Novel porous organic polymers functionalized by metalloporphyrin and phosphonium salts for the efficient synergistic catalysis of CO2 conversion under mild conditions

Abstract

Functional porous organic polymers (POPs) have been extensively developed as heterogeneous catalysts for carbon dioxide conversion. However, exploring a general strategy to incorporate versatile active moieties into POPs is still a big challenge. In this study, a post-synthesis modification strategy was suggested for the fabrication of metalloporphyrin- and phosphonium-functionalized POPs. The as-prepared POP catalysts PPh₂PStR-PMtVPP (R = C2–C12) were characterized by FT-IR, SEM, TEM, XPS, TGA, ICP, and TPD measurements. The results demonstrated that the PPh₂PStR-PMtVPP catalysts were mesoporous and possessed a high adsorption capacity for CO₂, which was advantageous for the cycloaddition reaction of CO₂ and epoxides. Thanks to their rich Lewis acid sites and nucleophilic groups, PPh₂PStR-PMtVPP could cooperatively activate substrates and achieve efficient synergistic catalysis for CO₂ cycloaddition with epoxides. The effects of the phosphonium structure and different metal centers, as well as reaction conditions, on the catalytic performances of the functional POPs are discussed in detail. Under the optimized conditions, PPh₂PStD-PCoVPP-1 could efficiently and selectively catalyze the coupling of CO₂ and epoxides at 80 °C and 0.1 MPa CO₂. Moreover, PPh₂PStD-PCoVPP-1 could be easily separated and recycled five times without any obvious loss of catalytic activity. This study thus offers a powerful strategy for the fabrication of efficient bifunctional catalysts for CO₂ conversion.