Hydrogenation Of Ethylene Carbonate Catalyzed By N-Heterocyclic Carbene Ligands And Ruthenium Precursors

CO2 is the main greenhouse gas and the increasing amount of CO2 in the atmosphere has resulted in a series of environment problems. Nevertheless, CO2 is an important chemical material, which can be used to synthesize a variety of chemicals. Accordingly, reducing CO2 emissions and transforming it to chemicals would be a great challenge for governments, academia and industries. Methanol is one of the most important chemical materials and high-energy fuel, which could be synthesized by the direct hydrogenation of CO2. However, CO2 is a thermodynamically stable compound and this hydrogenation process needs harsh conditions such as high temperature and pressure. Recently, the hydrogenation of CO2 derivatives has attracted particular attentions. This not only provides an alternative approach for the indirect transformation of CO2 to methanol fuel, but also opens up a new method for the utilization of CO2. This dissertation investigates the hydrogenation of ethylene carbonate to glycol and methanol and mainly includes the following three chapters:1. A concise introduction of hydrogenation of CO2 derivatives and the application of ruthenium complexes in activation of C=O bonds.2. A series of facile and stable NHC ligands L1-L10 and Ru-NHC pincer complexes have been synthesized. Both the structures of NHC ligands and complexes were characterized by NMR spectra, FT-IR spectra, HRMS and MALDI-TOF Mass. In addition, the NMR and FT-IR spectra of NHC ligands and complexes have been comprehensively analyzed to determine the structure of the Ru-NHC complexes.3. With respect to the strong electron-donating abilities, NHC ligands L1-L10 combined with ruthenium precursors were applied as catalyst for the hydrogenation of ethylene carbonate. The influences of NHC ligands, ruthenium precursors, the type and quantity of bases, the reaction temperature, H2 pressure and reaction time on the reaction have been systemically investigated. It showed that the optimum reaction conditions are as follows:2 mol% NHC ligand L1,2 mol% RuHCl(CO)(PPh3)3, 10 mol% KO’Bu,130℃,5 MPa H2,12 h, ethylene carbonate hydrogenation obtained the highest catalytic activity with 99% conversion and the yields of methanol and glycol reached 42% and 92%, respectively. Accordingly, five metal-NHC complexes were also applied as catalysts for this reaction. All the Ru-NHC complexes presented excellent catalytic efficiencies with full conversion of ethylene carbonate, high yield of glycol (>90%) and moderate yield of methanol (>42%).