Chiral Titanium(Iv) And Vanadium(V) Salen Complexes As Catalysts For Carbon Dioxide And Epoxide Coupling Reactions

Chiral titanium(IV) and vanadium(V) salen complexes were found to catalyse the synthesis of cyclic carbonates from carbon dioxide and epoxides. Reactions could be conducted at room temperature and 50 bar pressure of carbon dioxide or at 100 degrees C and atmospheric pressure with catalyst concentrations as low as 0.1 mol% and co-catalyst (tetrabutylammonium bromide) concentrations as low as 0.5 mol%. The cyclic carbonates formed were racemic and a mechanism is proposed which relies on Lewis base catalysis to activate the carbon dioxide rather than Lewis acid catalysed activation of the epoxide as more commonly proposed for catalysis by metal complexes. (C) 2021 Elsevier Ltd. All rights reserved.