Computational insight into a gold(I) N-heterocyclic carbene mediated alkyne hydroamination reaction

A gold(I) N-heterocyclic carbene (NHC) complex mediated hydroamination of an alkyne has been modeled using density functional theory (DFT) study. In this regard, alkyne and amine coordination pathways have been investigated for the hydroamination reaction between two representative substrates, namely, MeC≡CH and PhNH(2), catalyzed by a gold(I) NHC based (NHC)AuCl-type precatalyst, namely, [1,3-dimethylimidazol-2-ylidene]gold chloride. The amine coordination pathway displayed a lower activation barrier than the alkyne coordination pathway. The catalytic cycle is proposed to proceed via a crucial proton-transfer step occurring between the intermediates [(NHC)AuCH═CMeNH(2)Ph](+) (D) and [(NHC)Au(PhNHMeC═CH(2))](+) (E), the activation barrier of which was found to be significantly reduced by a proton relay mechanism process assisted by the presence of any adventitious H(2)O molecule or even by any of the reacting PhNH(2) substrates. The final hydroaminated enamine product, PhNHMeC═CH(2), was further seen to be stabilized in its tautomeric imine form PhN═CMe(2).