[HDBU]Br@P-DD as Porous Organic Polymer-Supported Ionic Liquid Catalysts for Chemical Fixation of CO2 into Cyclic Carbonates

The chemical fixation of CO2 into high value-added cyclic carbonates is of significant potential and sustainability to address the energy and ecological issues. [HDBU]Br@P-DD-m/n, a series of porous organic polymer-supported ionic liquids (PSILs), were fabricated in this work through a one-pot four-component reaction of DMAEMA, DVB, 4-bromobutyric acid, and DBU. The formation of [HDBU]Br and construction of the P-DD polymer network proceeded concurrently with the support of the in situ-formed IL being achieved simultaneously. Characterization of the PSILs by IR, ICP, BET, SEM, and TGA etc. showed that the as-prepared catalysts possessed versatile hierarchical porosity with varying ionic densities and excellent thermostability. The porosity of the copolymer skeleton was found to be affected by the accompanying formation of [HDBU]Br. The PSILs were then evaluated as catalysts for the cycloaddition reaction of CO2 with epoxides, among which [HDBU]Br@P-DD-4/1 showed the optimal performance under atmospheric pressure and solvent-/cocatalyst-free conditions (95% yield and 99% selectivity for CO2 cycloaddition with epichlorohydrin). By correlating the performance and structures of the catalysts, the synergistic effect of the tertiary amine, [HDBU]Br, and pore distribution was demonstrated. In addition, the catalyst was found to be applicable in synthesizing a range of differently substituted carbonates in good to excellent yields. Finally, the catalyst could be recovered readily and good catalytic activity was still observed after use for 6 runs. The work not only provided an active, reusable, and metal-free heterogeneous catalyst for the fixation of CO2 into cyclic carbonates but also developed a facile onestep multicomponent strategy for constructing PSIL catalysts, which would be promising to find wide applications in catalysis and organic synthesis field.