalyzed Direct Arylation of C–H Bonds in Aromatic Amides Containing an 8-Aminoquinoline Moiety as a Directing Group. J. Org. Chem. 2014, 79, 11922– 11932, DOI: 10.1021/jo501697n
  [ ACS Full Text ], [ CAS], Google Scholar
  14b
  Nickel(II)-Catalyzed Direct Arylation of C-H Bonds in Aromatic Amides Containing an 8-Aminoquinoline Moiety as a Directing Group
  Yokota, Ayana; Aihara, Yoshinori; Chatani, Naoto
  Journal of Organic Chemistry (2014), 79 (24), 11922-11932CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  Arylation via the cleavage of the ortho C-H bonds by a nickel-catalyzed reaction of arom. amides contg. an 8-aminoquinoline moiety with aryl iodides is reported. The reaction shows a high functional group compatibility. The reaction proceeds in a highly selective manner at the less hindered C-H bonds in the reaction of meta-substituted arom. amides, irresp. of the electronic nature of the substituents. Electron-withdrawing groups on the arom. amides facilitate the reaction. Various mechanistic expts., such as deuterium labeling expts., Hammett studies, competition expts., and radical trap expts., were made for better understanding the reaction mechanism. The cleavage of C-H bonds is reversible from the deuterium labeling expts. Both Ni(II) and Ni(0) show a high catalytic activity, but the results of mechanistic expts. suggest that a Ni(0)/Ni(II) catalytic cycle is not involved.
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  .
  (c) Li, M.; Dong, J.; Huang, X.; Li, K.; Wu, Q.; Song, F.; You, J. Nickel-catalyzed chelation-assisted direct arylation of unactivated C(sp3)–H bonds with aryl halides. Chem. Commun. 2014, 50, 3944– 3946, DOI: 10.1039/C4CC00716F
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  14c
  Nickel-catalyzed chelation-assisted direct arylation of unactivated C(sp3)-H bonds with aryl halides
  Li, Mingliang; Dong, Jiaxing; Huang, Xiaolei; Li, Kaizhi; Wu, Qian; Song, Feijie; You, Jingsong
  Chemical Communications (Cambridge, United Kingdom) (2014), 50 (30), 3944-3946CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  In this work, we have disclosed the nickel-catalyzed unactivated β-C(sp3)-H bond arylation of aliph. acid derivs. with aryl iodides/bromides via bidentate chelation-assistance of an 8-aminoquinoline moiety. E.g., in presence of a Ni catalyst, arylation of 8-quinolinyl-substituted amide I with 4-IC6H4OMe gave 83% II. The best results were obtained by using Ni(OTf)2 as the catalyst, PPh3 as the ligand, Na2CO3 as the base, PivOH, and DMSO as the additives in dry 1,4-dioxane at 160 °C. These preliminary results indicate the intrinsic catalytic potential of nickel metal for unactivated C(sp3)-H bond arylation.
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15. 15
  For select examples of chelation-assisted Ni-catalyzed C–H alkylation, see:
  (a) Kubo, T.; Chatani, N. Dicumyl Peroxide as a Methylating Reagent in the Ni-Catalyzed Methylation of Ortho C–H Bonds in Aromatic Amides. Org. Lett. 2016, 18, 1698– 1701, DOI: 10.1021/acs.orglett.6b00658
  [ ACS Full Text ], [ CAS], Google Scholar
  15a
  Dicumyl Peroxide as a Methylating Reagent in the Ni-Catalyzed Methylation of Ortho C-H Bonds in Aromatic Amides
  Kubo, Teruhiko; Chatani, Naoto
  Organic Letters (2016), 18 (7), 1698-1701CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
  The direct methylation of ortho C-H bonds in arom. amides, e.g., I (R = OMe, Me, Ph, CN, etc.), with dicumyl peroxide (DCP) using a nickel complex as the catalyst is reported. The reaction shows a high functional group tolerance and is inhibited by radical scavengers. In reactions of meta-substituted arom. amides, the reaction proceeds in a highly selective manner at the less hindered C-H bonds.
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  .
  (b) Aihara, Y.; Chatani, N. Nickel-Catalyzed Direct Alkylation of C–H Bonds in Benzamides and Acrylamides with Functionalized Alkyl Halides via Bidentate-Chelation Assistance. J. Am. Chem. Soc. 2013, 135, 5308– 5311, DOI: 10.1021/ja401344e
  [ ACS Full Text ], [ CAS], Google Scholar
  15b
  Nickel-Catalyzed Direct Alkylation of C-H Bonds in Benzamides and Acrylamides with Functionalized Alkyl Halides via Bidentate-Chelation Assistance
  Aihara, Yoshinori; Chatani, Naoto
  Journal of the American Chemical Society (2013), 135 (14), 5308-5311CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The alkylation of the ortho C-H bonds in benzamides and acrylamides contg. an 8-aminoquinoline moiety as a bidentate directing group with unactivated alkyl halides using nickel complexes as catalysts is described. E.g., in presence of Ni(OTf)2 and PPh3 in toluene, butylation of 8-aminoquinoline deriv. (I) by BuBr gave 81% II. The reaction shows high functional group compatibility. In reactions of meta-substituted arom. amides, the reaction proceeds in a highly selective manner at the less hindered C-H bond.
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  .
  (c) Wu, X.; Zhao, Y.; Ge, H. Nickel-Catalyzed Site-Selective Alkylation of Unactivated C(sp3)–H Bonds. J. Am. Chem. Soc. 2014, 136, 1789– 1792, DOI: 10.1021/ja413131m
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  15c
  Nickel-Catalyzed Site-Selective Alkylation of Unactivated C(sp3)-H Bonds
  Wu, Xuesong; Zhao, Yan; Ge, Haibo
  Journal of the American Chemical Society (2014), 136 (5), 1789-1792CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The direct alkylation of unactivated sp3 C-H bonds of aliph. amides was achieved via nickel catalysis with the assist of a bidentate directing group. The reaction favors the C-H bonds of Me groups over the methylene C-H bonds and tolerates various functional groups. E.g., in presence of Ni(acac)2, 1,2-bis(diphenylphosphino)benzene, and Cs2CO3 in toluene, alkylation of 2-ethyl-2-methyl-N-(quinolin-8-yl)pentanamide with 1-iodopentane gave 89% I. Moreover, this reaction shows a predominant preference for sp3 C-H bonds of Me groups via a five-membered ring intermediate over the sp2 C-H bonds of arenes in the cyclometalation step.
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  (d) Song, W.; Lackner, S.; Ackermann, L. Nickel-Catalyzed C–H Alkylations: Direct Secondary Alkylations and Trifluoroethylations of Arenes. Angew. Chem., Int. Ed. 2014, 53, 2477– 2480, DOI: 10.1002/anie.201309584
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  15d
  Nickel-Catalyzed C-H Alkylations: Direct Secondary Alkylations and Trifluoroethylations of Arenes
  Song, Weifeng; Lackner, Sebastian; Ackermann, Lutz
  Angewandte Chemie, International Edition (2014), 53 (9), 2477-2480CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A versatile nickel catalyst allowed for C-H alkylations of unactivated arenes with challenging secondary alkyl bromides and chlorides. The high catalytic efficacy also set the stage for direct secondary alkylations of indoles as well as C-H trifluoroethylations with ample substrate scope.
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16. 16
  For select examples of chelation-assisted Ni-catalyzed C–H benzylation, see:
  (a) Aihara, Y.; Tobisu, M.; Fukumoto, Y.; Chatani, N. Ni(II)-Catalyzed Oxidative Coupling between C(sp2)–H in Benzamides and C(sp3)–H in Toluene Derivatives. J. Am. Chem. Soc. 2014, 136, 15509– 15512, DOI: 10.1021/ja5095342
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  16a
  Ni(II)-Catalyzed Oxidative Coupling between C(sp2)-H in Benzamides and C(sp3)-H in Toluene Derivatives
  Aihara, Yoshinori; Tobisu, Mamoru; Fukumoto, Yoshiya; Chatani, Naoto
  Journal of the American Chemical Society (2014), 136 (44), 15509-15512CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Oxidative coupling between C(sp2)-H bonds and C(sp3)-H bonds is achieved by the Ni(II)-catalyzed reaction of benzamides contg. an 8-aminoquinoline moiety as the directing group with toluene derivs. in the presence of heptafluoroisopropyl iodide as the oxidant. The method has a broad scope and shows high functional group compatibility e. g., I. Toluene derivs. can be used as the coupling partner in an unreactive solvent.
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  .
  (b) Soni, V.; Khake, S. M.; Punji, B. Nickel-Catalyzed C(sp2)–H/C(sp3)–H Oxidative Coupling of Indoles with Toluene Derivatives. ACS Catal. 2017, 7, 4202– 4208, DOI: 10.1021/acscatal.7b01044
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  16b
  Nickel-Catalyzed C(sp2)-H/C(sp3)-H Oxidative Coupling of Indoles with Toluene Derivatives
  Soni, Vineeta; Khake, Shrikant M.; Punji, Benudhar
  ACS Catalysis (2017), 7 (6), 4202-4208CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Nickel-catalyzed oxidative C(sp2)-H/C(sp3)-H coupling of indoles with toluene derivs. is successfully achieved in the presence of 2-iodobutane as the oxidant. This method allows the selective C-2 benzylation of indoles with toluene derivs. over the alkylation with 2-iodobutane and permits the coupling of diversified indoles via the monochelation assistance. The reaction proceeded through a single-electron-transfer (SET) process, wherein both the C-H nickelation of indole and the C-H activation of toluene derivs. have a significant effect on the entire reaction rate. The synthetic utility of this nickel-catalyzed protocol is demonstrated by the facile removal of the directing group and by the convenient synthesis of the melatonin receptor antagonist Luzindole derivs.
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17. 17
  For select examples of chelation-assisted Ni-catalyzed C–H thiolation, see:
  (a) Yan, S.-Y.; Liu, Y.-J.; Liu, B.; Liu, Y.-H.; Shi, B.-F. Nickel-catalyzed thiolation of unactivated aryl C–H bonds: efficient access to diverse aryl sulfides. Chem. Commun. 2015, 51, 4069– 4072, DOI: 10.1039/C4CC10446C
  [ Crossref], [ PubMed], [ CAS], Google Scholar
  17a
  Nickel-catalyzed thiolation of unactivated aryl C-H bonds: efficient access to diverse aryl sulfides
  Yan, Sheng-Yi; Liu, Yue-Jin; Liu, Bin; Liu, Yan-Hua; Shi, Bing-Feng
