Polymer grafted with asymmetrical dication ionic liquid as efficient and reusable catalysts for the synthesis of cyclic carbonates from CO₂ and expoxides

Polymer grafted with asymmetrical dication ionic liquid (IL) based on imidazolium and phosphonium ([P-Im-C₄H₈Ph ₃P]Br₂) was fabricated, and for the first time evaluated as catalyst for the synthesis of cyclic carbonates from epoxides and CO ₂ without using any co-catalyst and solvent. The catalyst showed much superior activity than monocation imidazolium and phosphonium ILs. At a low catalyst loading (0.38 mol%), high yield (96.8%) and selectivity (99.5%) of propylene carbonate can be obtained over [P-Im-C₄H₈Ph ₃P]Br₂ at 130 °C and 2.5 MPa in 4 h. The cooperation of nucleophilic attack of bromine anions as well as the activation of the two cations may contribute to the good activity of the catalyst. Furthermore, the catalyst shows excellent stability and reusability. It can be reused for up to five runs without any significant loss of catalytic activity after simple filtration.