New pathways to compact tetragold(I) bis(phenylene-1,2-dithiolate) complexes with tertiary phosphine and isonitrile ligands

Treatment of phenylene-1,2-dithiol (or its 4-methyl derivative) with equimolar quantities of tris[(triisopropylphosphine)gold]oxonium tetrafluoroborate under mild conditions (in dichloromethane, -20 to +20 °C) yields the trinuclear complex salts {[(ⁱPr₃P)Au]₃[S₂C₆H_{4 /3}-(Me)]}BF₄ (1, 3). From concentrated solutions warmed above 20 °C the neutral tetranuclear complexes {(_iPr₃P)₂Au₄S₂C₆ H_4/3(Me)]₂} (2, 4) are crystallized in good yields. [(ⁱPr₃P)₂Au]BF₄ (6) was identified as the byproduct of the ligand redistribution reaction which converts the tri- into the tetranuclear clusters. With {[(Ph₃P)Au]₃O}BF₄ no such ligand scrambling occurs and only the trinuclear complex salt {[(Ph₃P)Au]₃(S₂C₆H₄)}BF ₄ (5) is formed. The structures of 2 and 4 have been determined by single-crystal X-ray diffraction studies. Although the crystals are not isomorphous, the molecules are almost superimposable. In the ligand framework, the four gold atoms form two edge-sharing, almost equilateral triangles which allow for tight aurophilic bonding. A similar tetranuclear cluster, [(RNC)₂Au₄(S₂C₆H₄)₂ ] (7; R = cyclohexyl), is generated in low yield in the reaction of (RNC)AuCl with C₆H₄(SNa)₂. It has been isolated as a cocrystallizate with the (isocyanide)(carbene)gold(I) complex salt {(RNC)Au[C(NHR)₂]}Cl (8) present in the reaction mixture, and the structure of the dichloromethane solvate has been determined. The components are aggregated in strings via aurophilic contacts following the sequence ...(7)(8)(8)(7)(8)(8)... The deep green gold(I)/ gold(III) salt [(RNC)₂Au] [AuS₂C₆H₄)₂] is the main product of the reaction.