Synthesis and electrochemistry of p-substituted phenyl diphenylphosphinite rhodium(I) complexes

Abstract

The electrochemical behaviour of a series of rhodium(I) complexes of the type [Rh(CH3COCHCOCH3)CO(Ph2POPh-p-R)], where R=H (1), CH3 (2), tBu(3) and Cl(4)] revealed an irreversible oxidation of Rh(I) to Rh(III), an irreversible oxidation of the phosphorus atom followed by the decomposition of the phosphinite ligand. An unexpected reaction occurred between the electrochemical internal standard, free ferrocene, in its ferricinium ion form and the radical cation of the oxidised diphenyl phosphinite, leading to uncharacteristic electrochemical behaviour. Electronic communication between different molecular fragment was confirmed by the linear relationships obtained between the Gordy group electronegativities of the R-groups on the phosphinites (χR) and the Epa of Rh and the phosphorus atoms as well as the binding energy (eV) (measured by XPS) of the Rh 3d and P 2p peak positions. V-shape correlations were found between the Hammett constants of the R-groups on the phosphinites (χR) and the oxidation potentials and binding energies. This shows the difference in stabilisation either resonance or inductive between the electrondonating and electronwithdrawing substituents.