Mechanism of the Ir/Pd catalyzed photocarboxylation of aryl halides

Abstract

The recent Ir/Pd co-catalyzed photo carboxylation of aromatic halides with CO2 has shown high efficiency and excellent functional group tolerance for preparing aromatic carboxylic acids and esters. With the aid of density functional theory (DFT) calculations, the carboxylation starts with two parallel steps, i.e., oxidative addition of aromatic halides on Pd0 and reductive quenching of the photocatalyst Ir(ppy)2(dtbpy)+ with amine. Thereafter, a successive oxidation of PdII with the amine radical (generated by the reaction of cationic radical amine and Cs2CO3) and IrII species occurs to generate Pd0, from which the carboxylation occurs easily via a coordination, Pd-C insertion step. The release of the carboxylate product then regenerates the catalyst.