  Chemical Communications (Cambridge, United Kingdom) (2015), 51 (19), 4069-4072CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  A nickel-catalyzed thiolation of unactivated C(sp2)-H bonds with disulfides employing the PIP directing group was described. This process uses a catalytic nickel catalyst and no metallic oxidants or cocatalysts are required. The reaction tolerates various important functional groups and heteroarenes, providing an efficient synthetic pathway to access diverse diaryl sulfides.
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  .
  (b) Yan, S.-Y.; Liu, Y.-J.; Liu, B.; Liu, Y.-H.; Zhang, Z.-Z.; Shi, B.-F. Nickel-catalyzed direct thiolation of unactivated C(sp3)–H bonds with disulfides. Chem. Commun. 2015, 51, 7341– 7344, DOI: 10.1039/C5CC01436K
  [ Crossref], [ PubMed], [ CAS], Google Scholar
  17b
  Nickel-catalyzed direct thiolation of unactivated C(sp3)-H bonds with disulfides
  Yan, Sheng-Yi; Liu, Yue-Jin; Liu, Bin; Liu, Yan-Hua; Zhang, Zhuo-Zhuo; Shi, Bing-Feng
  Chemical Communications (Cambridge, United Kingdom) (2015), 51 (34), 7341-7344CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  The first nickel-catalyzed thiolation of unactivated C(sp3)-H bonds with disulfides was described. This transformation uses (dppp)NiCl2 as a catalyst and BINOL as a ligand, which are efficient for the thiolation of β-Me C(sp3)-H bonds of a broad range of aliph. carboxamides. The reaction provides an efficient synthetic pathway to access diverse thioethers.
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  .
  (c) Lin, C.; Li, D.; Wang, B.; Yao, J.; Zhang, Y. Direct ortho-Thiolation of Arenes and Alkenes by Nickel Catalysis. Org. Lett. 2015, 17, 1328– 1331, DOI: 10.1021/acs.orglett.5b00337
  [ ACS Full Text ], [ CAS], Google Scholar
  17c
  Direct ortho-Thiolation of Arenes and Alkenes by Nickel Catalysis
  Lin, Cong; Li, Danyang; Wang, Binjie; Yao, Jinzhong; Zhang, Yuhong
  Organic Letters (2015), 17 (5), 1328-1331CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
  The direct thiolation of 8-quinonlinyl-substituted arenes and alkenes with diaryl disulfides was developed with nickel catalysis. The reaction displayed exceptional compatibility with a wide range of functional groups to regioselectively give the diaryl sulfides and alkenyl sulfides in high yields. E.g., in presence of NiCl2, Na2CO3, TBAI and o-nitrobenzoic acid in DMSO under N2, thiolation of 8-quinonlinyl-substituted arene I with 4-MeOC6H4SSC6H4OMe-4 gave 92% thioether II.
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  (d) Reddy, V. P.; Qiu, R.; Iwasaki, T.; Kambe, N. Nickel-catalyzed synthesis of diaryl sulfides and sulfones via C–H bond functionalization of arylamides. Org. Biomol. Chem. 2015, 13, 6803– 6813, DOI: 10.1039/C5OB00149H
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  17d
  Nickel-catalyzed synthesis of diarylsulfides and sulfones via C-H bond functionalization of arylamides
  Reddy, Vutukuri Prakash; Qiu, Renhua; Iwasaki, Takanori; Kambe, Nobuaki
  Organic & Biomolecular Chemistry (2015), 13 (24), 6803-6813CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
  The direct sulfenylation and sulfonylation of (sp2)C-H bonds of benzamide derivs. were achieved using a Ni catalyst with the aid of an 8-aminoquinoline moiety as a bidentate directing group. These protocols represent a convenient route for the formation of valuable diaryl sulfides and sulfones in moderate to excellent yields.
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18. 18
  Aihara, Y.; Chatani, N. Nickel-Catalyzed Reaction of C–H Bonds in Amides with I2: ortho-Iodination via the Cleavage of C(sp2)–H Bonds and Oxidative Cyclization to β-Lactams via the Cleavage of C(sp3)–H Bonds. ACS Catal. 2016, 6, 4323– 4329, DOI: 10.1021/acscatal.6b00964
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  18
  Nickel-Catalyzed Reaction of C-H Bonds in Amides with I2: ortho-Iodination via the Cleavage of C(sp2)-H Bonds and Oxidative Cyclization to β-Lactams via the Cleavage of C(sp3)-H Bonds
  Aihara, Yoshinori; Chatani, Naoto
  ACS Catalysis (2016), 6 (7), 4323-4329CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  The first example of the nickel(II)-catalyzed reaction of amides using inexpensive and milder mol. iodine (I2) as an iodinating reagent is reported. The reaction of arom. amides having an 8-amino-5-choloroquinoline as a directing group with I2 resulted in the prodn. of ortho-iodination products. Deuterium labeling expts. indicate that the cleavage of C-H bonds is irreversible and is likely the rate-detg. step, which is in sharp contrast to the previously reported transformation using the same Ni(II) catalyst/8-aminoquinoline chelation system. The reaction is applicable to the synthesis of β-lactams from aliph. amides as the substrate, in which C(sp3)-H bonds are activated. The results of deuterium labeling expts. indicate that the cleavage of C(sp3)-H bonds is also irreversible.
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19. 19
  Nakao, Y.; Morita, E.; Idei, H.; Hiyama, T. Dehydrogenative [4 + 2] Cycloaddition of Formamides with Alkynes through Double C–H Activation. J. Am. Chem. Soc. 2011, 133, 3264– 3267, DOI: 10.1021/ja1102037
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  19
  Dehydrogenative [4 + 2] Cycloaddition of Formamides with Alkynes through Double C-H Activation
  Nakao, Yoshiaki; Morita, Eiji; Idei, Hiroaki; Hiyama, Tamejiro
  Journal of the American Chemical Society (2011), 133 (10), 3264-3267CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Formamides having 1-arylalkyl groups, e.g., I, on nitrogen undergo an unprecedented dehydrogenative [4 + 2] cycloaddn. reaction with alkynes via nickel/AlMe3 cooperative catalysis to give highly substituted dihydropyridone derivs., e.g., II, in good yields. Notably, the transformation proceeds through double functionalization of C(sp2)-H and C(sp3)-H bonds in the formamides.
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20. 20
  (a) Lin, C.; Chen, Z.; Liu, Z.; Zhang, Y. Nickel-Catalyzed Stereoselective Alkenylation of C(sp3)–H Bonds with Terminal Alkynes. Org. Lett. 2017, 19, 850– 853, DOI: 10.1021/acs.orglett.6b03856
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  20a
  Nickel-Catalyzed Stereoselective Alkenylation of C(sp3)-H Bonds with Terminal Alkynes
  Lin, Cong; Chen, Zhengkai; Liu, Zhanxiang; Zhang, Yuhong
  Organic Letters (2017), 19 (4), 850-853CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
  A nickel-catalyzed stereoselective alkenylation of an unactivated β-C(sp3)-H bonds in aliph. amides with terminal alkynes using 8-aminoquinoline auxiliary is reported for the first time. This reaction displays excellent functional group tolerance with respect to both aliph. amides and terminal alkynes and features a cheap nickel catalytic system. The 8-aminoquinolyl directing group could be smoothly removed, and the resultant β-styrylcarboxylic acid derivs. could serve as versatile building blocks for further transformation.
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  .
  (b) Li, M.; Yang, Y.; Zhou, D.; Wan, D.; You, J. Nickel-Catalyzed Addition-Type Alkenylation of Unactivated, Aliphatic C–H Bonds with Alkynes: A Concise Route to Polysubstituted γ-Butyrolactones. Org. Lett. 2015, 17, 2546– 2549, DOI: 10.1021/acs.orglett.5b01128
  [ ACS Full Text ], [ CAS], Google Scholar
  20b
  Nickel-Catalyzed Addition-Type Alkenylation of Unactivated, Aliphatic C-H Bonds with Alkynes: A Concise Route to Polysubstituted γ-Butyrolactones
  Li, Mingliang; Yang, Yudong; Zhou, Danni; Wan, Danyang; You, Jingsong
  Organic Letters (2015), 17 (10), 2546-2549CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
  Through the nickel-catalyzed chelation-assisted C-H bond activation strategy, the addn.-type alkenylation of unreactive β-C(sp3)-H bonds of aliph. amides with internal alkynes is developed for the first time to produce γ,δ-unsatd. carboxylic amide derivs. [e.g., amide I + PhC≡CPh → γ,δ-unsatd. amide II (78% optimized, E/Z 1/2.8) using Ni(OAc)2 and PPh3 in i-PrOH/toluene]. The resulting alkenylated products can further be transformed into polysubstituted γ-butyrolactones with pyridinium chlorochromate (PCC) [e.g., III → IV (78%)].
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  .
  (c) Maity, S.; Agasti, S.; Earsad, A. M.; Hazra, A.; Maiti, D. Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient Olefins into Unactivated sp3 C–H Bonds. Chem. - Eur. J. 2015, 21, 11320– 11324, DOI: 10.1002/chem.201501962
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  20c
  Nickel-Catalyzed Insertion of Alkynes and Electron-Deficient Olefins into Unactivated sp3 C-H Bonds
  Maity, Soham; Agasti, Soumitra; Earsad, Arif Mahammad; Hazra, Avijit; Maiti, Debabrata
  Chemistry - A European Journal (2015), 21 (32), 11320-11324CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Insertion of unsatd. systems such as alkynes and olefins into unactivated sp3 C-H bonds remains an unexplored problem. This issue was addressed by successfully incorporating a wide variety of functionalized alkynes and electron-deficient olefins into the unactivated sp3 C-H bond of pivalic acid derivs. with excellent syn- and linear- selectivity. A strongly chelating 8-aminoquinoline directing group proved beneficial for these insertion reactions, while an air-stable and inexpensive Ni(II) salt was employed as the active catalyst.
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  (d) Liu, Y.-H.; Liu, Y.-J.; Yan, S.-Y.; Shi, B.-F. Ni(II)-catalyzed dehydrative alkynylation of unactivated (hetero)aryl C–H bonds using oxygen: a user-friendly approach. Chem. Commun. 2015, 51, 11650– 11653, DOI: 10.1039/C5CC03729H
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  20d
  Ni(II)-catalyzed dehydrative alkynylation of unactivated (hetero)aryl C-H bonds using oxygen: a user-friendly approach
  Liu, Yan-Hua; Liu, Yue-Jin; Yan, Sheng-Yi; Shi, Bing-Feng
  Chemical Communications (Cambridge, United Kingdom) (2015), 51 (58), 11650-11653CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Ni(II)-catalyzed dehydrative alkynylation of unactivated C(sp2)-H bonds with terminal alkynes under atm. pressure of oxygen was developed. This reaction features the use of catalytic amts. of nickel as the catalyst and O2 as the sole oxidant, providing a user-friendly approach to the synthesis of aryl alkynes.
