Synthesis and Characterization of Pincer-Molybdenum Precatalysts for CO₂ Hydrogenation

A family of low-valent molybdenum complexes supported by the pincer ligand PN^MeP (PN^MeP = MeN­(CH₂CH₂PPh₂)₂) was prepared and characterized, including (PN^MeP)­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-PN^MeP)­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.