Unlocking Metal-Ligand Cooperative Catalytic Photochemical Benzene Carbonylation: A Mechanistic Approach

A key challenge in green synthesis is the catalytic transformation of renewable substrates at high atom and energy efficiency, with minimal exergonicity (ΔG≈0). Non-thermal pathways, i.e., electrochemical and photochemical, can be used to leverage renewable energy resources to drive chemical processes at well-defined energy input and efficiency. Within this context, photochemical benzene carbonylation to produce benzaldehyde is a particularly interesting, albeit challenging, process that combines unfavorable thermodynamics (DG° = 1.7 kcal/mol) and the breaking of strong C-H bonds (113.5 kcal/mol) with full atom efficiency and renewable starting materials. Nevertheless, little progress has been made since this transformation was first reported, in 1980s and ’90s. By following a mechanistic approach, applying spectrophotochemical and computational tools, we sought to gain a detailed understanding of the non-thermal C-H activation of benzene using metal-ligand cooperative (MLC) PNP rhodium complexes. This allowed us to unlock catalytic MLC benzene carbonylation promoted by irradiation in the near-visible UV region (390 nm) for the first time.