Synthesis and Characterization of Pincer-Molybdenum Precatalysts for CO2 Hydrogenation

A family of low-valent molybdenum complexes supported by the pincer ligand PNMeP (PNMeP = MeN­(CH2CH2PPh2)2) was prepared and characterized, including (PNMeP)­Mo­(C2H4)2, which contains an agostic interaction between the metal and the N-methyl substituent. This β-agostic C–H bond was cleaved by molybdenum and produced a cyclometalated molybdenum formate complex, (κ4-PNMeP)­Mo­(C2H4)­(κ2-O2CH), upon exposure to CO2. This species serves as a promotor of CO2 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.