Theoretical Study of Two Possible Side Reactions for Reductive Functionalization of 3d Metal-Methyl Complexes by Hydroxide Ion: Deprotonation and Metal-Methyl Bond Dissociation

A DFT study of two possible competitive reactions for reductive functionalization (RF) of metal methyl complexes ([M-II(diimine)(2)(CH3) (Cl)], M-II = V-II through Cu-II) was performed to understand the factors that lower the selectivity of C-O bond forming reactions. One of the possible side reactions is deprotonation of the methyl group, which leads to formation of a methylene complex and water. The other possible side reaction is metal methyl bond dissociation, which was assessed by calculating the bond dissociation free energies of M-CH3 bonds. Deprotonation was found to be competitive kinetically for most of the first-row transition-metal methyl complexes (except for Cr-II, Mn-II, and Cu-II) but less favorable thermodynamically in comparison to reductive functionalization for all of the studied first-row transition metals. Metal carbon bond dissociation was found to be less favorable than the RF reactions for most 3d transition-metal complexes studied. Therefore, this study suggests that Earth-abundant catalysts for alkane oxidation should focus on chromium-triad metals.