Synthesis, X-ray structure and electrochemical oxidation of palladium(ii) complexes of ferrocenyldiphenylphosphine

Abstract

Four new complexes, [PdX(κ²-2-C₆R₄PPh₂)(PPh₂Fc)] [X = Br, R = H (1), R = F (2); X = I, R = H (3), R = F (4)], containing ferrocenyldiphenylphosphine (PPh₂Fc) have been prepared and fully characterised. The X-ray structures of complexes trans-1, cis-2 and cis-4, and that of a decomposition product of 4, [Pd(κ²-2-C₆F₄PPh₂)(μ-I)(μ-2-C₆F₄PPh₂)PdI(PPh₂Fc)] (5), have been determined. These complexes show a distorted square planar geometry about the metal atom, the bite angles of the chelate ligands being about 69°, as expected. The cis/trans ratio of 1–4 in solution is strongly dependent on solvent. The new complexes and the uncoordinated PPh₂Fc ligand were electrochemically characterised by cyclic and rotating disk voltammetry, UV-visible spectroelectrochemistry, and bulk electrolysis in dichloromethane and acetonitrile. In both cases, oxidation occurs at both the ferrocene and phosphine centres, but the complexes oxidise at more positive potentials than uncoordinated PPh₂Fc; subsequently, the metal–phosphorus bond is cleaved, leading to free PPh₂Fc⁺, which undergoes further chemical and electrochemical reactions.