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21. 21
  For C–H functionalization reactions where alkyne or alkene act as hydrogen acceptor, see:
  (a) Inoue, S.; Shiota, H.; Fukumoto, Y.; Chatani, N. Ruthenium-Catalyzed Carbonylation at Ortho C–H Bonds in Aromatic Amides Leading to Phthalimides: C–H Bond Activation Utilizing a Bidentate System. J. Am. Chem. Soc. 2009, 131, 6898– 6899, DOI: 10.1021/ja900046z
  [ ACS Full Text ], [ CAS], Google Scholar
  21a
  Ruthenium-Catalyzed Carbonylation at Ortho C-H Bonds in Aromatic Amides Leading to Phthalimides: C-H Bond Activation Utilizing a Bidentate System
  Inoue, Satoshi; Shiota, Hirotaka; Fukumoto, Yoshiya; Chatani, Naoto
  Journal of the American Chemical Society (2009), 131 (20), 6898-6899CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A new type of carbonylation of the ortho C-H bonds in arom. amides, e.g., I, in which the pyridin-2-ylmethylamino moiety functions as a bidentate directing group, can be achieved to generate phthalimide derivs. such as II. The presence of ethylene as a hydrogen acceptor and also of H2O, probably for the generation of an active catalytic species, is required. A wide variety of functional groups, including methoxy, amino, ester, ketone, cyano, chloro, and even bromo substituents, are tolerated as substituents on the arom. amides. A dinuclear ruthenium complex contg. two amide ligands was isolated by the stoichiometric reaction of I and Ru3(CO)12, in which I binds to one Ru atom in the expected N,N fashion and the carbonyl oxygen binds to the other Ru atom as an O donor.
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  .
  (b) Hasegawa, N.; Charra, V.; Inoue, S.; Fukumoto, Y.; Chatani, N. Highly Regioselective Carbonylation of Unactivated C(sp3)–H Bonds by Ruthenium Carbonyl. J. Am. Chem. Soc. 2011, 133, 8070– 8073, DOI: 10.1021/ja2001709
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  21b
  Highly Regioselective Carbonylation of Unactivated C(sp3)-H Bonds by Ruthenium Carbonyl
  Hasegawa, Nao; Charra, Valentine; Inoue, Satoshi; Fukumoto, Yoshiya; Chatani, Naoto
  Journal of the American Chemical Society (2011), 133 (21), 8070-8073CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The regioselective carbonylation of unactivated C(sp3)-H bonds of aliph. amides was achieved using Ru3(CO)12 as a catalyst. The presence of a 2-pyridinylmethylamine moiety in the amide is crucial for a successful reaction. The reaction shows a preference for C-H bonds of Me groups as opposed to methylene C-H bonds and tolerates a variety of functional groups. The stoichiometric reaction of an amide with Ru3(CO)12 gave a dinuclear ruthenium complex in which the 2-pyridinylmethylamino moiety was coordinated to the ruthenium center in an N,N manner.
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  (c) Song, W.; Ackermann, L. Nickel-catalyzed alkyne annulation by anilines: versatile indole synthesis by C–H/N–H functionalization. Chem. Commun. 2013, 49, 6638– 6640, DOI: 10.1039/c3cc43915a
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  21c
  Nickel-catalyzed alkyne annulation by anilines: versatile indole synthesis by C-H/N-H functionalization
  Song, Weifeng; Ackermann, Lutz
  Chemical Communications (Cambridge, United Kingdom) (2013), 49 (59), 6638-6640CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  Versatile nickel catalysts enabled the step-economical synthesis of decorated indoles through alkyne annulations with anilines bearing removable directing groups. E.g., in presence of Ni(cod)2 and dppf, annulation of PhC≡CPh with N-(2-pyrimidinyl)aniline gave 81% indole deriv. (I). The C-H/N-H activation strategy efficiently occurred in the absence of any metal oxidants and with excellent selectivities.
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  (d) Obata, A.; Ano, Y.; Chatani, N. Nickel-catalyzed C–H/N–H annulation of aromatic amides with alkynes in the absence of a specific chelation system. Chem. Sci. 2017, 8, 6650– 6655, DOI: 10.1039/C7SC01750B
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  21d
  Nickel-catalyzed C-H/N-H annulation of aromatic amides with alkynes in the absence of a specific chelation system
  Obata, Atsushi; Ano, Yusuke; Chatani, Naoto
  Chemical Science (2017), 8 (9), 6650-6655CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  The Ni-catalyzed reaction of arom. amides 4-H3COC6H4NHC(O)R (R = 4-fluorophenyl, 1-naphthyl, 2-furyl, etc.) with alkynes such as diphenylacetylene, 1-phenyl-1-propyne, 4-octyne, etc. in the presence of KOBut involves C-H/N-H oxidative annulation to give 1(2H)-isoquinolinones, e.g., I. A key to the success of the reaction is the use of a catalytic amt. of strong base, such as KOBut. The reaction shows a high functional group compatibility. The reaction with unsym. alkynes, such as 1-arylalkynes, gives the corresponding 1(2H)-isoquinolinones with a high level of regioselectivity. This discovery would lead to the development of Ni-catalyzed chelation-assisted C-H functionalization reactions without the need for a specific chelation system.
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22. 22
  For Rh-catalyzed C–H functionalization with internal alkyne, see:
  (a) Mochida, S.; Nobuyoshi, U.; Koji, H.; Tetsuya, S.; Masahiro, M. Rhodium-catalyzed Oxidative Coupling/Cyclization of Benzamides with Alkynes via C–H Bond Cleavage. Chem. Lett. 2010, 39, 744– 746, DOI: 10.1246/cl.2010.744
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  22a
  Rhodium-catalyzed oxidative coupling/cyclization of benzamides with alkynes via C-H bond cleavage
  Mochida, Satoshi; Umeda, Nobuyoshi; Hirano, Koji; Satoh, Tetsuya; Miura, Masahiro
  Chemistry Letters (2010), 39 (7), 744-746CODEN: CMLTAG; ISSN:0366-7022. (Chemical Society of Japan)
  An oxidative coupling of primary, secondary, and tertiary benzamides with internal alkynes proceeds efficiently under rhodium catalysis was studied and the synthesis of the target compds. was achieved selectively providing the corresponding 1:1 and 1:2 coupling products, accompanied by C-H and/or N-H bond cleavages. Some of the products exhibit intense fluorescence in the solid state. The products thus obtained included N,N-dimethyl-5,6,7,8-tetraphenyl-1-naphthalenecarboxamide, 5,6,13-triphenyl-8H-dibenzo[a,g]quinolizin-8-one derivs. and 2,3,4-triphenyl-1(2H)-isoquinolinone derivs.
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  .
  (b) Hyster, T. K.; Rovis, T. Rhodium-Catalyzed Oxidative Cycloaddition of Benzamides and Alkynes via C–H/N–H Activation. J. Am. Chem. Soc. 2010, 132, 10565– 10569, DOI: 10.1021/ja103776u
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  22b
  Rhodium-Catalyzed Oxidative Cycloaddition of Benzamides and Alkynes via C-H/N-H Activation
  Hyster, Todd K.; Rovis, Tomislav
  Journal of the American Chemical Society (2010), 132 (30), 10565-10569CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The oxidative cycloaddn. of benzamides and alkynes has been developed. The reaction utilizes Rh(III) catalysts in the presence of Cu(II) oxidants, and is proposed to proceed by N-H metalation of the amide followed by ortho C-H activation. The resultant rhodacycle undergoes alkyne insertion to form isoquinolones in good yield. The reaction is tolerant of extensive substitution on the amide, alkyne, and arene, including halides, silyl ethers, and unprotected aldehydes as substituents. Unsym. alkynes proceed with excellent regioselectivity, and heteroaryl carboxamides are tolerated leading to intriguing scaffolds for medicinal chem. A series of competition expts. shed further light on the mechanism of the transformation and reasons for selectivity.
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  (c) Guimond, N.; Gorelsky, S. I.; Fagnou, K. Rhodium(III)-Catalyzed Heterocycle Synthesis Using an Internal Oxidant: Improved Reactivity and Mechanistic Studies. J. Am. Chem. Soc. 2011, 133, 6449– 6457, DOI: 10.1021/ja201143v
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  22c
  Rhodium(III)-Catalyzed Heterocycle Synthesis Using an Internal Oxidant: Improved Reactivity and Mechanistic Studies
  Guimond, Nicolas; Gorelsky, Serge I.; Fagnou, Keith
  Journal of the American Chemical Society (2011), 133 (16), 6449-6457CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Directing groups that can act as internal oxidants have recently been shown to be beneficial in metal-catalyzed heterocycle syntheses that undergo C-H functionalization. Pursuant to the rhodium(III)-catalyzed redox-neutral isoquinolone synthesis that we recently reported, we present in this article the development of a more reactive internal oxidant/directing group that can promote the formation of a wide variety of isoquinolones at room temp. while employing low catalyst loadings (0.5 mol %). In contrast to previously reported oxidative rhodium(III)-catalyzed heterocycle syntheses, the new conditions allow for the first time the use of terminal alkynes. Also, it is shown that the use of alkenes, including ethylene, instead of alkynes leads to the room temp. formation of 3,4-dihydroisoquinolones. Mechanistic investigations of this new system point to a change in the turnover limiting step of the catalytic cycle relative to the previously reported conditions. Concerted metalation-deprotonation (CMD) is now proposed to be the turnover limiting step. In addn., DFT calcns. conducted on this system agree with a stepwise C-N bond reductive elimination/N-O bond oxidative addn. mechanism to afford the desired heterocycle. Concepts highlighted by the calcns. were found to be consistent with exptl. results.
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  (d) Hyster, T. K.; Rovis, T. An improved catalyst architecture for rhodium(III) catalyzed C–H activation and its application to pyridone synthesis. Chem. Sci. 2011, 2, 1606– 1610, DOI: 10.1039/C1SC00235J
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  22d
  An improved catalyst architecture for rhodium(III) catalyzed C-H activation and its application to pyridone synthesis
