Computational Insight Into the Hydroamination of an Activated Olefin, As Catalyzed by a 1,2,4-Triazole-Derived Nickel(II) N-Heterocyclic Carbene Complex.

Abstract

A density functional theory (DFT) investigation performed at the B3LYP/TZVP//B3LYP/6-31G(d)-LANL2DZ level of theory on the hydroamination of dimethylamine (Me2NH) on an activated olefin (namely, acrylonitrile (CH2═CHCN)), as catalyzed by a 1,2,4-triazol based nickel(II) N-heterocyclic carbene complex (namely, [1,4-dimethyl-1,2,4-triazole-5-ylidene]2 nickel dichloride) revealed that the olefin coordination pathway is favorable over the amine coordination pathway, although the initial olefin coordination step is higher in energy than the initial amine coordination step. Significantly enough, the reaction involved a crucial 1,3-proton transfer step between the resonance intermediates, i.e., the C-bound [(NHC)2Ni(CH(CN)CH2NHMe2)]+ (D) species or N-bound [(NHC)2Ni(NCCHCH2NHMe2)]+ (E) species and the intermediate [(NHC)2Ni(NCCH2CH2NMe2)]+ (F), depicting the cleavage of a N-H bond and the formation of a C-H bond facilitated by a water-assisted/amine-assisted proton shuttle. Overall, among the various pathways explored, the lowest energy pathway involved alkene coordination, followed by an amine-assisted 1,3-proton transfer step.