Tetravalent Metal Complexes as a New Family of Catalysts for Copolymerization of Epoxides with Carbon Dioxide

New tetravalent metal complexes with a trianionic [ONNO]-tetradentate ligand and an ancillary chloride ligand were synthesized as catalysts for the copolymerization of epoxides with carbon dioxide (CO2). All of the titanium, zirconium, germanium, and tin complexes were found to copolymerize epoxides with CO2. In particular, the copolymerization of propylene oxide with CO2 gave the almost-completely alternating copolymers by using titanium or germanium complexes. These results are the first example of the copolymerization using tetravalent metal complexes as a main component of catalysts.