  Hyster, Todd K.; Rovis, Tomislav
  Chemical Science (2011), 2 (8), 1606-1610CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  The authors have developed a method for prepg. pyridones from the coupling reaction of acrylamides and alkynes with either stoichiometric Cu(OAc)2 or catalytic Cu(OAc)2 and air as oxidants. In these studies, a larger ligand, 1,3-di-tert-butylcyclopentadienyl (termed Cpt) results in higher degrees of regioselectivity in the alkyne insertion event. The transformation tolerates a broad variety of alkynes and acrylamides. Also, Cpt and Cp* demonstrate similar catalytic activity. This similarity allows for mechanistic studies to be undertaken which suggest a difference in mechanism between this reaction and the previously studied benzamide system.
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  .
  (e) Shan, G.; Flegel, J.; Li, H.; Merten, C.; Ziegler, S.; Antonchick, A. P.; Waldmann, H. C–H Bond Activation for the Synthesis of Heterocyclic Atropisomers Yields Hedgehog Pathway Inhibitors. Angew. Chem., Int. Ed. 2018, 57, 14250– 14254, DOI: 10.1002/anie.201809680
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  C-H Bond Activation for the Synthesis of Heterocyclic Atropisomers Yields Hedgehog Pathway Inhibitors
  Shan, Gang; Flegel, Jana; Li, Houhua; Merten, Christian; Ziegler, Slava; Antonchick, Andrey P.; Waldmann, Herbert
  Angewandte Chemie, International Edition (2018), 57 (43), 14250-14254CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  In the presence of a nonracemic cyclopentenopyridine rhodium complex, O-(arylpentynyl) arylhydroxamates such as I underwent enantioselective C-H activation and cyclization reactions mediated by dibenzoyl peroxide and CsOAc in 2-chloroethanol/1,2-dichloroethane to yield atropisomeric arylisoquinolinones such as II in 45-95% yields and in 78:22-96:4 er. Five of the arylisoquinolinone products (including II) inhibited the Hedgehog pathway in human cells; one of the compds. tested inhibited the Hedgehog pathway but did not displace labeled cyclopamine from Smoothened, implying that at least one of the arylisoquinolinones does not inhibit the Hedgehog pathway through binding to Smoothened.
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  (f) Shibata, K.; Natsui, S.; Chatani, N. Rhodium-Catalyzed Alkenylation of C–H Bonds in Aromatic Amides with Alkynes. Org. Lett. 2017, 19, 2234– 2237, DOI: 10.1021/acs.orglett.7b00709
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  22f
  Rhodium-Catalyzed Alkenylation of C-H Bonds in Aromatic Amides with Alkynes
  Shibata, Kaname; Natsui, Satoko; Chatani, Naoto
  Organic Letters (2017), 19 (9), 2234-2237CODEN: ORLEF7; ISSN:1523-7052. (American Chemical Society)
  The rhodium-catalyzed alkenylation of C-H bonds of arom. amides with alkynes is reported. A variety of functional groups, including OMe, OAc, Br, Cl, and even NO2, are applicable to this reaction to give the corresponding hydroarylation products. The presence of an 8-aminoquinoline group as the directing group is crucial for the success of the reaction.
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23. 23
  For Ru-catalyzed C–H functionalization with internal alkynes, see:
  (a) Allu, S.; Swamy, K. C. K. Ruthenium-Catalyzed Synthesis of Isoquinolones with 8-Aminoquinoline as a Bidentate Directing Group in C–H Functionalization. J. Org. Chem. 2014, 79, 3963– 3972, DOI: 10.1021/jo500424p
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  23a
  Ruthenium-Catalyzed Synthesis of Isoquinolones with 8-Aminoquinoline as a Bidentate Directing Group in C-H Functionalization
  Allu, Srinivasarao; Swamy, K. C. Kumara
  Journal of Organic Chemistry (2014), 79 (9), 3963-3972CODEN: JOCEAH; ISSN:0022-3263. (American Chemical Society)
  Ruthenium-catalyzed oxidative annulation of N-quinolin-8-yl-benzamides with alkynes in open air has been achieved using 8-aminoquinolinyl moiety as a bidentate directing group in the presence of Cu(OAc)2·H2O as an oxidant. This reaction offers a broad substrate scope, and both sym. and unsym. alkynes can be applied. High regioselectivity was achieved in the case of unsym. (aryl)alkynes. Reaction with heteroaryl amides was also successful in this catalytic process. A ruthenium-N-quinolin-8-yl-benzamide complex was isolated in the absence of alkyne; in the absence of both N-quinolin-8-yl-benzamide and alkyne, in contrast to literature, only the monoacetate complex RuCl(OAc)(p-cymene), but not the bis-acetate complex Ru(OAc)2(p-cymene), was isolated. These data suggest that this reaction may proceed via N,N-bidentate chelate complex. Key products were characterized by X-ray crystallog.
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  (b) Kaishap, P. P.; Duarah, G.; Chetiab, D.; Gogoi, S. Ru(II)-Catalyzed annulation of benzamidines and alkynes by C–H/N–H activation: a facile synthesis of 1-aminoisoquinolines. Org. Biomol. Chem. 2017, 15, 3491– 3498, DOI: 10.1039/C7OB00389G
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  Ru()-Catalyzed annulation of benzamidines and alkynes by C-H/N-H activation: a facile synthesis of 1-aminoisoquinolines
  Kaishap, P. P.; Duarah, G.; Chetia, D.; Gogoi, S.
  Organic & Biomolecular Chemistry (2017), 15 (16), 3491-3498CODEN: OBCRAK; ISSN:1477-0520. (Royal Society of Chemistry)
  An inexpensive Ru(II) complex catalyzes the oxidative annulation reaction of disubstituted alkynes with benzamidines to provide highly valuable 1-aminoisoquinolines in high yields. The reaction also features excellent regioselectivity with some unsym. alkynes.
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24. 24
  For Pd-catalyzed C–H functionalization with internal alkynes, see:
  (a) Shu, Z.; Guo, Y.; Li, W.; Wang, B. Pd/C-catalyzed synthesis of N-aryl and N-alkyl isoquinolones via CH/NH activation. Catal. Today 2017, 297, 292– 297, DOI: 10.1016/j.cattod.2017.02.005
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  Pd/C-catalyzed synthesis of N-aryl and N-alkyl isoquinolones via C-H/N-H activation
  Shu, Zhen; Guo, Yuntao; Li, Wei; Wang, Baiquan
  Catalysis Today (2017), 297 (), 292-297CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)
  Pd/C-catalyzed direct synthesis of N-aryl and N-alkyl isoquinolones was developed via the annulation reactions of benzamides and alkynes in high yields (up to 99%) through the cleavage of C-H/N-H bonds. The reaction was ligand-free and air was used as oxidant. High regioselectivities were found when unsym. alkynes or meta-benzamides were used as substrates. The heterocyclic carboxamide substrates, such as furan and thiophene derivs., also afforded the corresponding products in high yields.
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  (b) Sharma, N.; Saha, R.; Parveen, N.; Sekar, G. Palladium-Nanoparticles-Catalyzed Oxidative Annulation of Benzamides with Alkynes for the Synthesis of Isoquinolones. Adv. Synth. Catal. 2017, 359, 1947– 1958, DOI: 10.1002/adsc.201601137
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  Palladium-Nanoparticles-Catalyzed Oxidative Annulation of Benzamides with Alkynes for the Synthesis of Isoquinolones
  Sharma, Nidhi; Saha, Rajib; Parveen, Naziya; Sekar, Govindasamy
  Advanced Synthesis & Catalysis (2017), 359 (11), 1947-1958CODEN: ASCAF7; ISSN:1615-4150. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A novel method to synthesize isoquinolones I (R1 = H, 6,7-(CH3)2, 6-OC2H5, etc.; R2 = CH3, C2H5, CH2C6H5; R3 = R4 = C6H5, 4-H3CC6H4, 3-FC6H4, etc.; R3 = C6H5, 4-H3CC6H4, 4-CH3OC6H4; R4 = CH3, C6H5) via oxidative annulation of N-alkoxy benzamides and alkynes using binaphthyl-stabilized palladium nanoparticles (Pd-BNP) as catalyst has been developed. This methodol. affords various isoquinolone derivs. in good to excellent yields with high regioselectivities in the presence of air as oxidant. N-Methoxybenzothioamide was also found to underwent oxidative annulation with alkyne successfully and provided a sulfur analog of isoquinolones II (R1 = R2 = H, 3-CH3, 3-F, 4-F) in moderate yields. The Pd-BNP catalyst was easily recovered and reused up to four times without any apparent agglomeration.
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25. 25
  For Co-catalyzed C–H functionalization with internal alkyne, see:
  (a) Grigorjeva, L.; Daugulis, O. Cobalt-catalyzed, aminoquinoline-directed C(sp²)-H bond alkenylation by alkynes. Angew. Chem., Int. Ed. 2014, 53, 10209– 10212, DOI: 10.1002/anie.201404579
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  25a
  Cobalt-catalyzed, aminoquinoline-directed C(sp2)-H bond alkenylation by alkynes
  Grigorjeva, Liene; Daugulis, Olafs
  Angewandte Chemie, International Edition (2014), 53 (38), 10209-10212CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  A method for Co-catalyzed, aminoquinoline- and picolinamide-directed C(sp2)H bond alkenylation by alkynes was developed. The method shows excellent functional-group tolerance and both internal and terminal alkynes are competent substrates for the coupling. The reaction employs a Co(OAc)2.4H2O catalyst, Mn(OAc)2 co-catalyst, and O2 (from air) as a terminal oxidant.
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  (b) Nguyen, T. T.; Grigorjeva, L.; Daugulis, O. Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp2 C–H Bonds. ACS Catal. 2016, 6, 551– 554, DOI: 10.1021/acscatal.5b02391
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  25b
  Cobalt-Catalyzed, Aminoquinoline-Directed Functionalization of Phosphinic Amide sp2 C-H Bonds
  Nguyen, Tung Thanh; Grigorjeva, Liene; Daugulis, Olafs
  ACS Catalysis (2016), 6 (2), 551-554CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  In this paper, authors introduce arylphosphinic acid aminoquinoline amides as competent substrates for cobalt-catalyzed sp2 C-H bond functionalization. Specifically, the feasibility of their coupling with alkynes, alkenes, and allyl pivalate has been demonstrated. Reactions are catalyzed by simple Co(NO3)2 hydrate in ethanol or mixed dioxane/tBuOH solvent in the presence of Mn(OAc)3·2H2O additive, sodium pivalate, or acetate base and use oxygen from the air as an oxidant. Directing group removal affords ortho-functionalized P,P-diarylphosphinic acids.
