Synthesis of pyrrole-based zinc complexes and their use as Lewis acid catalysts

The insertion of CO2 into epoxides requires the cooperation between a Lewis acid catalyst and a Lewis base catalyst1, usually a quaternary ammonium halide. The study of this reaction has focused on the development of new Lewis acid catalysts, among which salen complexes2 and metalloporphyrins3 are the most representative. Nitrogen Schiff base complexes (N-SB)4,5,6, that combines the properties of salens (flexibility) and porphyrins (full-nitrogen coordinating sphere), feature a new class of complexes with promising perspectives in the cycloaddition of CO2 over epoxides. Pyrrole-based Schiff Base zinc complexes (Zn-N-SB) have been synthesized using pentadentate and tetradentate ligands and fully characterized using conventional techniques (NMR, IR, XRD). Depending on the nature of the ligand, monomeric or dimeric species are obtained, showing unexpected geometries. In addition to their synthesis and characterization, the present communications will report their use as Lewis acids, along with tetrabutylammonium halides as Lewis bases, in the synthesis of styrene cyclic carbonate from CO2, affording yields up to 90%.