Variations in the chain structure of cationic (phosphine)gold(I) dialkyldithiophosphate complexes

Treatment of dithiophosphoric acid diesters (RO)₂P(S)SH with appropriate quantities of tris[(phosphine)gold(I)]oxonium tetrafluoroborates {[(R′₃P)Au]₃O}⁺ BF₄^- in dichloromethane gives di-or trinuclear complexes of the types {(RO)₂P[SAu(PR′₃)]_2/3}^+/2+ (2) BF₄^- as colourless, crystalline salts. As determined by single crystal X-ray diffraction studies, in the 1:2 complexes (with R = R′ = Me and R′ = Et, R = Ph and o-Tol), each gold atom is attached to a different sulfur atom, but with short intracationic Au-Au contacts. These cations are associated to form strings through intermolecular Au-Au contacts in the first case (R = Et), but through additional Au-S contacts in the second (R = Ph). For R = o-Tol, the cations are not associated at all owing to steric hindrance. This result is indicative of very small energy differences between the two modes of association. The 1:3 complexes are fluxional in solution and show virtually equivalent R₃PAu groups in the NMR spectra at 20°C, but at low temperature non-equivalent ligands can be distinguished as shown previously for analogous dithiophosphinate derivatives.