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  (c) Manoharan, R.; Jeganmohan, M. Cobalt-catalyzed cyclization of benzamides with alkynes: a facile route to isoquinolones with hydrogen evolution. Org. Biomol. Chem. 2018, 16, 8384– 8389, DOI: 10.1039/C8OB01924J
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  Cobalt-catalyzed cyclization of benzamides with alkynes: a facile route to isoquinolones with hydrogen evolution
  Manoharan Ramasamy; Jeganmohan Masilamani
  Organic & biomolecular chemistry (2018), 16 (37), 8384-8389 ISSN:.
  The reaction of benzamides with alkynes assisted by an 8-aminoquinoline ligand in the presence of Co(OAc)2·4H2O and pivalic acid under an air atmosphere provided isoquinolone derivatives in good to excellent yields. In this reaction, the active Co(iii) species is regenerated by the reaction of Co(i) species with pivalic acid under an air atmosphere with hydrogen evolution. The proposed mechanism was supported by competition experiments, deuterium labelling studies, radical scavenger experiments and kinetic studies.
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  (d) Zhai, S.; Qiu, S.; Chen, X.; Wu, J.; Zhao, H.; Tao, C.; Li, Y.; Cheng, B.; Wang, H.; Zhai, H. 2-(1-Methylhydrazinyl)pyridine as a reductively removable directing group in a cobalt-catalyzed C(sp2)–H bond alkenylation/annulation cascade. Chem. Commun. 2018, 54, 98– 101, DOI: 10.1039/C7CC08533H
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  2-(1-Methylhydrazinyl)pyridine as a reductively removable directing group in a cobalt-catalyzed C(sp2)-H bond alkenylation/annulation cascade
  Zhai, Shengxian; Qiu, Shuxian; Chen, Xiaoming; Wu, Jiang; Zhao, Hua; Tao, Cheng; Li, Yun; Cheng, Bin; Wang, Huifei; Zhai, Hongbin
  Chemical Communications (Cambridge, United Kingdom) (2018), 54 (1), 98-101CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)
  We describe a new application of 2-(1-methylhydrazinyl)pyridine as a bidentate directing group to directing cobalt-catalyzed C(sp2)-H alkenylation/annulation of the corresponding benzoic hydrazides to form an isoquinoline backbone, via reacting with a terminal or internal alkyne followed by annulation. The reaction shows a broad substrate scope with the products obtained in good to excellent yields and high regioselectivity. Moreover, the directing group can be reductively removed in one step under mild conditions.
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26. 26
  In the presence of a strong base, such as t-BuOK, N–H deprotonation would form a nickel(0) ate complex. A recent computational study indicates the subsequent C–H metalation from the nickel(0) ate complex occurs via a ligand-to-ligand hydrogen transfer mechanism. See ref (8c).
  There is no corresponding record for this reference.
27. 27
  For select reviews and crystal structures of Ni-hydride complexes, see:
  (a) Eberhardt, N. A.; Guan, H. Nickel Hydride Complexes. Chem. Rev. 2016, 116, 8373– 8426, DOI: 10.1021/acs.chemrev.6b00259
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  27a
  Nickel Hydride Complexes
  Eberhardt, Nathan A.; Guan, Hairong
  Chemical Reviews (Washington, DC, United States) (2016), 116 (15), 8373-8426CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review; nickel hydride complexes, defined herein as any mols. bearing a nickel hydrogen bond, are crucial intermediates in numerous nickel-catalyzed reactions. Some of them are also synthetic models of nickel-contg. enzymes such as [NiFe]-hydrogenase. The overall objective of this review is to provide a comprehensive overview of this specific type of hydride complexes, which has been studied extensively in recent years. This review begins with the significance and a very brief history of nickel hydride complexes, followed by various methods and spectroscopic or crystallog. tools used to synthesize and characterize these complexes. Also discussed are stoichiometric reactions involving nickel hydride complexes and how some of these reactions are developed into catalytic processes.
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  (b) Matson, E. M.; Martinez, G. E.; Ibrahim, A. D.; Jackson, B. J.; Bertke, J. A.; Fout, A. R. Nickel(II) Pincer Carbene Complexes: Oxidative Addition of an Aryl C–H Bond to Form a Ni(II) Hydride. Organometallics 2015, 34, 399– 407, DOI: 10.1021/om5007177
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  27b
  Nickel(II) Pincer Carbene Complexes: Oxidative Addition of an Aryl C-H Bond to Form a Ni(II) Hydride
  Matson, Ellen M.; Espinosa Martinez, Gabriel; Ibrahim, Abdulrahman D.; Jackson, Bailey J.; Bertke, Jeffrey A.; Fout, Alison R.
  Organometallics (2015), 34 (2), 399-407CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  The synthesis and characterization of a series of nickel(II) pincer complexes of the meta-phenylene-bridged bis-N-heterocyclic DIPPCCC ligand framework are reported. Characterization of the Ni(II)Cl complex revealed a square planar species with Cl- and the anionic carbon trans to one another. Formation of Ni(II) alkyl complexes derived from complex 1 was accomplished by addn. of LiR [R = CH3 (2); CH2SiMe3 (3)]. Furthermore, we report a synthetic pathway to access the catalytically relevant Ni(II)H species (DIPPCCC)NiH (4), by direct oxidative addn. of an aryl C-H bond across a Ni(0) center. Complexes 1-4 have been characterized by 1H and 13C NMR and electronic absorption spectroscopies as well as x-ray crystallog.
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  (c) Clement, N. D.; Cavell, K. J.; Jones, C.; Elsevier, C. J. Oxidative Addition of Imidazolium Salts to Ni0 and Pd0: Synthesis and Structural Characterization of Unusually Stable Metal–Hydride Complexes. Angew. Chem., Int. Ed. 2004, 43, 1277
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  Oxidative addition of imidazolium salts to Ni0 and Pd0: Synthesis and structural characterization of unusually stable metal-hydride complexes
  Clement, Nicolas D.; Cavell, Kingsley J.; Jones, Cameron; Elsevier, Cornelis J.
  Angewandte Chemie, International Edition (2004), 43 (10), 1277-1279CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  C-H activation of imidazolium salts by coordinatively unsatd. low-valent Ni and Pd complexes occurs under mild conditions. Surprisingly stable hydrido-metal-N-heterocyclic carbene complexes were isolated, which demonstrates the ease with which imidazolium-based ionic liqs. may react with transition-metal complexes during catalysis. Thus, reaction of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene with Ni(COD)2 in PhMe followed by treatment with 1-butyl-3-methylimidazolium tetrafluoroborate gave 73% title complex, [NiH(bmiy)(dmesiy)2]BF4 (3b), whereas reaction of 1,3-dimethylimidazolium tetrafluoroborate with bis[1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene]palladium in THF/Me2CO gave 62% [PdH(dmiy)(dmesiy)2]BF4 (5). The crystal structures of 3b and 5 were detd.
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28. 28
  Crabtree, R. H. Dihydrogen Complexation. Chem. Rev. 2016, 116, 8750– 8769, DOI: 10.1021/acs.chemrev.6b00037
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  Dihydrogen Complexation
  Crabtree, Robert H.
  Chemical Reviews (Washington, DC, United States) (2016), 116 (15), 8750-8769CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
  A review; dihydrogen complexation with retention of the H-H bond, once an exotic concept, has by now appeared in a very wide range of contexts. Three structural types are currently recognized: Kubas dihydrogen, stretched dihydrogen, and compressed dihydrides. These can be difficult to distinguish, hence the development of a no. of novel spectroscopic methods for doing so, mainly based on NMR spectroscopy. Three important reactivity patterns are identified: proton loss, oxidative addn., and dissocn., each of which often contributes to larger reaction schemes, as in homogeneous hydroformylation. Main group examples are beginning to appear, although here it is mainly by computational studies that the relevant structures can be identified. Enzymes such as the hydrogenases and nitrogenases are also proposed to involve these structures.
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29. 29
  (a) She, L.; Li, X.; Sun, H.; Ding, J.; Frey, M.; Klein, H.-F. Insertion of Alkynes into Ni–H Bonds: Synthesis of Novel Vinyl Nickel(II) and Dinuclear Vinyl Nickel(II) Complexes Containing a [P, S]-Ligand. Organometallics 2007, 26, 566– 570, DOI: 10.1021/om0606340
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  29a
  Insertion of Alkynes into Ni-H Bonds: Synthesis of Novel Vinyl Nickel(II) and Dinuclear Vinyl Nickel(II) Complexes Containing a [P, S]-Ligand
  She, Lei; Li, Xiaoyan; Sun, Hongjian; Ding, Jun; Frey, Markus; Klein, Hans-Friedrich
  Organometallics (2007), 26 (3), 566-570CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Reactions of alkynes with Ni hydride complexes bearing a [P, S]-ligand and supported by trimethylphosphine were studied. Tetracoordinate vinyl Ni(II) complexes [(L)Ni[C(:CH2)Ph]PMe3] (3; LH = o-Ph2PC6H4SH), [(L)Ni[C(:CH2)SiMe3]PMe3] (5) and [(L)Ni[C(:CH2)Bu]PMe3] (6) with square-planar geometry were obtained in 47-64% yields by reaction of phenylacetylene, trimethylsilylacetylene, and 1-hexyne with the hydrido Ni complex [(L)Ni(PMe3)2H] (1), resp. Reaction of 1,4-bis(trimethylsilylethynyl)benzene with complex 1 proceeds as a mono-insertion and afforded 76% [(L)Ni[C(:CHSiMe3)C6H4C≡CSiMe3-p]PMe3] (7) as a 4:1 mixt. of Z and E isomers, while reaction of 1,4-bis(ethynyl)benzene with 1 leads to the dinuclear vinyl Ni(II) complex [p-(L)Ni(PMe3)C(:CH2)C6H4C(:CH2)Ni(L)PMe3] (8) in 30% yield.
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  (b) Zhou, H.; Sun, H.; Zheng, T.; Zhang, S.; Li, X. Synthesis of Vinylnickel and Nickelacyclopropane Complexes Containing a Chelate [P,Se]-Ligand. Eur. J. Inorg. Chem. 2015, 3139– 3145, DOI: 10.1002/ejic.201500293
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  29b
  Synthesis of vinylnickel and nickelacyclopropane complexes containing a chelate [P,Se]-ligand
