Synthesis and Characterization of Pincer-Molybdenum Precatalysts for CO2 Hydrogenation

A family of low-valent molybdenum complexes supported by the pincer ligand (PNP)-P-Me ((PNP)-P-Me = MeN(CH2CH2PPh2)(2)) was prepared and characterized, including ((PNP)-P-Me)Mo(C2H4)(2), which contains an agostic interaction between the metal and the N-methyl substituent. This beta-agostic C-H bond was cleaved by molybdenum and produced a cyclometalated molybdenum formate complex, (kappa(4)-(PNP)-P-Me)-Mo(C2H4)(kappa(2)-O2CH), upon exposure to CO2. This species serves as a promotor of CO, hydrogenation to formate under basic conditions, a rare transformation for group VI metals. The performance of the precatalyst was enhanced with the addition of Lewis acid salts.