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.