  Zhou, Hongwei; Sun, Hongjian; Zheng, Tingting; Zhang, Shumiao; Li, Xiaoyan
  European Journal of Inorganic Chemistry (2015), 2015 (19), 3139-3145CODEN: EJICFO; ISSN:1434-1948. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Nickel(II) selenolate hydride complex [Ph2P(1,2-C6H4)SeNiH(PMe3)2] (1) was prepd. by oxidative addn. of 2-(diphenylphosphino)benzeneselenol 2-Ph2PC6H4SeH with Ni(PMe3)4. The insertion reactions of 1 with alkynes RC≡CR1 gave vinylnickel complexes [Ph2P(1,2-C6H4)SeNi(CR:CHR1)(PMe3)] (2, R = Ph, R1 = H; 3, R = Me, R1 = Ph). The phosphoranylidene-substituted nickelacyclopropane complexes [(2-Ph2PC6H4Se)Ni(Me3P:CPh-CHPh)] (4), [(2-Ph2PC6H4Se)Ni(Me3P:CTMS-CH2)] (5) [(2-Ph2PC6H4Se)Ni(Me3P:CPh-CHTMS)] (6A) and [(2-Ph2PC6H4Se)Ni(Me3P:CTMS-CHPh)] (6B), contg. an ylidic ligand were obtained by reacting diphenylacetylene, (trimethylsilyl)acetylene, and 1-phenyl-2-(trimethylsilyl)acetylene with 1. The mol. structures of 1-5 were detd. by single-crystal x-ray diffraction.
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  29c
  Vinyl/Phenyl Exchange Reaction within Vinyl Nickel Complexes Bearing Chelate [P, S]-Ligands
  Xue, Benjing; Sun, Hongjian; Ren, Shishuai; Li, Xiaoyan; Fuhr, Olaf
  Organometallics (2017), 36 (21), 4246-4255CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Three Ni(II) hydrides, [2-Ph2P(4-Me-C6H3)S]NiH(PMe3)2 (1), [2-Ph2P(6-Me3Si-C6H3)S]NiH(PMe3)2 (2), and [2-Ph2P(4-Me3Si -C6H3)S]NiH(PMe3)2 (3), were synthesized via S-H bond activation through the reaction of Ni(PMe3)4 with (2-diphenylphosphanyl)thiophenols. The reactions of Ni(II) hydrides (1-3) with different alkynes were studied. Although the 1st step is the insertion of alkyne into the Ni-H bond for each reaction, different final products were isolated. Normal vinyl Ni complex [2-Ph2P(4-Me-C6H3)S]Ni(CPh:CH2)(PMe3) (4) was obtained by the reaction of phenylacetylene with 1. The nickelacyclopropane complexes [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CH2] (5), [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CH2] (6), [2-Ph2P(4-Me3-C6H3)S]Ni[Ph(PMe3)C-CHPh] (7), [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CHPh] (8), [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CHPh] (9), [2-Ph2P(4-Me-C6H3)S]Ni[Ph(PMe3)C-CHSiMe3] (10) or [2-Ph2P(4-Me-C6H3)S]Ni[Me3Si(PMe3)C-CHPh] (10), [2-Ph2P(6-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CHSiMe3] (11) or [2-Ph2P(6-Me3Si-C6H3)S]Ni[Me3Si(PMe3)C-CHPh] (11), and [2-Ph2P(4-Me3Si-C6H3)S]Ni[Ph(PMe3)C-CHSiMe3] (12) or [2-Ph2P(4-Me3Si-C6H3)S]Ni[Me3Si(PMe3)C-CHPh] (12) contg. a ylidic ligand were formed by the reaction of phenylacetylene, diphenylacetylene, and 1-phenyl-2-(trimethylsilyl)acetylene with 1, 2, and 3, resp. The phenyl/vinyl exchange Ni(II) complexes [2-(PhCH2:CSiMe3)P(4-Me-C6H3)S]Ni(Ph)(PMe3) (13), [2-(PhCH2:CSiMe3)P(6-Me3Si-C6H3)S]Ni(Ph)(PMe3) (14), and [2-(PhCH2:CSiMe3)P(4-Me3Si-C6H3)S]Ni(Ph)(PMe3) (15) could be obtained by insertion of trimethylsilylacetylene into Ni-H bonds of 1, 2, and 3. This is a novel reaction type between alkyne and Ni hydride. Whether increasing the electronegativity on the benzene ring or on the alkyne leads to the instability of the vinyl Ni complex, and is beneficial to the C-P reductive elimination to form nickelacyclopropane complexes or Ph Ni complexes via vinyl/phenyl exchange reaction in the case of the more electroneg. Ni center. All the Ni complexes were fully detected by IR, NMR and the mol. structures of complexes 1, 2, 7, 9, 13, and 14 were confirmed by single crystal x-ray diffraction.
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30. 30
  An alternative pathway involving oxidative addition of ortho C(sp²)–H bond with the Ni(0) catalyst was considered computationally. The barrier of the C–H oxidative addition is 19.5 kcal/mol with respect to amide 1 and Ni(cod)₂. However, the subsequent steps in this pathway were highly disfavored. Both alkyne insertion into Ni–H bond and N–H deprotonation to form the five-membered Ni(II) metallacycle 9 require very high activation barriers of 44.5 and 67.2 kcal/mol with respect to 1 and Ni(cod)₂, respectively. Based on these results, this oxidative addition pathway was ruled out (see Supporting Information for more details).
  There is no corresponding record for this reference.
31. 31
  (a) Brookhart, M.; Green, M. L. H.; Parkin, G. Agostic interactions in transition metal compounds. Proc. Natl. Acad. Sci. USA 2007, 104, 6908– 6914, DOI: 10.1073/pnas.0610747104
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  Agostic interactions in transition metal compounds
  Brookhart, Maurice; Green, Malcolm L. H.; Parkin, Gerard
  Proceedings of the National Academy of Sciences of the United States of America (2007), 104 (17), 6908-6914CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
  A review of the impact of agostic interactions (i.e., 3-center-2-electron M-H-C bonds) on the structures and reactivity of organotransition metal compds. is presented.
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  .
  (b) Jongbloed, L. S.; García-Lopez, D.; Heck, R. V.; Siegler, M. A.; Carbo, J. J.; Vlugt, J. I. V. D. Arene C(sp2)-H Metalation at NiII Modeled with a Reactive PONCPh Ligand. Inorg. Chem. 2016, 55, 8041– 8047, DOI: 10.1021/acs.inorgchem.6b01162
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  31b
  Arene C(sp2)-H metalation at NiII modeled with a reactive PONCPh ligand
  Jongbloed, Linda S.; Garcia-Lopez, Diego; van Heck, Richard; Siegler, Maxime A.; Carbo, Jorge J.; van der Vlugt, Jarl Ivar
  Inorganic Chemistry (2016), 55 (16), 8041-8047CODEN: INOCAJ; ISSN:0020-1669. (American Chemical Society)
  Coordination of the reactive phosphinitopyridylphenyl PONCPh ligand, 6-Ph-2-tBu2PO-pyridine (HL) to NiBr2 initially yields paramagnetic brown [NiBr2(HL-κN,κP)] (1), but addn. of triethylamine results in fast and facile cyclometalation at NiII, giving [NiBr(κ3-P,N,C-L)] (2) as well-defined species. This is a rare example of direct cyclometalation at NiII from a C-H bond in a ligand structure other than encumbering ligands (e.g., ECE pincers). Diamagnetic yellow complex 2 protonates instantaneously in reaction with HBF4 to give purple [NiBr(κ3-P,N-HL)]BF4 (3). A very unusual (an)agostic Ni(CPh-H) interaction in the solid-state structure of 3 was unequivocally demonstrated using single-crystal x-ray crystallog. and was interpreted by d. functional theory calcns. (quantum theory of atoms in mols. and electron localization function anal.). These compds. may be viewed as models for key intermediates in the Ni-catalyzed C-H functionalization of arenes.
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  Characterization of agostic interactions in theory and computation
  Lein, Matthias
  Coordination Chemistry Reviews (2009), 253 (5+6), 625-634CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
  A review. Agostic interactions are covalent intramol. interactions between an electron deficient metal and a σ-bond in close geometrical proximity to the metal atom. While the classic cases involve CH σ-bonds close to early transition metals like Ti, many more agostic systems were proposed which contain CH, SiH, BH, CC, and SiC σ -bonds coordinated to a wide range of metal atoms. Recent computational studies of a multitude of agostic interactions are reviewed in this contribution. It is highlighted how several difficulties with the theor. description of the phenomenon arise because of the relative weakness of this interaction. The methodol. used to compute and interpret agostic interactions is presented and different approaches such as atoms in mols. (AIMs), natural bonding orbitals (NBOs) or the electron localization function (ELF) are compared and put into context. A brief overview of the history and terminol. of agostic interactions is given in the introduction and fundamental differences between α-, β-, and other agostic interactions are explained.
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  (d) Etienne, M.; Weller, A. S. Intramolecular C–C agostic complexes: C–C sigma interactions by another name. Chem. Soc. Rev. 2014, 43, 242– 259, DOI: 10.1039/C3CS60295H
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  Intramolecular C-C agostic complexes: C-C sigma interactions by another name
  Etienne, Michel; Weller, Andrew S.
  Chemical Society Reviews (2014), 43 (1), 242-259CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  A review of the developments in the synthesis, characterization and reactivity of complexes (s-, d- and f-block) in which a C-C single bond interacts with a metal center are discussed: so called C-C···M agostic complexes. Such species are of significant interest with regard to structure and bonding, the activation of C-C single bonds and, thus, catalytic methods of C-C bond formation (or activation). Examples of C-C agostic complexes of early and later transition metals, actinides and Group 1 metals are discussed, along with C-C agostic interactions in metallacyclobutanes. Examples of Si-Si···M, B-C···M and B-B···M agostic interactions are also presented. Throughout, the structural, spectroscopic and computational markers that indicate the likely presence of a C-C···M agostic interaction in a complex are highlighted.
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  (e) Beattie, D. D.; Bowes, E. G.; Drover, M. W.; Love, J. A.; Schafer, L. L. Oxidation State Dependent Coordination Modes: Accessing an Amidate-Supported Nickel(I) δ-bis(C–H) Agostic Complex. Angew. Chem. 2016, 128, 13484– 13489, DOI: 10.1002/ange.201607243
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  (f) Crabtree, R. H. Sigma Bonds as Ligand Donor Groups in Transition Metal Complexes. The Chemical Bond III; Mingos, D.M.P., Ed.; Springer International Publishing: Switzerland, 2015; Vol. 171, pp 63– 78.
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  An alternatively pathway to form intermediate 11 from phosphine-bound Ni(II)-hydride complex 5 via σ-bond metathesis followed by PPh₃ decomplexation requires a much higher barrier (66.0 kcal/mol with respect to aromatic amide 1 and Ni(cod)₂ catalyst). This very high barrier is due to the absence of an agostic interaction and unfavorable steric effects of the additional PPh₃ ligand.
