Synergistic Bifunctionality in Zn (II)-Porphyrin-Based Imidazolium Functionalized Porous Organic Polymers for Efficient Catalysis of CO2-Epoxide Cycloaddition

Abstract

The development of bifunctional catalytic materials bearing Lewis acid and base activity sites toward the cycloaddition of CO₂ and epoxides to value-added cyclic carbonate under cocatalyst-free conditions is needed in particular. In this work, an imidazolium functionalized Zn (II)-porphyrin ZnTAEImP was first designed and synthesized. Subsequently, a series of porous organic polymers, named POP-ZnTAEImP/DVB(1:m) (m = 30, 50, 70), were prepared through the free-radical copolymerization of ZnTAEImP with divinylbenzene (DVB). The obtained POP-ZnTAEImP/DVB(1:m) exhibited a high specific surface area and good thermal stability. As bifunctional heterogeneous catalysts, POP-ZnTAEImP/DVB(1:m) showed excellent catalytic activities in CO₂ cycloaddition with epichlorohydrin under the condition of solvent-free. In particular, the POP-ZnTAEImP/DVB(1:50) demonstrated the highest catalytic activity (TON = 2880) and was applicable to a variety of epoxides. Furthermore, only a slight decrease in catalytic activity was observed after five cycles. Activation energy (E_a) for this reaction was determined to be 52.4 kJ/mol. This work provides a valuable strategy for designing efficient binary heterogeneous catalysts for the high-efficiency fixation of CO₂.