Rhodium-Catalyzed Formylation of Aryl Halides with CO2 and H2.

The reductive formylation of aryl iodides/bromides to aryl aldehydes using CO2/H2 is presented for the first time. It was realized over a catalytic system composed of RhI3 or RhI3/Pd(dppp)Cl2 (dppp = 1,3-bis(diphenyphosphino)propane) and PPh3 in the presence of Ac2O/Et3N at 100 °C, affording aromatic aldehydes in good to excellent yields, together with good functional-group tolerance and broad substrate scope. The reaction proceeds through three cascade steps, involving HCOOH formation, CO release, and formylation of aryl halides.