Homogenous dual-ligand zinc complex catalysts for chemical fixation of CO₂ to propylene carbonate

Homogeneous dual-ligand zinc complex catalysts was developed for the synthesis of propylene carbonate (PC) through chemical fixation of CO₂. It was found that among a number of various pK_a N-donor ligands, the catalytic performance was enhanced dramatically and the corrosion of the reaction system was effectively inhibited when 1-methylimidazol (1MI) was used as the N-donor ligand, in which>90 % PC yield could be obtained under mild reaction conditions. The dual-ligand zinc complex catalysts were characterized by various spectroscopic techniques such as FT-IR and ¹HNMR. X-ray crystallography showed that the Zn(II) atom was coordinated in tetrahedron geometry by three bromine atom, one 1MI nitrogen atom, and one crystallographically independent cation to give a 3D tetrahedron structure, which forms tetracoordinated complexes. The structure of the complex gives the reasons for the enhancement of the catalytic activity from the microscopic molecular structure point of an extremely long and therefore labile Zn-Br bond, the diversification of the bond angles, and the interplay between the steric hindrance, which have great influence on the interaction forces of Zn-Br.