Synthesis Of Imidazole Ionic Liquid Functionalized Metalloporphyrins And Their Catalytic Properties In CO₂ Cycloaddition

Carbon dioxide gas is a rich source of carbon that can be produced and has abundant reserves on earth.In recent years,the use of carbon dioxide as a reactant in organic synthesis to achieve high-value utilization of carbon dioxide has attracted much attention.Among them,the reaction of carbon dioxide and epoxy compounds to form cyclic carbonate is a feasible strategy.Cyclic carbonate has a very large application prospect in the chemical industry,for example:polar aprotic solvents,electrolytes in lithium battery electrolytes,raw materials for synthetic polycarbonate,crude oil additives,etc.This reaction can only be carried out with the participation of a catalyst,and requires some harsh reaction conditions.For the cycloaddition reaction of carbon dioxide and epoxy compounds,a large number of catalysts have been developed.The high activity of metal porphyrin catalysts has obvious advantages over other catalysts,Among them,zinc porphyrin and magnesium porphyrin are one of the most used catalysts.Based on the above research background,this paper synthesized a series of novel metalloporphyrins and used it as a catalyst for the reaction of carbon dioxide and epoxy compounds.Specific research contents include:1.The free porphyrin containing imidazole at the periphery was 5,10,15,20-tetrakis（4-（imidazole）phenyl）porphyrin（H₂TIm P）reacted with three kinds of metal acetates respectively to obtain two kinds of metal porphyrin coordination Polymer Co-TIm P and Mg-TIm P and a metal porphyrin monomer Zn-TIm P.The single crystal structure of the two coordination polymers shows that in addition to the coordination of the N atom in the porphyrin ring,the metal also coordinates with the N atom of the imidazole adjacent to the periphery of the porphyrin in the axial direction and extends outward in the plane to form Dimensional MOF structure.Cycloaddition catalysis experiments of carbon dioxide and propylene oxide show that the catalytic activity of Co-TIm P and Mg-TIm P is very low,proving that the saturated coordination of metal porphyrin center metal is not conducive to the catalytic reaction.Under the same conditions,the monomer Zn-TIm P showed a high catalytic activity.The catalytic activity may be derived from the synergistic catalysis of the Lewis acidity of the central metal of Zn-TIm P and the Lewis base of the peripheral N atom of the imidazole.2.By alkylating the peripheral imidazoles（methyl and ethyl）of H₂TIm P,two free porphyrins H₂TMe Im P and H₂TEt Im P functionalized with two imidazole ionic liquids were synthesized and reacted with metal salts to obtain eight corresponding metal porphyrins Zn-TMe Im P,Mg-TMe Im P,Co-TMe Im P,Mn-TMe Im P,Zn-TEt Im P,Mg-TEt Im P,Co-TEt Im P,Mn-TEt Im P.The molecular structure of the synthesized porphyrin was characterized by HRMS,¹H NMR,¹³C NMR,FT-IR and UV-vis,which proved the correctness of the molecular structure of the synthesized compound.3.The catalytic performance of imidazole ionic liquid functionalized metal porphyrins epoxy compounds was investigated.Taking epichlorohydrin as substrate,the molar ratio of substrate to catalyst is 15000,under the reaction conditions of 120℃,6h,1MPa,Zn-TMe Im P shows the highest catalytic activity(Yield is 90.9%,selectivity is greater than 99%,TOF is 2275h^-1).Secondly,the reaction conditions were optimized by response surface methodology,and the best reaction conditions were 114℃,1.2MPa,6.7h（the substrate to catalyst molar ratio was 12000:1）,and the theoretical yield was 97.4%.The actual catalytic experiment yield is 97.6%,indicating that the experimental results are highly consistent with the theoretical simulation values.Under optimized reaction conditions,Zn-TMe Im P shows high catalytic activity for four epoxy compounds with different structures,with yields exceeding 90%and selectivities greater than 99%.Finally,using Zn-TMe Im P as the catalyst,under mild condition（0.1MPa CO₂）,with high boiling point phenyl glycidyl ether as the substrate,the molar ratio of the substrate to the catalyst is 4000.The effects of temperature on the reaction were explored at 60,80,and 100℃,the results showed that the yield of the corresponding cyclic carbonate was 94.3%,the selectivity was greater than 99%,and the TOF was 125.7 h^-1 at 80℃ for 30 h.