Electrochemical studies of gold(I) and gold(III) complexes of bis(diphenylphosphines)

Abstract

Cyclic voltammograms of gold complexes of bis(diphenylphosphines) were recorded using a gold working electrode. The E_½ values vs. a saturated calomel electrode (s.c.e.)(and the peak-to-peak separations) for the PF₆ salts of the following complexes were obtained: bis[1,2-bis(diphenylphosphino)benzene]gold(I), 0.463 (37); bis[1,2-bis(diphenylphosphino)ethene]gold(I), 0.572 V (37); bis[1,2-bis(diphenylphosphino)ethane]gold(I), 0.458(30); bis[1,3-bisdiphenylphosphino)propane]gold(I), 0.752 V (35 Mv). The first couple is electrochemically reversible and the last three show quasi-reversibility for the two-electron redox process to form the corresponding gold(III) complex. Spectroelectrochemistry of bis[1,2-bis(diphenylphosphino)benzene]gold(I) revealed only two u.v.-absorbing species in solution, and the limiting spectra are those of the tetrahedral gold(I) complex and the square-planar gold(III) complex. A facile pseudo-rotation between the two geometries is proposed. Cyclic voltammetry of the chloride or bromide salt of bis[1,2-bis(diphenylphosphino)benzene]gold(I) demonstrated that halide ion adds to the gold (III) complex but dissociates from it upon reduction back to the starting gold(I) complex. Based on electrochemical behaviour, the order of increasing lability of the gold(III) complexes is as listed above.