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 one-step multicomponent strategy for constructing PSIL catalysts, which would be promising to find wide applications in catalysis and organic synthesis field.
The immobilization of homogeneous catalysts has always been a hot issue in the field of catalysis. In this paper, in an attempt to immobilize the homogeneous [Ni(Me6Tren)X]X (X = I, Br, Cl)-type catalyst with porous organic polymer (POP), the heterogeneous catalyst PBTP-Me6Tren(Ni) (POP-Ni) was designed and constructed by quaternization of the porous bromomethyl benzene polymer (PBTP) with tri[2-(dimethylamino)ethyl]amine (Me6Tren) followed by coordination of the Ni(II) Lewis acidic center. Evaluation of the performance of the POP-Ni catalyst found it was able to catalyze the CO2 cycloaddition with epichlorohydrin in N,N-dimethylformamide (DMF), affording 97.5% yield with 99% selectivity of chloropropylene carbonate under ambient conditions (80 °C, CO2 balloon). The excellent catalytic performance of POP-Ni could be attributed to its porous properties, the intramolecular synergy between Lewis acid Ni(II) and nucleophilic Br anion, and the efficient adsorption of CO2 by the multiamines Me6Tren. In addition, POP-Ni can be conveniently recovered through simple centrifugation, and up to 91.8% yield can be obtained on the sixth run. This research provided a facile approach to multifunctional POP-supported Ni(II) catalysts and may find promising application for sustainable and green synthesis of cyclic carbonates.
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