Co(Salen)-Based Hyper-Crosslinked Porous Ionic Polymer as Heterogeneous Synergistic Catalyst for the Cycloaddition of Co2 with Epoxides

Abstract

Integration of multiple active sites with task-specific functions in porous organic polymer is of significance in carbon dioxide (CO2) capture and catalysis. A bifunctional hyper-crosslinked porous ionic polymer [Co(salen)-HPiP)] bearing Co(salen) complexes and imidazolium ionic liquids was synthesized via a simple and low-cost synthetic method. Various techniques were used to characterize the as-prepared polymeric catalysts. Co(salen)-HPiP had an improved specific surface area, good CO2 adsorption capacity, high CO2/N2 adsorption selectivity, high density of nucleophilic/electrophilic sites (bromide /cobalt ions), as well as highly physiochemically stable structures. Co(salen)-HPiP was then employed as a synergistic heterogeneous catalyst for the solvent-additive-free synthesis of cyclic carbonates from CO2 and epoxides. Owing to the synergistic effects of its unique porous structure, high CO2 affinity and high-accessibility cobalt/bromide sites, Co(salen)-HPiP demonstrated outstanding catalytic performance in this transformation under mild conditions. To our delight, Co(salen)-HPiP also exhibited good substrate expansibility and robust reusability with retention of catalytic performance. Exhilaratingly, the intrinsic CO2/N2 selective adsorption rendered this catalytic protocol still highly effective for the cycloaddition of the simulated flue gas (15% CO2 in 85% N2, v/v). This work presented a sustainable strategy for the construction of multifunctional heterogeneous PiP-based catalysts and provided a promising platform for chemical fixation of real-world CO2.

Keywords: Salen complex, porous ionic polymers, Carbon dioxide, cycloaddition, Cyclic carbonates, synergistic catalysis