Mechanistic Investigation of the Nickel-Catalyzed Transfer Hydrocyanation of Alkynes

The implementation of HCN-free transfer hydrocyanation reactionson laboratory scales has recently been achieved by using HCN donorreagents under nickel- and Lewis acid co-catalysis. More recently,malononitrile-based HCN donor reagents were shown to undergo the C(sp(3))-CN bond activation by the nickel catalyst in theabsence of Lewis acids. However, there is a lack of detailed mechanisticunderstanding of the challenging C(sp(3))-CN bondcleavage step. In this work, in-depth kinetic and computational studiesusing alkynes as substrates were used to elucidate the overall reactionmechanism of this transfer hydrocyanation, with a particular focuson the activation of the C(sp(3))-CN bond to generatethe active H-Ni-CN transfer hydrocyanation catalyst.Comparisons of experimentally and computationally derived C-13 kinetic isotope effect data support a direct oxidative additionmechanism of the nickel catalyst into the C(sp(3))-CNbond facilitated by the coordination of the second nitrile group tothe nickel catalyst.