The Ethylsulfinate Ligand:  A Highly Efficient Initiating Group for the Zinc β-Diiminate Catalyzed Copolymerization Reaction of CO2 and Epoxides

The quantitative synthesis of a series of new zinc(II) sulfinate complexes ( 4a − e ) by insertion of SO 2 into zinc−ethyl bonds of β-diiminate complexes ((ArN C(CH 3 )CH (CH 3 )CNAr)Zn(O(S O)Et); Ar = 2,6-diisopropylphenyl ( 4a ), 2,6-diethylphenyl ( 4b ), 2-ethyl-6-isopropylphenyl ( 4c ), 2,6-diphenylphenyl ( 4d ), 2,6-bis(4- tert -butylphenyl)phenyl ( 4e )) is described. X-ray structure analysis reveals a dinuclear, μ -ethylsulfinate-bridged structure for 4a in the solid state, which in solution exists in an equilibrium with the mononuclear species. The easily accessible complexes 4a − c are highly active catalysts for the alternating copolymerization of CO 2 and cyclohexene oxide, leading to products with narrow molecular weight distributions.