Copolymerization of CO2 and epoxides catalyzed by metal salen complexes

The design of efficient metal catalysts for the selective coupling of epoxides and carbon dioxide to afford completely alternating copolymers has made significant gains over the past decade. Hence, it is becoming increasingly clear that this greener route to polycarbonates has the potential to supplement or supplant current processes for the production of these important thermoplastics, which involve the condensation polymerization of diols and phosgene or organic carbonates. On the basis of the experiences in our laboratory, this Account summarizes our efforts at optimizing (salen)(CrX)-X-III catalysts for the selective formation of polycarbonates from alicyclic and aliphatic epoxides with CO2. An iterative catalyst design process is employed in which the salen ligand, initiator, cocatalyst, and reaction conditions are systematically varied, with the reaction rates and product selectivity being monitored by in situ infrared spectroscopy.