  There is no corresponding record for this reference.
33. 33
  PPh₃ coordination to intermediate 8 forms an off-cycle phosphine-bound alkenyl-Ni(II) complex 7. Complex 7 is 11.2 kcal/mol more stable than 8.
  There is no corresponding record for this reference.
34. 34
  (a) Another mechanism for C–H metalation involves σ-bond metathesis of the Ni–N bond in intermediate 8 with the ortho C–H bond to form a five-membered alkenyl-nickelacycle (see Supporting Information for details). This process requires an activation barrier of 39 kcal/mol with respect to the separate reactants and Ni(cod)₂, and thus can be ruled out.
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  (b) In our calculations, we could not locate neither the transition state structure for the oxidative addition of the ortho C(sp²)–H bond from alkenyl-Ni(II) complex 8 nor the resulting Ni(IV)-hydride complex. All attempts to locate these structures resulted in TS3, 8, or 9. Intrinsic reaction coordinate (IRC) calculations were carried out for TS3 to confirm that it connects to complexes 8 and 9.
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35. 35
  We also computationally considered the use of cis-2-butene rather than 2-butyne as the H₂ acceptor to promote the C–H metalation. In this alternatively pathway, the barrier of σ-bond metathesis is 34.8 kcal/mol with respect to the separate reactants and Ni(cod)₂, and thus this pathway is less favorable than that using alkyne as H₂ acceptor (see Supporting Information for details).
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36. 36
  McCarren, P. R.; Liu, P.; Cheong, P. H.-Y.; Jamison, T. F.; Houk, K. N. Mechanism and Transition-State Structures for Nickel-Catalyzed Reductive Alkyne–Aldehyde Coupling Reactions. J. Am. Chem. Soc. 2009, 131, 6654– 6655, DOI: 10.1021/ja900701g
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  Mechanism and Transition-State Structures for Nickel-Catalyzed Reductive Alkyne-Aldehyde Coupling Reactions
  McCarren, P. R.; Liu, Peng; Cheong, Paul Ha-Yeon; Jamison, Timothy F.; Houk, K. N.
  Journal of the American Chemical Society (2009), 131 (19), 6654-6655CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  The mechanism of nickel-catalyzed reductive alkyne-aldehyde coupling reactions has been investigated using d. functional theory. The preferred mechanism involves oxidative cyclization to form the nickeladihydrofuran intermediate followed by transmetalation and reductive elimination. The rate- and selectivity-detg. oxidative cyclization transition state is analyzed in detail. The d → π*.perp. back-donation stabilizes the transition state and leads to higher reactivity for alkynes than alkenes. Strong Lewis acids accelerate the couplings with both alkynes and alkenes by coordinating with the aldehyde oxygen in the transition state.
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37. 37
  In addition, the N in 2-pyridinylmethylamine is a better donor that electronically promotes the reductive elimination via TS6.
  There is no corresponding record for this reference.
38. 38
  Liang, L.-C.; Pin-Shu Chien, P.-S.; Lee, P.-Y. Phosphorus and Olefin Substituent Effects on the Insertion Chemistry of Nickel(II) Hydride Complexes Containing Amido Diphosphine Ligands. Organometallics 2008, 27, 3082– 3093, DOI: 10.1021/om701294a
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  38
  Phosphorus and olefin substituent effects on the insertion chemistry of nickel(II) hydride complexes containing amido diphosphine ligands
  Liang, Lan-Chang; Chien, Pin-Shu; Lee, Pei-Ying
  Organometallics (2008), 27 (13), 3082-3093CODEN: ORGND7; ISSN:0276-7333. (American Chemical Society)
  Ni(II) hydride complexes supported by amido diphosphine ligands, including sym. [N(o-C6H4PR2)2]- ([R-PNP]-; R = Ph, iPr, Cy) and unsym. [N(o-C6H4PPh2)(o-C6H4PiPr2)]- ([Ph-PNP-iPr]-), were prepd. for the study of olefin insertion chem. The unsym. ligand precursor H[Ph-PNP-iPr] (1d) that features different substituents (Ph and isopropyl) at the two P donors was prepd. in 53% yield as colorless crystals. Treatment of Ni(COD)2 (COD = cycloocta-1,5-diene) with H[R-PNP] (R = Ph (1a), iPr (1b), Cy (1c)) or 1d produced the corresponding four-coordinate Ni hydride complexes 2a-d. Attempts to isolate 2a led instead to the cyclooct-4-en-1-yl complex [Ph-PNP]Ni(η1-C8H13) (3a) as a consequence of COD insertion into the Ni-H bond of 2a. The reactions of 2a,d with ethylene, 1-hexene, and norbornene, resp., generated cleanly the corresponding Et (4a,d), n-hexyl (5a,d), and 2-norbornyl (6a,d) complexes. The quant. formation of 5a,d is indicative of exclusive 1,2-insertion of 1-hexene. In contrast, styrene inserts into the Ni-H bond of 2d in an exclusively 2,1-manner to afford [Ph-PNP-iPr]NiCH(Me)Ph (7d) quant. The selective 2,1-insertion products [Ph-PNP]NiCH(Me)CO2Me (8a), [iPr-PNP]NiCH(Me)CO2Me (8b), [Cy-PNP]NiCH(Me)CO2Me (8c), and [Ph-PNP-iPr]NiCH(Me)CO2Me (8d) were also isolated from the reactions of Me acrylate with the corresponding Ni hydride complexes 2a-d. The effects of the P and olefin substituents on the reactivity and regioselectivity of the olefin insertion reactions are discussed. In addn. to soln. NMR spectroscopic data for all new compds., x-ray structures of 1d, 2b-d, 3a, and 5d-7d are reported.
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  (a) Kogut, E.; Zeller, A.; Warren, T. H.; Strassner, T. Structure and Dynamics of Neutral β-H Agostic Nickel Alkyls: A Combined Experimental and Theoretical Study. J. Am. Chem. Soc. 2004, 126, 11984– 11994, DOI: 10.1021/ja0477221
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  39a
  Structure and Dynamics of Neutral β-H Agostic Nickel Alkyls: A Combined Experimental and Theoretical Study
  Kogut, Elzbieta; Zeller, Alexander; Warren, Timothy H.; Strassner, Thomas
  Journal of the American Chemical Society (2004), 126 (38), 11984-11994CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Addn. of BF3·OEt2 to ethereal solns. of the Ni(II) β-diketiminates [Me2NN]Ni(R)(2,4-lutidine) (Me2NN = 2,6-Me2C6H3N:CMeCHC(Me):NC6H3Me2-2,6; R = Et (1), Pr (2)) gave the neutral β-H agostic monoalkyls [Me2NN]Ni(R) (R = Et (3), Pr (4)). X-ray studies of primary alkyls 3 and 4a reveal acute Ni-Cα-Cβ angles with short Ni-Cβ distances, indicating structures along the β-H elimination pathway. Positional disorder of the alkyl group in the x-ray structure of 4 corresponds to partial (22%) occupancy by the secondary alkyl [Me2NN]Ni(CHMe2) (4b). Variable-temp. NMR spectra of 3 and 4 reveal fluxional behavior that result from β-H elimination, in-plane rotation of the β-CH3 group, and a tetrahedral triplet structure for 3 that were studied by d. functional theory calcns. at the Becke3LYP/6-31G* level of theory without simplifications on the β-diketiminate ancillary ligand. Calcns. support low temp. NMR studies that identify the linear β-H agostic Pr isomer 4a as the ground state with the branched β-H agostic isomer 4b slightly higher in energy. NMR studies and calcns. show that the β-agostic 3 reluctantly coordinates ethene and that 3 is the ground state for this ethylene oligomerization catalyst. The thermodn. isotope effect KH/KD = 1.3(2) measured for the loss of 2,4-lutidine from 1 to form β-agostic 3 was also examd. by DFT calcns.
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  (b) Scherer, W.; Herz, V.; Brück, A.; Hauf, C.; Reiner, F.; Altmannshofer, S.; Leusser, D.; Stalke, D. The Nature of β-Agostic Bonding in Late-Transition-Metal Alkyl Complexes. Angew. Chem., Int. Ed. 2011, 50, 2845– 2849, DOI: 10.1002/anie.201006065
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  The nature of β-agostic bonding in late-transition-metal alkyl complexes
  Scherer, Wolfgang; Herz, Verena; Brueck, Andreas; Hauf, Christoph; Reiner, Florian; Altmannshofer, Sandra; Leusser, Dirk; Stalke, Dietmar
  Angewandte Chemie, International Edition (2011), 50 (12), 2845-2849, S2845/1-S2845/62CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Nickel(II) diphosphine cycloalkyl complexes [(dtbpe)NiR][BF4] [2b-d, dtbpe = 1,2-bis(di-tert-butylphosphino)ethane, R = norbornyl, dicyclopentadien-8-yl, 3,4-dihydrodicyclopentadien-8-yl], featuring increased steric bulk of the cycloalkyl group and hindered rotation of agostic β-CH fragment, were prepd. and studied by NMR spectroscopy and theor. calcns.; comparison is made with highly-fluxional Et deriv. [(dtbpe)NiEt][BF4] (2a). Proton NMR chem. shifts were calcd. for 2b-d and compared to exptl. values. Both exptl. and theor. charge d. maps reveal a stable Cβ-Hβ bond path, however, showing a significantly decreased charge d. Accordingly, the complexes 2 feature short Ni-Hβ distances (1.671 Å) with a significant electron d. accumulation at the Ni-Hβ crit. point. Both upfield and downfield shifts of the agostic proton are obsd., depending on the particular charge distribution around the nickel center and bond geometry.
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  Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, revision D.01; Gaussian, Inc.: Wallingford, CT, 2010.
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  (a) Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648– 5652, DOI: 10.1063/1.464913
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  Density-functional thermochemistry. III. The role of exact exchange
  Becke, Axel D.
  Journal of Chemical Physics (1993), 98 (7), 5648-52CODEN: JCPSA6; ISSN:0021-9606.
  Despite the remarkable thermochem. accuracy of Kohn-Sham d.-functional theories with gradient corrections for exchange-correlation, the author believes that further improvements are unlikely unless exact-exchange information is considered. Arguments to support this view are presented, and a semiempirical exchange-correlation functional (contg. local-spin-d., gradient, and exact-exchange terms) is tested for 56 atomization energies, 42 ionization potentials, 8 proton affinities, and 10 total at. energies of first- and second-row systems. This functional performs better than previous functionals with gradient corrections only, and fits expt. atomization energies with an impressively small av. abs. deviation of 2.4 kcal/mol.
