Mass spectrometric support for a bifunctional catalysis mechanism for the base-free Michael addition by a nickel N-heterocyclic carbene complex: Detection of the catalytic intermediates

Abstract

A bifunctional catalysis mechanism for an asymmetric base-free Michael addition reaction mediated by a chiral nickel N-heterocyclic carbene complex has been corroborated by mass spectrometry. In particular, for the first time, all of the intermediates for a proposed catalytic cycle for an asymmetric base-free Michael addition of α-methyl cyano ester and cyclic β-keto ester substrates with various activated olefins as catalyzed by a chiral nickel N-heterocyclic carbene complex namely, {[(1-R1-3-R2-acetamido)imidazol-2-ylidene][(1-R1-3-R2-acetamidato)imidazol-2-ylidene]}NiOH [R1=(1S,2S,5R)-menthyl, R2=2,6-i-Pr2C6H3 (3)] have been detected by Electrospray Ionization Mass Spectrometry (ESI-MS).