Synthesis of Bifunctional Porphyrin Polymers for Catalytic Conversion of Dilute CO to Cyclic Carbonates.

Development of efficient solid catalysts for catalytic conversion of dilute CO is of extreme importance for carbon capture and utilization. We report the synthesis of bifunctional polymers co-incorporated with porphyrin-Zn as Lewis acid sites and Br as nucleophiles for the cycloaddition of dilute CO with epoxides in this work. It was found that the Br/Zn ratio has a volcano relation with the activity of bifunctional polymers in a cycloaddition reaction, indicating the synergy effect between Lewis acid sites and nucleophiles. The turnover frequency (TOF) of the bifunctional polymer is more than four-fold that of the physical mixture of tetrabutylammonium bromide and porphyrin-Zn-incorporated polymer, implying the enhanced cooperation between Br and porphyrin-Zn in the polymer network. The bifunctional polymer with optimized Br/Zn afforded 99% conversion, 99% selectivity, and a TOF as high as 12,000 h for the cycloaddition of CO and propylene oxide, which is among the most active solid catalysts ever reported. Furthermore, the bifunctional polymer could efficiently catalyze the cycloaddition of epichlorohydrin with dilute CO (7.5% CO balanced by N) even under ambient conditions, demonstrating its potential application in industrial-scale production.