Chromium complexes with tridentate NN′O Schiff base ligands as catalysts for the coupling of CO2 and epoxides

Abstract New Cr(III) hexacoordinatedcomplexes with tridentateNN′O-donor Schiff base ligands, M(NN′O) 2 Cl, have been prepared. They form active catalytic systems for the coupling of epoxides and carbon dioxide in the presence of co-catalysts. Best results were obtained with the complex with N-(2-pyridylmethyl)-3,5-di- tert -butyl-salicylaldimine ( 1 ) ligand and a co-catalyst. Cyclohexene oxidereacts with carbon dioxide in the presence of these catalysts to form mixtures of polycarbonate (PC) (productivity up to ca. 900 g PC/g Cr) and cyclic carbonate depending on the co-catalyst and conditions employed. Cyclopentene, styrene and propylene oxidesform selectively the cyclic carbonates at the conditions studied (epoxide conversion up to 97%). Although some of the co-catalysts are also active for the cycloaddition, the presence of both complex and co-catalyst has proved to be beneficial.