Mechanism of the Ir/Pd catalyzed photocarboxylation of aryl halides

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 Pd^II with the amine radical (generated by the reaction of cationic radical amine and Cs₂CO₃) and Ir^II 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.