Urea-Functionalized Imidazolium-Based Ionic Polymer for Chemical Conversion of CO2 into Organic Carbonates

Conversion of carbon dioxide (CO2) into useful chemicals is one of promising approaches to reduce global warming and the energy crisis. It is pivotal to develop heterogeneous catalytic systems containing task-specific active sites for chemical transformation of CO2. Herein, we report a urea-functionalized imidazolium-based ionic polymer (UIIP) for metal-, solvent- and additive-free conversion of CO2 into cyclic carbonates. UIIP was readily obtained through simple urea-forming condensation reaction. The high density of urea groups in the host backbone function as hydrogen bond donors to activate epoxides and CO2, while charge-balanced bromide anions serve as nucleophiles to encounter the epoxides from less sterically hindered carbon atom: they cooperatively facilitate ring opening of the epoxides. UIIP exhibits outstanding catalytic activity, superior recyclability and high stability in the cycloaddition reaction of CO2 under mild conditions. A detailed mechanistic insight into the effects of urea groups on the activation of both CO2 and epoxide has been elucidated by DFT calculations.