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

• Published in: Journal of molecular catalysis. A, Chemical Chemical, 2014-03, Vol.383-384, p.143-152
• Main Authors: Iksi, Siham, Aghmiz, Ali, Rivas, Raquel, González, M. Dolores, Cuesta-Aluja, Laia, Castilla, Javier, Orejón, Arantxa, El Guemmout, Farid, Masdeu-Bultó, Anna M.
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Carbonates; Catalysis; Chromium; Tridentate Schiff bases
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2013.11.026

•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 900g 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. 900g 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.