Photoreactivity of tricarbonyl(cyclohexadienyl)iron cation in aqueous solution. Protonation induced by metal-to-ligand charge transfer excitation

The complex [(C6H7)Fe(CO)3]+ in aqueous solution undergoes a photodecomposition which leads to the formation of cyclohexadiene and Fe2+ with a quantum yield of φ=0.32 at λirr=280 nm. It is suggested that the reactive excited state is of the (Fe→C6H7) metal-to-ligand charge transfer (MLCT) type. MLCT excitation facilitates an electrophilic addition of a proton at the C6H7 ligand while in the ground state a nucleophilic attack is favoured.