A Missing Piece of the Mechanism in Metal-Catalyzed Hydrogenation: Co(-I)/Co(0)/Co(+I) Catalytic Cycle for Co(-I)-Catalyzed Hydrogenation.

Hydrogenation catalyzed by unusually low-valent Co(-I) and Fe(-I) catalysts were recently reported. In contrast to the classical M(I)/M(III) (M = Rh or Ir) or Ir(III)/Ir(V) catalytic cycles in the singlet state (adiabatic reactions) for Rh- or Ir-catalyzed hydrogenation, our systematic DFT study elucidates a new Co(-I)/Co(0)/Co(+I) catalytic cycle involving both singlet and triplet states (nonadiabatic reaction). Also, the more electron-rich cobalt center of the Co(-I) catalyst was found to contribute higher reactivity for alkene hydrogenation.