New Phosphino Fulvene-enolate Ligands in Ruthenium Complexes by Ferrocene Photolysis under Solar Radiation

Ruthenium complexes that contain a new type of phosphine ligand have been obtained by means of a photochemical transformation. The process involves the irradiation with visible light (tungsten halogen lamp) of ferrocenyl phosphino-carbonyl ruthenium derivatives to yield complexes with kappa2-P,O phosphino fulvene-enolate ligands after the formal loss of the 'CpFe+' entity. A tandem reaction is also possible that involves irradiation of a mixture of ferrocenyl hydroxyphosphine ligands and ruthenium arene precursors. The reaction takes place by coordination of the hydroxyphosphine ligands, evolution to hydrido-ketone (or hydrido-aldehyde) complexes and subsequent evolution to the fulvene derivatives. The process also takes place on using solar radiation. The photolysis reaction has been studied at different wavelengths of the visible spectrum by irradiation with LEDs. Positive results were obtained when irradiation was carried out in the region of wavelengths corresponding to the MLCT band that is characteristic of the acyl-ferrocenyl moiety. The use of green light (530 nm) gave the best results and the reaction did not take place on using higher wavelengths or in the dark. A non-coordinated ferrocenyl phosphino-aldehyde ligand also evolved under solar radiation but a complex mixture was obtained, thus demonstrating a significant increase in the selectivity when the ruthenium centre is present.