Theoretical Investigation on Nickel-Catalyzed Hydrocarboxylation of Alkynes Employing Formic Acid

Abstract

DFT calculations have been conducted to elucidate the mechanistic details of a novel Ni-catalyzed hydrocarboxylation reaction of alkynes, in which formic acid is atom-economically used through a catalytic CO recycling manner. On the basis of our theoretical investigations, the bisphosphine (dppbz, 1,2-bis(diphenylphosphino)benzene) ligated nickel monocarbonyl complex (dppbz)NiCO was located as the active catalytic species for this process, and such a carbonyl ligand is found to be critical for the final reductive elimination. Our studies also revealed the addition of H to alkynes proceeds via a proton transfer process directly from formic acid (i.e., outer-sphere pathway) rather than through a proposed hydrometalation process (i.e., direct hydride shift from Ni–H). The thermal decomposition of formic anhydrides was found to be vital to a successful reaction, and its barrier must be slightly higher than the energetic span of the Ni catalytic cycle. Fast release of CO can poison the Ni catalyst, so that the...