The Core Difference between a Mesoionic and a Normal N-Heterocyclic Carbene

Christopher Barnett; Marcus L Cole; Jason B Harper

doi:10.1021/acsomega.2c04682

The Core Difference between a Mesoionic and a Normal N-Heterocyclic Carbene

ACS Omega. 2022 Sep 16;7(38):34657-34664. doi: 10.1021/acsomega.2c04682. eCollection 2022 Sep 27.

Authors

Christopher Barnett^{1

2}, Marcus L Cole¹, Jason B Harper¹

Affiliations

¹ School of Chemistry, The University of New South Wales, Sydney 2052, Australia.
² School of Chemistry, The University of Sydney, Sydney 2006, Australia.

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.