Alternating Copolymerization of CO2 and Cyclohexene Oxide by New Pyridylamidozinc(II) Catalysts

Five new Zn(II) complexes bearing pyridylamido ligands with different substituents at the pyridine and at the amido moieties were synthesized and evaluated as catalysts for the alternating copolymerization of carbon dioxide and cyclohexene oxide. Polymers with carbonate linkages ranging between 86 and 99% and a slightly isotactic-enriched structure were selectively obtained under a variety of reaction conditions, including 1 atm of CO2 pressure, without any cocatalyst. Some experimental and theoretical evidence suggested that different initiating species are involved in the catalytic cycle, including dimeric [(Lx)Zn(μ-OR)]2 and [(Lx)Zn(μ-O2COR)] complexes similar to those involved in the classical β-diiminate Zn(II) catalysts.