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

• New Cr(III) complexes with tridentate base Schiff NN′O-donor have been prepared.
• These complexes with a co-catalyst are active catalysts in the coupling of CO2/epoxides.
• Up to 900 g of polycarbonate/g Cr was obtained from cyclohexene oxide/CO2.
• A conversion up to 97% in cyclic carbonate was obtained from styrene oxide/CO2.

New Cr(III) hexacoordinated complexes with tridentate NN′O-donor Schiff base ligands, M(NN′O)2Cl, 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 oxide reacts 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 oxides form 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.

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