Neutral gold(I) complexes with mixed phosphorus ligands

The reaction of compounds (R₃P)AuMe with diphenylphosphinous acid Ph₂P(O)H affords methane and neutral complexes of the type (R₃P)AuP(O)Ph₂ (1a: R = Me; Ib: R = Ph; le: R = o-Tol). la, b are obtained in high yield, but the yield of le is lower owing to a side-reaction which leads to a different product: Ph₂P(OH)-Au-P(O)Ph₂ (2). The crystal structure of la was determined by a single-crystal X-ray diffraction study. The compound is a monomer with a linear P-Au-P' axis and the phosphane and phosphinite ligands in a staggered conformation. In solution (CHCl₃, CH₂Cl₂) compounds la-c undergo a ligand redistribution, establishing equilibria that involve ionic isomers of the type [(R₃P]2Au]⁺⁺ [Au-(P(O)Ph₂)₂]-, which are readily identified through their NMR data. The analogous reaction of (R₃P)AuMe with dimethylphosphite (MeO)₂P(O)H gives methane and the corresponding dimethylphosphites of the type (R₃P)AuP(O}(OMe)₂ (₃a: R = Me; 3b: R = Ph; 3c: R = o-Tol). The crystal structure of 3b has also been determined. It features a linear structure with an eclipsed conformation of the ligands. In polar solvents (CHCL₃, methanol) there is again an equilibrium between neutral and ionic isomers, the latter comprising bis(phosphane)gold cations [(R₃P)₂Au]⁺ and (Au[P(O)-(OMe)₂]₂)^- anions, as confirmed by NMR spectroscopy and mass spectrometry.