The heteronuclear cluster chemistry of the Group 1B metals. Part 13. Synthesis and structural characterization of the bimetallic hexanuclear Group 1B metal cluster compounds [M2Ru4(µ-CO)3(CO)10(PPh3)2](M = Cu, Ag, or Au). X-Ray structure analyses of [M2Ru4(µ-CO)3(CO)10(PPh3)2](M = Cu or Ag)

Abstract

Treatment of the salt [N(PPh₃)₂]₂[Ru₄(CO)₁₃]·thf (thf = tetrahydrofuran) with 2 equivalents of the complex [M(NCMe)₄]PF₆(M = Cu or Ag) at –30 °C, followed by the addition of 2 equivalents of PPh₃, affords the mixed-metal cluster compounds [M₂Ru₄(µ-CO)₃(CO)₁₀(PPh₃)₂][M = Cu (1) or Ag (2)] in ca. 35–40% yield. The analogous gold-containing species, [Au₂Ru₄(µ-CO)₃(CO)₁₀(PPh₃)₂](3), was obtained in ca. 65% yield by treating a dichloromethane solution of [N(PPh₃)₂]₂[Ru₄(CO)₁₃]·thf with a dichloromethane solution containing 2 equivalents of the complex [AuCl(PPh₃)] at –30 °C, in the presence of TIPF₆. Single-crystal X-ray diffraction studies on (1) and (2) show that both clusters exhibit similar capped trigonal-bipyramidal metal frameworks, consisting of a tetrahedron of ruthenium atoms with two Ru₃ faces capped by M(PPh₃)(M = Cu or Ag) units [Cu–Ru 2.608(2)–2.848(2), Ru–Ru 2.771(2)–2.981(2)Å for (1); Ag–Ru 2.806(1)–2.977(1), Ru–Ru 2.797(1)–3.074(1)Å for (2)]. Spectroscopic data suggest that the gold-containing cluster (3) also adopts a similar metal core structure. The skeletal geometries of clusters (1)–(3) are in marked contrast to the capped trigonal-bipyramidal skeletal geometries previously characterized in the solid state for the very closely related dihydrido clusters [M₂Ru₄H₂(CO)₁₂(PPh₃)₂](M = Cu, Ag, or Au), in which the Group 1B metals are in close contact. Thus, the formal replacement of two hydrido ligands in the latter clusters by the sterically more demanding CO group in (1)–(3) causes a fundamental change in the positions that the M(PPh₃)(M = Cu, Ag, or Au) units adopt on the ruthenium tetrahedra of these species.