Bottom-Up Construction of a CO2-Based Cycle for the Photocarbonylation of Benzene, Promoted by a Rhodium(I) Pincer Complex.

The use of carbon dioxide for synthetic applications presents a major goal in modern homogeneous catalysis. Rhodium-hydride PNP pincer complex 1 is shown to add CO2 in two disparate pathways: one is the expected insertion of CO2 into the metal-hydride bond, and the other leads to reductive cleavage of CO2, involving metal-ligand cooperation. The resultant rhodium-carbonyl complex was found to be photoactive, enabling the activation of benzene and formation of a new benzoyl complex. Organometallic intermediate species were observed and characterized by NMR spectroscopy and X-ray crystallography. Based on the series of individual transformations, a sequence for the photocarbonylation of benzene using CO2 as the feedstock was constructed and demonstrated for the production of benzaldehyde from benzene.