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.