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 degreesC) yields the trinuclear complex salts {[((Pr3P)-Pr-i)Au](3)[S2C6H4/3-(Me)]}BF4 (1, 3). From concentrated solutions warmed above 20 degreesC the neutral tetranuclear complexes {((Pr3P)-Pr-i)(2)Au-4[S2C6H4/3(Me)](2)} (2, 4) are crystallized in good yields. [((Pr3P)-Pr-i)(2)Au]BF4 (6) was identified as the byproduct of the ligand redistribution reaction which converts the tri- into the tetranuclear clusters. With {[(Ph3P)Au](3)O}BF4 no such ligand scrambling occurs and only the trinuclear complex salt {[(Ph3P)Au](3)(S2C6H4)}BF4 (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)(2)Au-4(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)(2)Au][Au(S2C6H4)(2)] is the main product of the reaction.