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

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 alpha-methyl cyano ester and cyclic beta-keto ester substrates with various activated olefins as catalyzed by a chiral nickel N-heterocyclic carbene complex namely, {[(1-R-1-3-R-2-acetamido) imidazol-2-ylidene][(1-R-1-3-R-2-acetamidato)imidazol-2-ylidene]}NiOH [R-1 = (1S, 2S, 5R)-menthyl, R-2 = 2,6-i-Pr2C6H3 (3)] have been detected by Electrospray Ionization Mass Spectrometry (ESI-MS). (C) 2017 Elsevier B.V. All rights reserved.