Merling, Everett
(2015)
Synthesis and Reactions of Heterosubstituted N-Heterocyclic Carbene-Boranes.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Carbene-boranes 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene borane (dipp-Imd-BH3) and 1,3-dimethylimidazol-2-ylidene borane (diMe-Imd-BH3) were treated with various electrophiles to compare reactivity of carbene-borane with nucleophilicity values of carbene-borane (dipp-Imd-BH3 = 9.55 N, diMe-Imd-BH3 = 11.88 N). Compounds with electrophilicity values greater –15 E reacted rapidly with carbene-borane, but compounds with electrophilicity values less than –15 E reacted slowly or not at all with carbene-borane. Hydroboration complexes were isolated from the reactions of diMe-Imd-BH3 with benzylidenemalononitrile and 2-ethylidenemalononitrile. Overall the reactivity of carbene-borane matched predictions based on nucleophilicity and electrophilicity values.
Carbene-boranes were also treated with acid halides and halogens to form halogenated carbene-boranes. Iodination occurs most rapidly followed by bromination and then chlorination. Dipp-Imd-BH3 can only be iodinated once likely due to the steric bulk around the boron atom while diMe-Imd-BH3 can be iodinated once (0.5 equiv of I2 added) or twice (1.0 equiv of I2 added). Tribromination and trichlorination was possible for both carbene-boranes. Disproportionation of the halides bonded to the boron atoms occurred rapidly with iodide and slowly with bromide. These halogenated carbene-boranes also were reduced by lithium aluminum deuteride to give selectively deuterated carbene-borane species, and also underwent nucleophilic substitutions to give carbene-boryl-azide.
[3+2]-Dipolar cycloaddition reactions were performed on carbene-boryl-azide with electron deficient alkynes, alkenes, and nitriles to give new carbene-boryl-triazoles, -triazolidines, and -tetrazoles. Electron deficient alkynes and alkenes such as propiolate and acrylate were reactive with carbene-boryl-azide even at room temperature, but less electron deficient alkynes, nitriles, and alkenes required heating or microwave radiation to form cycloaddition borane products.
Carbene-boryl-triazoles are very robust and can withstand reductive and acidic conditions. The triazole can even be methylated by methyl iodide or methyl triflate to give a carbene-boryl-triazole salt. The triazole could be detached from the boron atom by reacting the boron atom with halogen, and decomplexing the carbene-borane in methanol.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
27 September 2015 |
| Date Type: |
Publication |
| Defense Date: |
10 April 2015 |
| Approval Date: |
27 September 2015 |
| Submission Date: |
16 April 2015 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
149 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Chemistry |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
carbene borane azide dipolar cycloaddition triazole triazolidines tetrazole nucleophilicity electrophilicity |
| Date Deposited: |
27 Sep 2015 22:29 |
| Last Modified: |
15 Nov 2016 14:27 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/24858 |
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