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  Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density
  Lee, Chengteh; Yang, Weitao; Parr, Robert G.
  Physical Review B: Condensed Matter and Materials Physics (1988), 37 (2), 785-9CODEN: PRBMDO; ISSN:0163-1829.
  A correlation-energy formula due to R. Colle and D. Salvetti (1975), in which the correlation energy d. is expressed in terms of the electron d. and a Laplacian of the 2nd-order Hartree-Fock d. matrix, is restated as a formula involving the d. and local kinetic-energy d. On insertion of gradient expansions for the local kinetic-energy d., d.-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calcns. on a no. of atoms, pos. ions, and mols., of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent.
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  (a) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements: Two New Functionals and Systematic Testing of Four M06-Class Functionals and 12 Other Functionals. Theoretical Chemistry Accounts; Springer, 2008; Vol. 120, pp 215– 241.
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  Density Functionals with Broad Applicability in Chemistry
  Zhao, Yan; Truhlar, Donald G.
  Accounts of Chemical Research (2008), 41 (2), 157-167CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
  A review. Although d. functional theory is widely used in the computational chem. community, the most popular d. functional, B3LYP, has some serious shortcomings: (i) it is better for main-group chem. than for transition metals; (ii) it systematically underestimates reaction barrier heights; (iii) it is inaccurate for interactions dominated by medium-range correlation energy, such as van der Waals attraction, arom.-arom. stacking, and alkane isomerization energies. We have developed a variety of databases for testing and designing new d. functionals. We used these data to design new d. functionals, called M06-class (and, earlier, M05-class) functionals, for which we enforced some fundamental exact constraints such as the uniform-electron-gas limit and the absence of self-correlation energy. Our M06-class functionals depend on spin-up and spin-down electron densities (i.e., spin densities), spin d. gradients, spin kinetic energy densities, and, for nonlocal (also called hybrid) functionals, Hartree-Fock exchange. We have developed four new functionals that overcome the above-mentioned difficulties: (a) M06, a hybrid meta functional, is a functional with good accuracy "across-the-board" for transition metals, main group thermochem., medium-range correlation energy, and barrier heights; (b) M06-2X, another hybrid meta functional, is not good for transition metals but has excellent performance for main group chem., predicts accurate valence and Rydberg electronic excitation energies, and is an excellent functional for arom.-arom. stacking interactions; (c) M06-L is not as accurate as M06 for barrier heights but is the most accurate functional for transition metals and is the only local functional (no Hartree-Fock exchange) with better across-the-board av. performance than B3LYP; this is very important because only local functionals are affordable for many demanding applications on very large systems; (d) M06-HF has good performance for valence, Rydberg, and charge transfer excited states with minimal sacrifice of ground-state accuracy. In this Account, we compared the performance of the M06-class functionals and one M05-class functional (M05-2X) to that of some popular functionals for diverse databases and their performance on several difficult cases. The tests include barrier heights, conformational energy, and the trend in bond dissocn. energies of Grubbs' ruthenium catalysts for olefin metathesis. Based on these tests, we recommend (1) the M06-2X, BMK, and M05-2X functionals for main-group thermochem. and kinetics, (2) M06-2X and M06 for systems where main-group thermochem., kinetics, and noncovalent interactions are all important, (3) M06-L and M06 for transition metal thermochem., (4) M06 for problems involving multireference rearrangements or reactions where both org. and transition-metal bonds are formed or broken, (5) M06-2X, M05-2X, M06-HF, M06, and M06-L for the study of noncovalent interactions, (6) M06-HF when the use of full Hartree-Fock exchange is important, for example, to avoid the error of self-interaction at long-range, (7) M06-L when a local functional is required, because a local functional has much lower cost for large systems.
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  Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. Universal Solvation Model Based on Solute Electron Density and on a Continuum Model of the Solvent Defined by the Bulk Dielectric Constant and Atomic Surface Tensions. J. Phys. Chem. B 2009, 113, 6378– 6396, DOI: 10.1021/jp810292n
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  Universal Solvation Model Based on Solute Electron Density and on a Continuum Model of the Solvent Defined by the Bulk Dielectric Constant and Atomic Surface Tensions
  Marenich, Aleksandr V.; Cramer, Christopher J.; Truhlar, Donald G.
  Journal of Physical Chemistry B (2009), 113 (18), 6378-6396CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)
  We present a new continuum solvation model based on the quantum mech. charge d. of a solute mol. interacting with a continuum description of the solvent. The model is called SMD, where the "D" stands for "d." to denote that the full solute electron d. is used without defining partial at. charges. "Continuum" denotes that the solvent is not represented explicitly but rather as a dielec. medium with surface tension at the solute-solvent boundary. SMD is a universal solvation model, where "universal" denotes its applicability to any charged or uncharged solute in any solvent or liq. medium for which a few key descriptors are known (in particular, dielec. const., refractive index, bulk surface tension, and acidity and basicity parameters). The model separates the observable solvation free energy into two main components. The first component is the bulk electrostatic contribution arising from a self-consistent reaction field treatment that involves the soln. of the nonhomogeneous Poisson equation for electrostatics in terms of the integral-equation-formalism polarizable continuum model (IEF-PCM). The cavities for the bulk electrostatic calcn. are defined by superpositions of nuclear-centered spheres. The second component is called the cavity-dispersion-solvent-structure term and is the contribution arising from short-range interactions between the solute and solvent mols. in the first solvation shell. This contribution is a sum of terms that are proportional (with geometry-dependent proportionality consts. called at. surface tensions) to the solvent-accessible surface areas of the individual atoms of the solute. The SMD model has been parametrized with a training set of 2821 solvation data including 112 aq. ionic solvation free energies, 220 solvation free energies for 166 ions in acetonitrile, methanol, and DMSO, 2346 solvation free energies for 318 neutral solutes in 91 solvents (90 nonaq. org. solvents and water), and 143 transfer free energies for 93 neutral solutes between water and 15 org. solvents. The elements present in the solutes are H, C, N, O, F, Si, P, S, Cl, and Br. The SMD model employs a single set of parameters (intrinsic at. Coulomb radii and at. surface tension coeffs.) optimized over six electronic structure methods: M05-2X/MIDI!6D, M05-2X/6-31G*, M05-2X/6-31+G**, M05-2X/cc-pVTZ, B3LYP/6-31G*, and HF/6-31G*. Although the SMD model has been parametrized using the IEF-PCM protocol for bulk electrostatics, it may also be employed with other algorithms for solving the nonhomogeneous Poisson equation for continuum solvation calcns. in which the solute is represented by its electron d. in real space. This includes, for example, the conductor-like screening algorithm. With the 6-31G* basis set, the SMD model achieves mean unsigned errors of 0.6-1.0 kcal/mol in the solvation free energies of tested neutrals and mean unsigned errors of 4 kcal/mol on av. for ions with either Gaussian03 or GAMESS.
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsomega.9b00030.
- Reaction energy profiles of amide N–H oxidative addition with different ligands (Figure S1), alternative C−H metalation mechanisms with cis-2-butene (Figure S2), via σ-bond metathesis of phosphine-bound Ni(II)-hydride (Figure S3), via oxidative addition to Ni(0) (Figure S4), via deprotonation by the amide N (Figure S5), and C−N reductive elimination with model substrates (Figure S6); Cartesian coordinates of optimized geometries (PDF)
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Computational Study of the Ni-Catalyzed C–H Oxidative Cycloaddition of Aromatic Amides with Alkynes

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Abstract

1. Introduction

Scheme 1

Scheme 2

2. Results and Discussion

2.1. Proposed Reaction Mechanisms

Scheme 3

2.2. Mechanisms of the Ortho C(sp2)–H Metalation Step and the Role of Alkyne as a Hydrogen Acceptor

Figure 1

2.3. Mechanisms of Ni–C Insertion and C–N Bond Formation Steps and the Effects of Phosphine Additives and the 2-Pyridinylmethylamine Directing Group

Figure 2

Figure 3

2.4. Origin of Regioselectivity with Unsymmetrical Internal Aryl Alkynes

Scheme 4

Figure 4

2.5. Mechanism of Cis–Trans Isomerization of the Alkene Byproduct

Figure 5

3. Conclusions

4. Computational Methods

Supporting Information

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Acknowledgments

References

Cited By

Abstract

Scheme 1

Scheme 2

Scheme 3

Figure 1

Figure 2

Figure 3

Scheme 4

Figure 4

Figure 5

References

Supporting Information

Supporting Information

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2.2. Mechanisms of the Ortho C(sp²)–H Metalation Step and the Role of Alkyne as a Hydrogen Acceptor