Polynuclear ((diphenylphosphino)methyl)phenylarsine bridged complexes of gold(I). Bent chains of gold(I) and a role for Au(I)-Au(I) interactions in guiding a reaction

Article abstract of DOI:10.1021/ja00169a028

The role of weak Au(I)-Au(I) interactions in determining the structure and reactivity of a set of new, ligand-bridged complexes is described. Addition of 2 equivs of Me₂SAuCl to dpma [dpma is bis((diphenylphosphino)methyl)phenylarsine] yields Au₂Cl₂(μ-dpma) which has its two gold ions widely separated (7.011 (1) A?) but which packs about a center of symmetry so that there are two close (3.141 (1) A?) Au-Au contacts between molecules. ³¹P NMR spectra indicate that this molecule self associates at low temperature in solution also. Treatment of Au₂Cl₂(μ-dpma) with further Me₂SAuCl produces Au₃Cl₃(μ-dpma) which has a bent Au₃ chain (Au-Au distances 3.131 (1), 3.138 (1) A?; Au-Au-Au angle, 110.9 (1)°). The reaction of Au₂Cl₂(μ-dpma) with ammonium hexafluorophosphate or thallium nitrate yields [Au₄Cl₂(μ-dpma)₂] [PF₆]₂ or [Au₄Cl₂(μ-dpma)₂] [NO₃]₂, respectively. These have bent Au₄ chains (Au-Au distances 2,965 (1), 3.096 (1); Au-Au-Au angle, 88.0 (1)° in the hexafluorophosphate salt) with terminal P-Au-Cl groups and the dpma ligands aligned so that phosphorus is trans to arsenic on the central two gold ions. Comparisons of the solid state, associated form of Au₂Cl₂(μ-dpma) and [Au₄Cl₂(μ-dpma)₂]²⁺ suggest that the initial stage of formation of the Au₄ chain involves association of the Au₂Cl₂(μ-dpma) units through Au-Au interactions, despite the presence of vacant coordination sites on the gold ions and lone pairs on the arsenic atoms. The role of empty p acceptor orbitals on gold favoring the bent chains is developed.