Mesoionic carbene cobalt complexes as multipurpose catalyst precursors for hydrosilylation and dihydropyrimidinone synthesis

Metalation of CH2OH-substituted triazolium salts with CoCl2 under basic conditions affords C,O-bidentate chelating carbene Co(III) complexes (3a, 3b), while analogous phenyl-substituted produce monodentate Co(II) (3c, 3d). The distinct substituent-induced properties the metal centers were demonstrated by electrochemical measurements and catalytic activities in two specific processes. showed appreciable activity reduction C=O bonds through hydrosilylation, methoxybenzene-functionalized triazolylidene complex 3a achieving a high selectivity towards aldehydes vs. ketones turnover frequencies (TOFs) up to 200 h−1. C,O-chelate systems also active catalysts Biginelli process, one-step three-component reaction for efficient dihydropyrimidinone synthesis. Optimization provides 3a, reaching TOFs 800 h−1, highest known cobalt NHC date.