The Design And Synthesis Of Bifunctional Schiff Base Metal Catalysts For The Coupling Reaction Of CO₂ And Epoxides

Carbon dioxide（CO₂）is an abundant and widespread carbon resource on the planet,which is also a main greenhouse gas that greatly affects the survival environment of human being.Meanwhile,CO₂ has played an important role in many ways to benefit human society because of its unique physical and chemical properties,such as food,firefighting,chemical industry,medicine and so on.Therefore,the chemical fixation of CO₂ is an effective method for both environmental protection and rational utilization of carbon resource.Bifunctional catalysts can promote the catalytic reaction effectively in the cycloadditon of CO₂ and epoxides for its synergistic effect of both lewis acid center and lewis base center in a molecule.In this work,two series of metal schiff-base complexes,quaternary phosphonium system and quaternary ammonium system,were synthesised and characterised（1H NMR,13 C NMR,FT-IR,elemental analysis etc.）and employed for the cycloaddition reaction.Both two catalyst systems showed high activity in the coupling reaction of CO₂ and PO to synthesis PC with high yield（96.3% and 98.6%,respectively）and good selectivity（>99%）under conditions of（140 oC、1 MPa、4 h、1 mol%;120 oC、1 MPa、3 h、1 mol%,respectively）without cocatalysts and solvents.In addition,the two catalyst systems were also demonstrated to be applicable to other epoxides.Based on the experiments and literatures a possible mechanism was proposed.We also synthesized a series of imidazolium functionalized schiff-base metal complexes on account of ionic liquid’s unique property.Imidazolium functionalized schiff-base metal complexes revealed excellent catalytic activity for the CO₂ conversion,and the effect of many reaction parameters were discussed.Comparing with former two bifunctional catalytical systems,imidazolium functionalized catalytic system demonstrated higher activity（yield: 99.2%）and selectivity（selectivity: >99%）under the conditions of（120 oC、1 MPa、2 h、1 mol%）for the coupling reaction of PO and CO₂ to generate PC.Moreover,the catalytic performance of imidazolium functionalized schiff-base metal catalysts in atmospheric pressure was also studied.These catalysts were also demonstrated to be applicable to other epoxides.The cyclic utilization test showed that imidazolium functionalized catalyts could be reused for 5 times without significant loss.