The heteronuclear cluster chemistry of the Group IB metals. Part 16. Metal exchange reactions in Group IB metal heteronuclear cluster compounds. Synthesis and structural characterization of the trimetallic hexanuclear cluster compounds [MM′Ru4(µ3-H)2{µ-Ph2P(CH2)nPPh2}(CO)12](M = Cu, M′= Ag or Au; M = Ag, M′= Au; n= 1 or 2) and X-ray crystal structure of [AuCuRu4(µ3-H)2{µ-Ph2P(CH2)2PPh2}(CO)12]

Abstract

Treatment of dichloromethane solutions of the heteronuclear cluster compounds [M₂Ru₄(µ₃-H)₂{µ-Ph₂P(CH₂)_nPPh₂}(CO)₁₂](M = Cu or Ag, n= 1 or 2) with dichloromethane solutions containing the appropriate quantities of the complex [Ag(NCMe)₄]PF₆ or [AuCl(SC₄H₈)] results in the replacement of either one or both of the Group IB metals M by silver or gold atoms. The products from these Group IB metal exchange reactions are obtained in ca. 65–75% yield. The synthetic approach is especially useful for the preparation of the novel trimetallic species [MM′Ru₄(µ₃-H)₂{µ-Ph₂P(CH₂)_nPPh₂}(CO)₁₂](M = Cu, M′= Ag or Au; M = Ag, M′= Au; n= 1 or 2). These clusters have all been characterized by IR and NMR spectroscopy and the structure of [AuCuRu₄(µ₃-H)₂{µ-Ph₂P(CH₂)₂PPh₂}(CO)₁₂] has been determined by a single-crystal X-ray diffraction study. The spectroscopic data show that all of the clusters in the series adopt similar structures. The metal framework consists of a tetrahedron of ruthenium atoms, with one face capped by a Group IB metal and one of the MRu₂ faces of the MRu₃ tetrahedron so formed further capped by the second Group IB metal, to give an overall capped trigonal-bipyramidal metal core geometry. The other two MRu₂ faces are both capped by a triply bridging hydrido ligand and the bidentate diphosphine ligand bridges the two coinage metals. Each ruthenium atom is ligated by three essentially linear CO groups. In each case, the lighter of the pair of Group IB metals occupies the site of higher co-ordination number and the heavier is in the position of lower co-ordination number. Interestingly, variable-temperature NMR spectroscopic studies show that the metal frameworks of [MM′Ru₄(µ₃-H)₂{µ-Ph₂P(CH₂)_nPPh₂}(CO)₁₂] are stereochemically rigid in solution at ambient temperature, in marked contrast to the dynamic behaviour involving intramolecular coinage-metal site-exchange, which has been previously reported for analogous bimetallic species.