Diferrate [Fe₂ (CO)₆ (μ-CO){μ-P(aryl)₂ }]^- as Self-Assembling Iron/Phosphor-Based Catalyst for the Hydrogen Evolution...

This work is focused on the identification and investigation of the catalytically relevant key iron species in a photocatalytic proton reduction system described by Beller and co-workers. The system is driven by visible light and consists of the low-cost [Fe₃ (CO)₁₂ ] as catalyst precursor, electron-poor phosphines P(R)₃ as co-catalysts, and a standard iridium-based photosensitizer dissolved in a mixture of THF, water, and the sacrificial reagent triethylamine. The catalytic reaction system was investigated by operando continuous-flow FTIR spectroscopy coupled with H₂ gas volumetry, as well as by X-ray absorption spectroscopy, NMR spectroscopy, DFT calculations, and cyclic voltammetry. Several iron carbonyl species were identified, all of which emerge throughout the catalytic process. Depending on the applied P(R)₃ , the iron carbonyl species were finally converted into [Fe₂ (CO)₆ (μ-CO){μ-P(R)₂ }]^- . This involves a P-C cleavage reaction. The requirements of P(R)₃ and the necessary reaction conditions are specified. [Fe₂ (CO)₆ (μ-CO){μ-P(R)₂ }]^- represents a self-assembling, sulfur-free [FeFe]-hydrogenase active-site mimic and shows good catalytic activity if the substituent R is electron poor. Deactivation mechanisms have also been investigated, for example, the decomposition of the photosensitizer or processes observed in the case of excessive amounts of P(R)₃ . [Fe₂ (CO)₆ (μ-CO){μ-P(R)₂ }]^- has potential for future applications.