Carbon Dioxide/Epoxide Reactions Catalyzed by Bimetallic Salalen Aluminum Complexes

Four new bimetallic aluminum complexes that bear salalen ligands were synthesized and characterized. They were employed as catalysts in the reaction of CO2 with both cyclohexene oxide and propylene oxide with tetrabutyl ammonium bromide as the cocatalyst. The effect of the reaction conditions on the productivity and selectivity of the catalytic system was evaluated. Under the optimized reaction conditions, cis-cyclohexene carbonate and propylene carbonate were obtained as exclusive products, respectively. Interestingly, in the production of cis-cyclohexene carbonate, turnover frequencies comparable to those of the most active systems described in the literature were obtained. Moreover the catalytic system was active even if it was operated at a low CO2 pressure (0.2 MPa) and with a low catalyst loading (0.04 mol%).