Formation of Value-Added Cyclic Carbonates by Coupling of Epoxides and CO2by Ruthenium Pincer Hydrazone Complexes under Atmospheric Pressure

Transforming atmospheric CO2 into industrially valuable cyclic carbonates is of great importance and one of the attractive approaches for reducing CO2 concentration in the biosphere. However, the selectivity and conversion of ruthenium catalysts for cyclic carbonate formation via CO2 insertion to epoxides are low at high pressure. Here, a series of novel ruthenium complexes supported by ONN pincer-type hydrazone ligands were successfully generated, and their potential for CO2 valorization to cyclic carbonates was investigated. NMR, Fourier transform infrared (FT-IR), mass spectrometry, elemental analysis, and single-crystal diffraction analysis further confirmed the structures of these ruthenium compounds. These compounds were utilized for the CO2/coupling reaction after thorough characterization. Fortunately, these complexes outperform the reported ruthenium catalysts with a turn-over frequency of 833 h–1 and >99% selectivity at atmospheric pressure without any assisted cocatalyst. The designed catalyst showed consistent catalytic performance over five repeating cycles.