N-heterocyclic carbene-pyridine ligand coordinated Mo(II) complexes catalyzed synthesis of cyclic carbonates from carbon dioxide and epoxides

Abstract

A variety of zero-valent molybdenum complexes and divalent molybdenum complexes with N-heterocyclic carbenes (NHC)-pyridine ligands were synthesized, and their catalytic activities and performances in the cycloaddition reaction of epoxides and carbon dioxide (CO2) were investigated. It was found that the divalent molybdenum complexes show high catalytic activity in the synthesis of cyclic carbonates from epoxide and CO2 in comparison with zero-valent molybdenum complexes. The divalent molybdenum complexes combined with tetrabutylammonium iodide (TBAI) can effectively transform various terminal epoxides and internal epoxides under 30–80 ℃ and 5–10 bar of CO2 pressure. The mechanic experiments by FT-IR and HRMS spectrometry reveal the reaction pathway of binary system in combination of divalent molybdenum complexes with TBAI.