Intramolecular synergistic catalysis of ternary active sites of imidazole Ionic-liquid polymers immobilized on nanosized CoFe2O4@polystyrene composites for CO2 cycloaddition

Abstract

The cycloaddition reaction of CO2 with epoxides is challenging, thereby requiring the development of environmentally friendly catalysts. Herein, a strategy was developed to construct a multifunctional heterogeneous magnetic catalyst (MPNPs-[ImR2NH2][ZnBr3]) of aminoethyl imidazole metal halide ionic liquids coated on nano-sized CoFe2O4@polystyrene for CO2 cycloaddition. The created catalytic system displayed the intramolecular synergy of ternary active sites (Zn2+, Br−, and –NH2), as well as coupling of catalysis and magnetic separation. In the absence of co-catalyst and solvent, MPNPs-[ImR2NH2][ZnBr3] exhibited excellent catalytic performance for CO2 cycloaddition (99.92% yield and 100% selectivity) at 120 ℃ with 0.16 mol% catalyst dosage in 2.5 h. By appropriately increasing the reaction duration and catalyst dosage, 98.83% conversion and 99.26% selectivity were achieved even at mild conditions of 60 °C and 0.1 MPa. After 10 cycles of reuse, the recycled MPNPs-[ImR2NH2][ZnBr3] demonstrated the same high-efficiency activity as the fresh catalyst, as well as excellent stability and magnetic separation. Based on the density functional theory (DFT) calculations, the intramolecular synergy of ternary active sites and the catalytic mechanism of bimolecular activation based on the multifunctional structure were proposed. This excellent catalyst was attributed to the intramolecular synergy of ternary active sites, large loading of active centers, lower internal diffusion resistance, the inert protective effect of polystyrene layer and the easily magnetic separation of CoFe2O4, highlighting a new direction for green catalytic chemistry.