Brønsted acid improved cycloaddition of carbon dioxide to propylene oxide

New and highly efficient catalyst systems of 5,10,15,20-tetra(4-carboxyphenyl)porphyrinato cobalt salt (TCPPCo(III)X/PTAT, X = CF3COO, OAc, Br, Cl) were developed to catalyze the coupling reaction of carbon dioxide and propylene oxide. It was discovered that the Brønsted acid can accelerate this reaction. A kinetic study demonstrated that the coupling reaction follows the rule of first order reaction and the reaction with addition of organic acid has lower activation energy than that without organic acid. This promotion can be attributed to the additional activation of epoxides by hydrogen bonding.

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► TCPPCo(III)CF3COO/PTAT was effective for the reaction of propylene oxide and CO2.
► Brønsted acids were found to have promotion on this coupling reaction.
► A kinetic study was carried out to further reveal this coupling reaction.
► A reasonable reaction mechanism was proposed.