Zinc complexes with 1,2-disubstituted benzimidazole ligands: experimental and theoretical studies in the catalytic cycloaddition of CO2 with epoxides

Abstract

The synthesis and characterization of four zinc(II) complexes with monodentate 1,2-disubstituted benzimidazole ligands and their catalytic activity in the cycloaddition of CO2 and epoxides are reported. The complexes were characterized by 1H and 13C NMR, thermal analysis, infrared absorption and FT-Raman spectroscopy and ESI-HRMS. Complex Zn3 had its structure determined by single-crystal X-ray diffraction and a description of intra- and intermolecular interactions has been done. All complexes were able to catalyze the production of cyclic carbonates selectively, and complex Zn1 was used in the transformation of various epoxides to carbonates, using tetrabutylammonium bromide as cocatalyst. Quantum chemistry approaches were used to comprehend the initial step of catalytic cycle: the epoxide coordination to the metallic center. The calculations show that one benzimidazole ligand should be dislocated from the metal center before the catalyst interacts with the epoxide to activate it.