Barnett C, Cole ML, Harper JB. The Core Difference between a Mesoionic and a Normal
N-Heterocyclic Carbene.
ACS OMEGA 2022;
7:34657-34664. [PMID:
36188285 PMCID:
PMC9520694 DOI:
10.1021/acsomega.2c04682]
[Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/25/2022] [Accepted: 08/23/2022] [Indexed: 06/16/2023]
Abstract
The properties of the abnormal N-heterocyclic carbene (NHC) 1,4-dimesityl-3-methyl-1,2,3-triazolin-5-ylidene were comprehensively compared to those of the related normal carbene 1,3-dimesitylimidazolin-2-ylidene using a range of steric and electronic probe techniques (% V bur, steric maps, Tolman electronic parameter, alane, Huynh electronic parameter, selone, and pK a values). The two NHCs were determined to be sterically equivalent (isostructural), while the triazolin-5-ylidene was found to be a stronger σ-electron donor and a much weaker π-electron acceptor. These results were used to demonstrate that the electronic properties of these NHCs could affect the stereochemical outcome of an NHC-catalyzed reaction.
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