Heteropolymetallic complexes of 1,1′-bis(diphenylphosphino)ferrocene (dppf): VII. Redox behaviour of dppf

Abstract

The electrochemical oxidation of 1,1′-bis(diphenylphosphino)ferrocene (dppf) at a platinum electrode in 1,2-dichloroethane has been studied by cyclic voltammetry, controlled potential electrolysis, and 31P NMR spectroscopy. The compound undergoes a ferrocene-based reversible oxidation, which is followed by a fast chemical reaction, involving the phosphorus substituent on the cyclopentadienyl rings, to give dppfO, dppfO 2, dppfH + and dppfH 2 2+. Kinetic data suggest that the reaction involes a reversible intramolecular electron transfer between the ferrocene core and the electron-rich substituents to give a phosphinium radical ion, which undergoes a second order rate-determining dimerization or a reaction with the parent compound to give a ferrocenylphosphine dimer cation radical, the ultimate fate of which is the formation of protonated and oxygenated dppf derivatives by nucleophilic attack by water present in the reaction medium. Evidence for the formation of the transient monomeric phosphinium radical was obtained by trapping it with 1,1′-diphenylethylene to give phosphorus-bonded monoalkene adducts of dppf.