Metalloporphyrin-based organic polymers for carbon dioxide fixation to cyclic carbonate

Abstract

A porphyrin-based organic polymer [(Por)OP] was prepared using a most convenient and simple method by condensation of pyrrole and terephthaldehyde in propanoic acid. A direct metallation of (Por)OP with metal acetate led to the formation of the corresponding metalloporphyrin-based organic polymer [M(Por)OP, (M = Zn, Co)]. The M(Por)OP bears dense catalytic sites of metalloporphyrin covalently linked in the skeleton and shows excellent catalytic performance toward cycloaddition of carbon dioxide (CO₂) to propylene oxide (PO) to give cyclic propylene carbonate (PC). All of the M(Por)OP-promoted cycloaddition reactions displayed remarkable selectivity to the cyclic carbonate without polycarbonate and other by-products. The effects of various reaction parameters on the catalytic performance of M(Por)OP were investigated systematically in terms of both the PC yield and turnover frequency. Moreover, owing to the covalent linkages between the catalytic sites of metalloporphyrin in the frameworks, the developed M(Por)OP is stable and insoluble in any commonly used organic solvents and behaves as a heterogeneous catalyst in CO₂ fixation. Also, the M(Por)OP can be readily separated from the product and reused.