The heteronuclear cluster chemistry of the group 1B metals. Part 10. Synthesis, structures, and dynamic behaviour of the bimetallic hexanuclear group 1B metal cluster compounds [M2Ru4(µ3-H)2{µ-Ph2As(CH2)nEPh2}(CO)12](M = Cu or Ag; E = As or P; n= 1 or 2). X-Ray crystal structure of [Cu2Ru4(µ3-H)2{µ-Ph2As(CH2)2PPh2}(CO)12]

Abstract

Treatment of a dichloromethane solution of the salt [N(PPh₃)₂]₂[Ru₄(µ-H)₂(CO)₁₂] with two equivalents of the complex [M(NCMe)₄]PF₆(M = Cu or Ag) at –30 °C, followed by the addition of one equivalent of the appropriate bidentate ligand Ph₂As(CH₂)_nEPh₂(E = As or P; n= 1 or 2) affords the mixed-metal cluster compounds [M₂Ru₄(µ₃-H)₂{µ-Ph₂As(CH₂)_nEPh₂}(CO)₁₂][M = Cu, E = P, n= 1 (1) or 2 (2); M = Ag, E = P, n= 1 (3) or 2 (4); M = Cu, E = As, n= 1 (5) or 2 (6); M = Ag, E = As, n= 1 (7) or 2 (8)] in ca. 60–75% yield. A single-crystal X-ray diffraction study on (2) reveals that the metal skeleton consists of a tetrahedron of ruthenium atoms capped by a Cu atom [Group 1B metal site M(2)], with one of the CuRu₂ faces of the CuRu₃ tetrahedron so formed further capped by the second Cu atom [Group 1B metal site M(1)] to give a capped trigonal-bipyramidal metal core geometry. The other two CuRu₂ faces of the cluster are both capped by triply bridging hydrido ligands, each ruthenium atom carries three terminal CO groups, and the Ph₂As(CH₂)₂PPh₂ ligand bridges the Cu–Cu vector. Disorder between As and P atoms suggests that two distinct structural isomers, the major one with the As atom attached to Cu(2) and the minor one with the As atom bonded to Cu(1), exist in the solid state. Spectroscopic data imply that (1) and (3)–(8) all adopt similar metal framework structures to (2). Variable-temperature ¹H and ³¹P-{¹H} n.m.r. studies demonstrate that two structural isomers exist in solution at low temperatures for both copper–ruthenium clusters (1) and (2) and that each of these pairs of isomers undergoes interconversion at ambient temperature by a dynamic process involving an intramolecular metal core rearrangement. The silver–ruthenium clusters (3) and (4) undergo similar dynamic behaviour at –30°C, but no spectra consistent with the ground-state structures could be obtained at lower temperatures. At higher temperatures, (3) and (4) both undergo two additional dynamic processes. The first involves a novel intramolecular exchange of the arsenic and phosphorus atoms in the Ph₂As(CH₂)_nPPh₂ ligands between the two silver atoms in each cluster and, as the temperature is raised further, the bidentate ligands undergo intermolecular exchange between clusters. N.m.r. spectroscopic data suggest that (6)–(8), which contain Ph₂As(CH₂)_nAsPh₂ ligands, also undergo fluxional processes involving Group 1B metal site-exchange at ambient temperature in solution and this behaviour has been directly observed for (7) by ¹⁰⁹Ag-{¹H} INEPT n.m.r. spectroscopy.