Design And Synthesis Of Bifunctional Salen Fe Catalysts For The Coupling Reaction Of Carbon Dioxide And Epoxides

As carbon dioxide is the main greenhouse gas, but also a kind of widespread, abundant C1 feedstock on the earth. Therefore, much attention is focused on the development and utilization of carbon dioxide. The cycloaddition reaction of CO₂ and epoxides to yield cyclic carbonates is a significative reaction. The product, cyclic carbonate has been widely used in many fields, including electrolytes in lithium secondary batteries, excellent aprotic polar solvents, precursors for synthesizing polycarbonates and polyurethanes and so on. Meanwhile, the cycloaddition reaction is conformable to the notion of atom economy and green chemistry, as well as to be effective and environmentally benign, and has a huge potential in industrial application.In this paper, a series of bifunctional salen Fe complexes were synthesized as catalysts for the coupling reaction of CO₂ and propylene oxides. The influences of catalysts' structures and reaction parameters?temperature, pressure, time? on the coupling reaction were systematically investigated. After that, the stability of the catalysts had been studied. Finally, the possible reaction mechanism was also proposed. Some general conclusions were made as follows.?1? The salenFe catalysts grafted with phosphonium salt or ammonium salt weresynthesized as catalysts for the coupling reaction of CO₂ and epoxides. Thehigh yield of cyclic carbonates could be obtained even at 70 oC. The optimalconditions were 70 oC, 3MPa, 5h, PO: catalyst 2a=100:1.?2? The salenFe catalysts grafted with imidazole based ionic liquid weresynthesized as catalysts for the coupling reaction of CO₂ and epoxides. Theoptimal conditions were 120 oC, 3MPa, 3h, catalyst 2m: 0.4mol%. And the100% yield of PC was obtained.?3? Higher temperature was required when salenFe catalysts grafted withimidazole based ionic liquid were as catalysts for the coupling reaction ofCO₂ and epoxides. But it could catalyze the cycloaddition reaction of CO₂and isopropyl glycidyl ether under 1 atmosphere. Nearly 100% of cycliccarbonate was obtained in 13 h.