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

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)Å) but which packs about a center of symmetry so that there are two close (3.141 (1)Å) 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 Me2AuCI produces Au3Cl3(μ-dpma) which has a bent Au3 chain (Au-Au distances 3.131 (1), 3.138 (1) Å; 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] [N03]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. © 1990, American Chemical Society. All rights reserved.