Regulation of Novel Multi-Center Ionic Liquids for Synergetically Catalyzing CO2 Conversion into Cyclic Carbonates

A family of novel multi-center ionic liquids (ILs) were designed for the target of efficient transformation of CO2 into cyclic carbonates. The multi-center structures could expose more active sites than single-center ones in cycloaddition reaction. Among these ILs, with the chain-regulation strategy, the multi-center hexabutylimidazole bromobenzene (BIM-6) exhibited the performance with 95 % propylene epoxide (PO) conversion and 99 % selectivity (130 degrees C, 2.5 MPa, ILs amount 0.15 mol%, 1 h). Moreover, the multi-center ILs showed good reusability after 5 cycles and extensive suitability for different terminal epoxides. Density functional theory (DFT) and noncovalent interactions (NCI) illustrated that hydrogen-bond formed between the multi-center ILs and epoxides, together with hindrance of side chain lengths setting bromide free, synergistically activated reactants. Thus, the possible mechanism based on hydrogen-bond induction and hindrance regulation was proposed. This study provides a new approach for development of highly efficient ILs in the green chemical process