An alternative non-redox Ni(I) pathway in hydroaminomethylation: A theoretical perspective

Abstract

Herein, we report a theoretical investigation on the nickel-catalyzed hydroaminomethylation reaction of alkyne with imine. In this work, an alternative Ni(I) mechanism, without a redox reaction, was proposed by DFT calculations. The mechanism based on these calculations is favorable compared with the previously proposed redox Ni(0)-Ni(II) pathway. A Ni(I)-amino complex is considered to be the active species, which can be obtained from hydrogen transfer between an imine-coordinated Ni(0) complex and an amine. A Meerwein-Ponndorf type hydride transfer takes place between an amino group and a coordinated alkyne. Then an imine insertion affords Ni(I)-allylamino. Proton transfer with the approaching imine yields the hydroaminomethylation product and regenerates the Ni(I)-amino active species. Throughout the catalytic cycle, the oxidative state of Ni remains at +1. Furthermore, AIM analysis shows that the dissociation of the amine ligand to provide a vacancy would lead to a higher free-energy barrier for the Ni(0)-Ni(II) pathway.