DFT Study of Functional Reduction of CO₂ with BH₃NMe₃: The Real Role of Organic Catalyst TBD

The detailed mechanism of transition metal-free-catalyzed monomethylation of 2-naphthyl acetonitrile (1a) with CO₂ in the presence of triazabicyclodecene (TBD) and BH₃NMe₃ was investigated using density functional theory. The C-methylation process proved to generate formaldehyde followed by the formation of the product via an alcohol rather than a methoxyborane intermediate. During the reaction, CO₂ is activated to form the TBD-CO adduct and BH₃NMe₃ is changed into TBD-BH (IM2) in the presence of TBD. IM2 plays a real reducing role within the system due to the unique coordination capability of the B atom. In addition to enhancing the nucleophilicity of 1a through deprotonation by BuOK, our research also indicates that the generated BuOH not only assists in proton transfer to generate an alcohol intermediate but also promotes the regeneration of TBD.