Abnormal N-Heterocyclic Carbene Promoted Suzuki−Miyaura Coupling Reaction: A Comparative Study

A C2-protected imidazolium salt that generates an abnormal N-heterocyclic carbene (NHC) was applied for the palladium-catalyzed Suzuki−Miyaura coupling reactions. The abnormal NHC precursor promoted the reactions while suppressing homocoupling of aryl boronic acid, which was observed with the corresponding normal NHC precursor. The related well-defined abnormal NHC-based palladium complexes also showed better activity than the normal NHC-based analogues, exhibiting faster reaction rates especially at the initial stage of the reaction.