(Pyrazolylethyl-amine)zinc(II) carboxylate complexes as catalysts for the copolymerization of CO2 and cyclohexene oxide

Abstract

Pyrazolyl compounds 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)ethyl-amine) (L1), 2-(3,5-diphenyl-1H-pyrazol-1-yl)ethyl-amine (L2), and 2-(3-phenyl-5-(trifluoromethyl)-1H-pyrazol-1-yl)ethyl-amine (L3) were reacted with a mixture of zinc(II) acetate and 3,5-dinitrobenzoic acid to form the bidentate complexes [(2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)-ethyl-amine)-Zn(C6H5COO(NO2)2] (1), [(2-(3,5-diphenyl-1H-pyrazol-1-yl)ethyl-amine)Zn(C6H5COO(NO2)2] (2), and [(2-(5-phenyl-3-(trifluoro-methyl)-1H-pyrazol-1-yl)ethyl-amine)Zn(C6H5COO(NO2)2] (3) respectively. All three zinc complexes were tested as catalysts for the copolymerization of CO2 and cyclohexene oxide (CHO) and found active to form poly(cyclohexene carbonate) (PCHC) and cyclohexene carbonate (CCHC) at CO2 pressures as low as 1.5 MPa and under solvent-free conditions in the absence of a co-catalyst. Increase in CO2 pressure resulted in activity and showed selectivity up to 99% selectivity for the formation of the copolymer PCHC. Optimum temperature for the polymerization was 100 °C and even at this temperature selectivity towards formation of PCHC was found to be 99%. The copolymers obtained have moderate molecular weights (3860–11,500 g/mol) and polydispersity indices varying from 2.73 to 4.93.