Sustainable synthesis of multifunctional porous metalloporphyrin polymers for efficient carbon dioxide transformation under mild conditions

Multifunctionalization of porous organic polymers (POPs) for working in concert on a substrate is now a research topic in CO2 catalysis, yet it remains challenging. This work describes a pre- and post-synthetic strategy to design metalloporphyrin-based azo-hierarchical porous ionic polymers (ZnTPP/QA-azo-PiPs), which were synthesized based on diazo-coupling reaction of tetra(4-aminophenyl) porphyrin zinc with tri/diphenols in aqueous solution under mild conditions, followed by etherification with quaternary ammonium bromide. This synthetic approach endows ZnTPP/QA-azo-PiP1 with features of an improved surface area (181 m2/g), hierarchical porosity, and high-density active sites. ZnTPP/QA-azo-PiP1 presented a noteworthy CO2 uptake of 1.77 mmol/g at 273 K and 1.0 bar and good CO2/N2 selectivity of 44.8. As expected, ZnTPP/QA-azo-PiP1 showed quantitative conversion and selectivity for a range of epoxides under mild conditions (1.0 MPa, 80 °C, 12 h) in the CO2 cycloaddition reaction. ZnTPP/QA-azo-PiP1 could been recycled easily and retained complete retention of activity and selectivity for over 7 cycles. Moreover, with efficacious activity in conversion of diluted CO2 (15% CO2 in 85% N2, v/v), ZnTPP/QA-azo-PiP1 could smoothly catalyze CO2-involved reaction to produce oxazolidinones and N-formylated amines under mild conditions. This work promotes sustainable synthesis of advanced multifunctional POPs and gives great promise for their application in synthetic transformations of CO2.