Mechanistic Insights into the Directed Hydrogenation of Hydroxylated Alkene Catalyzed by Bis(phosphine)cobalt Dialkyl Complexes.

The mechanism of directed hydrogenation of hydroxylated alkene catalyzed by bis(phosphine)cobalt dialkyl complexes has been studied by DFT calculations. The possible reaction channels of alkene hydrogenation catalyzed by catalytic species (0T, 0P, and 0) were investigated. The calculated results indicate that the preferred catalytic activation processes undergo a 1,2 alkene insertion. 0P and 0 prefer the β hydrogen elimination mechanism with an energy barrier of 9.5 kcal/mol, and 0T prefers the reductive elimination mechanism with an energy barrier of 11.0 kcal/mol. The second H2 coordination in the σ bond metathesis mechanism needs to break the agostic H2-βC bond of metal-alkyl intermediates (21P and 21T), which owns the larger energetic span compared to the reductive elimination. This theoretical study shows that the most favorable reaction pathway of alkene hydrogenation is the β hydrogen elimination pathway catalyzed by the planar (dppe)CoH2. The hydrogenation activity of Co(II) compounds with redox-innocent phosphine donors involves the Co(0)-Co(II) catalytic mechanism.