The heteronuclear cluster chemistry of the Group 1B metals. Part 1. Structural similarities and differences among mixed-metal cluster compounds containing copper, silver, or gold atoms ligated by phosphines. X-Ray crystal structures of [CuRu4(µ3-H)3(CO)12(PMePh2)] and [CuRu3(CO)9(C2But)(PPh3)]

Abstract

Treatment of dichloromethane solutions of [N(PPh₃)₂][Ru₄(µ-H)₃(CO)₁₂] or [N(PPh₃)₂][Ru₃(CO)₉(C₂Bu^t)] with [M(NCMe)₄]PF₆(M = Cu or Ag) at –30 °C, followed by the addition of the desired phosphine ligand, affords the mixed-metal clusters [MRu₄(µ₃-H)₃(CO)₁₂L][M = Cu, L = PMePh₂(1) or PPh₃(2); M = Ag, L = PPh₃(3)], [{MRu₄(µ₃-H)₃(CO)₁₂}₂(µ-Ph₂PCH₂CH₂PPh₂)][M = Cu (6) or Ag (7)], and [MRu₃(CO)₉(C₂Bu^t)(PPh₃)][M = Cu (10) or Ag (11)] in ca. 70–80% yield. In dichloromethane solution, [N(PPh₃)₂][Ru₄(µ-H)₃(CO)₁₂], [N(PPh₃)₂][Ru₃(CO)₉(C₂Bu^t)], and [N(PPh₃)₂][Fe₃(µ-COMe)(CO)₁₀] also react directly with [MX(PPh₃)](M = Cu or Au, X = Cl; M = Ag, X = I) or [Au₂(µ-Ph₂PCH₂PPh₂)Cl₂], in the presence of TIPF₆, to give reduced yields of (2), (3), (10), and (11), two analogous gold–ruthenium clusters [AuRu₄(µ-H)₃(CO)₁₂(PPh₃)](8) and [{AuRu₄(µ-H)₃(CO)₁₂}₂(µ-Ph₂PCH₂PPh₂)](9), and the series of clusters [MFe₃(µ-COMe)(CO)₁₀(PPh₃)][M = Cu (15), Ag (16), or Au (17)], as appropriate. All of these clusters have been characterized by i.r. and n.m.r. spectroscopy and the structures of (1) and (10) have been established by single-crystal X-ray diffraction studies. Clusters (8) and (9) adopt different metal-core structures to those of (1)–(3), (6), and (7), with the Au(PR₃)(R = alkyl or aryl) fragment(s) in (8) and (9) bridging an edge of a ruthenium tetrahedron, whereas the M(PR₃)(M = Cu or Ag) unit(s) in (1)–(3), (6), and (7) cap a face of a similar basic Ru₄ tetrahedron. However, clusters (15), (16), and (17) all have the same skeletal geometry, with the M(PPh₃)(M = Cu, Ag, or Au) groups bridging an edge of an iron triangle, and species (10) and (11) show the same ‘butterfly’ metal-core arrangement as that previously established for the analogous gold species [AuRu₃(CO)₉(C₂Bu^t)(PPh₃)]. The pentanuclear cluster [CuRu₄(µ₃-H)₃(CO)₁₂(PMePh₂)](1) has a trigonal-bipyramidal metal-core geometry, with the copper atom occupying an apical site [Cu–Ru 2.717(1)–2.749(1), Ru–Ru 2.788(1)–2.970(1)Å]. Each ruthenium atom is ligated by three terminal CO groups and the copper atom by the PMePh₂ ligand. All three CuRu₂ faces of the metal skeleton are capped by triply-bridging hydrido ligands [mean Cu–H 1.93(6), mean Ru–H 1.81(6)Å]. The tetranuclear cluster [CuRu₃(CO)₉(C₂Bu^t)(PPh₃)](10) adopts a ‘butterfly’ metal-core structure (interplanar angle 115.7°), with the copper atom occupying a ‘wing-tip’ site. The two Cu–Ru bond lengths are equal [2.603(1)Å] and the side of the Ru₃ triangle which is bridged by the Cu(PPh₃) fragment [2.762(1)Å] is significantly shorter than the other two Ru–Ru distances [2.819(1) and 2.808(1)Å]. The t-butylacetylide ligand lies on the convex side of the ‘butterfly’ metal core, interacting with all three ruthenium atoms via one σ bond to the ‘wing-tip’ ruthenium site and two π bonds to the two ruthenium atoms which form the ‘body’ of the ‘butterfly’. Each ruthenium atom is ligated by three CO groups, two of which also exhibit short Cu–C contacts [2.496(7) and 2.552(7)Å].