Catalytic reactions of epoxides and aziridines with carbon dioxide in the presence of salen-type complexes of 3d metals

Catalytic reactions of 3-membered heterocycles, such as epoxides and aziridines, with CO2 in the presence of metal–salen complexes are considered in this review (salens is a class of ligands, derived from diamines and salicylaldehyde or its substituted analogs). These reactions lead to copolymers or cyclic carbonates/oxazolidinones, which are important products of modern fine and industrial organic synthesis. The influence of metal ion, substituents in salen and the nature of cocatalyst on the catalytic performance of the systems based on metal–salen complexes, reported during two recent decades, is analyzed. It was shown that formation of bi- or polynuclear complexes, as well as incorporation of the organic cocatalyst (such as tetraalkylammonium cation) in the molecule of the metal-containing catalyst improved the catalytic performance of metal–salen species due to cooperative effect on several active sites in activation of epoxide and its reaction with CO2. The ways for creation of heterogeneous metal–salen catalysts for reactions of 3-membered heterocycles with CO2 are also summarized.