Efficient Homogeneous Catalysis in the Reduction of CO₂ to CO

The well-defined copper(I) boryl complex [(IPr)Cu(Bpin)] [where IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, and pin = pinacolate: 2,3-dimethyl-2,3-butanediolate] deoxygenates CO2 rapidly and quantitatively, affording CO and the borate complex [(IPr)Cu(OBpin)]. The boryl may be regenerated by treatment with the diboron compound pinB-Bpin, giving the stable byproduct pinB-O-Bpin. The use of a copper(I) alkoxide precatalyst and stoichiometric diboron reagent results in catalytic reduction of CO2, with high turnover numbers (1000 per Cu) and frequencies (100 per Cu in 1 h) depending on supporting ligand and reaction conditions.