Are N-heterocyclic carbene radical cations relevant intermediates in radical transformations?

Abstract

N-Heterocyclic carbene (NHC) radical cations have been increasingly hypothesized as key intermediates in NHC-promoted radical reactions, but have eluded direct observation so far. Herein, we report joint experimental and theoretical efforts to assess the issues surrounding the possible existence, generation and observation of these postulated species. We show that they are unlikely to be the relevant intermediates in most NHC-promoted radical reactions.