Bridge-Mediated Regulation of Dicationic Ionic Liquids: Boosting Catalytic Conversion of CO2 Into Cyclic Carbonate Under Mild Conditions

The efficient catalytic conversion of CO 2 into valuable cyclic carbonates represents a promising green route utilizing CO 2 as a C1 resource. In this study, a series of dicationic imidazolium ionic liquids (DPImBr) were designed, and their microstructural properties were precisely modulated by strategically varying the bridge group structure. It was found that DPImBr with shorter bridge chains exhibited enhanced solubility and formed smaller clusters within the reaction system. This resulted in greater exposure of the catalytic active sites, which contributed to superior catalytic activity. Furthermore, functionalization of the bridge group proved effective in regulating the binding energy between cations and anions as well as the chemical hardness of the DPImBr. Among the synthesized catalysts, PRO-DPImBr, which possessed the highest chemical hardness, demonstrated the optimal catalytic performance. Under mild conditions (80°C, 1 MPa), PRO-DPImBr exhibited a propylene oxide (PO) conversion of 95% with 99% selectivity. This high performance was attributed to the presence of a hydrogen bond donor in PRO-DPImBr facilitating ring-opening of propylene oxide (PO) while stabilizing the alkoxide intermediate, thereby enhancing the reaction activity. By combining 1 H NMR spectroscopy and density functional theory (DFT) calculations, a synergistic catalytic mechanism was revealed in which both imidazolium C2-H and the bridged hydroxyl group could act as hydrogen donors to assist PO ring-opening with Br − , thereby promoting the overall reaction. The bridge-mediated strategy proposed in this work provides a novel design approach for developing efficient ionic liquid catalysts under mild reaction conditions. Graphical A series of dicationic imidazolium ionic liquids with varying bridge groups (x-DPImBr) were designed and synthesized, which demonstrated high efficiency in catalyzing conversion of CO 2 into cyclic carbonates under mild conditions (80°C, 1 MPa). The formation of ionic liquid clusters and their influence on catalytic activity were systematically investigated.