Alturaifi, Turki
(2023)
Computational Study of the Impacts of Directing Group and Ligand Flexibility in Directed Alkene Functionalization.
Master's Thesis, University of Pittsburgh.
(Unpublished)
This is the latest version of this item.
Abstract
This computational study investigates the roles of flexible ligands and directing groups in Ni- and Pd-catalyzed alkene functionalization reactions. Many hemilabile and conformationally flexible ligands and directing groups have been employed in these catalytic transformations, where the ligands (e.g., bioxazolines and quinones) may adopt different binding modes and the chelating directing groups may have different ring-flip conformations. However, the effects of flexibility on reactivity and selectivity are still not well understood. Here, we examine the flexibility effects in three catalytic reactions, including the binding modes of quinone-type ligands in Ni-catalyzed 1,2-carbosulfenylation of unactivated alkenes, the coordination modes of bioxazoline-based ligands in Ni-catalyzed asymmetric 1,2-diarylation of unactivated alkenes, and the effectiveness of L-tert-leucine as a transient directing group (TDG) in controlling enantioselectivity in Heck-reductive hydrofunctionalization. We show that the duroquinone (DQ) ligand adopts different binding modes in different elementary steps of the Ni-catalyzed 1,2-carbosulfenylation—it binds as an X-type redox-active durosemiquinone (DSQ) radical anion to promote alkene migratory insertion with a less distorted square planar Ni(II) center, whereas it binds as an L-type ligand to promote oxidative addition at a more electron-rich Ni(I) center. We found that in different elementary steps of the catalytic cycle of the Ni-catalyzed alkene diarylation, the bioxazoline ligand can be bidentate, monodentate, or completely dissociated depending on the steric and electronic properties of the transition state. The enantioselectivity-determining step involves a square planar Ni(II) migratory insertion transition state, stabilized by non-covalent interactions with a dissociated arm of the bioxazoline ligand. Finally, we show how the rigidity of the bidentately bounded chiral amino acid TDGs, induced by their α-substituent, promote binding of the TDG and induce high levels of enantioselectivity in alkene insertion with a variety of migrating groups in the reductive-Heck hydrofunctionalization.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
| Creators | Email | Pitt Username | ORCID  |
|---|
| Alturaifi, Turki | tma53@pitt.edu | tma53@pitt.edu | |
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| ETD Committee: |
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| Date: |
6 September 2023 |
| Date Type: |
Publication |
| Defense Date: |
2 May 2023 |
| Approval Date: |
6 September 2023 |
| Submission Date: |
3 August 2023 |
| Access Restriction: |
1 year -- Restrict access to University of Pittsburgh for a period of 1 year. |
| Number of Pages: |
37 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Chemistry |
| Degree: |
MS - Master of Science |
| Thesis Type: |
Master's Thesis |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Flexibility, alkene functionalization, asymmetric catalysis |
| Date Deposited: |
07 Sep 2023 01:38 |
| Last Modified: |
06 Sep 2024 05:15 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/45271 |
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