Yldiide Ligands as Building Blocks for Polynuclear Coinage Metal Complexes: Metal Squares, Triangles and Chains

Yldiides have unique electronic properties and donor abilities, but as ligands in transition metal complexes they are scarcely represented in the literature. Here, the controlled synthesis of a series of polynuclear gold yldiide complexes derived from triphenyl(cyanomethyl)phosphonium bromide, [Ph3PCH2CN]Br, under mild conditions is described. Anionic dinuclear NBu4[(AuX)2{C(CN)PPh3}] (X=Cl, C6F5) or trinuclear derivatives NBu4[Au3X2{C(CN)PPh3}] bearing terminal chloride or pentafluorophenyl groups and bridging yldiide ligands have been prepared. These compounds evolve in solution giving rise to the formation of an unprecedented tetrameric gold cluster, [Au4{C(CN)PPh3}4], by the loss of the gold complex NBu4[AuX2]. This gold cluster can also be prepared in high yield by a transmetalation reaction from the analogous tetrameric silver cluster, and two geometric isomers have been characterised, their formation dependent on the synthetic route. The triphenylphosphonium cyanomethyldiide ligand has also been used to build different dinuclear and trinuclear cationic complexes bearing phosphine or diphosphine ancillary ligands and bridging yldiide moieties. Further coordination through the cyano group of the yldiide ligand gives heterometallic trinuclear or pentanuclear derivatives. Structural characterisation of many of these compounds reveals the presence of complex molecular systems stabilised by gold⋅⋅⋅gold interactions and bridging yldiide ligands.