Phosphinofulvene Enolate Ligands in Ruthenium Complexes by Ferrocene Photolysis under Solar Radiation

Abstract

Ruthenium complexes containing a new type of phosphine ligand were obtained through photochemical transformations. The process involves the irradiation of (phosphinoferrocenylcarbonyl)ruthenium derivatives with visible light (tungsten halogen lamp) to yield complexes with κ2‐P,O phosphinofulvene enolate ligands after the formal loss of the “CpFe+” (Cp = cyclopentadienyl) entity. A tandem reaction that involves the irradiation of a mixture of a (hydroxymethyl)ferrocenylphosphine ligand and (arene)ruthenium precursors is also possible. The reaction proceeds through the coordination of the hydroxy phosphine ligands, evolution to hydrido ketone (or hydrido aldehyde) complexes and subsequent evolution to the fulvene derivatives. The process also occurs under solar radiation. The photolysis reaction was studied at different wavelengths of the visible spectrum by irradiation with light‐emitting diodes (LEDs). Positive results were obtained when irradiation was performed in the wavelength region corresponding to the metal‐to‐ligand charge‐transfer (MLCT) band that is characteristic of the acylferrocenyl moiety. The use of green light (λ = 530 nm) gave the best results, and the reaction did not proceed under higher‐wavelength light or in the dark. A non‐coordinated phosphinoferrocenylcarbaldehyde ligand also evolved under solar radiation, but a complex mixture was obtained; thus, the selectivity increases significantly if the ruthenium centre is present.