The heteronuclear cluster chemistry of the Group 1B metals. Part 11. Effect of the nature of the bidentate diphosphine ligand on the metal framework structures of the gold heteronuclear cluster compounds [Au2Ru4(µ3-H)(µ-H){µ-Ph2P(CH2)nPPh2}(CO)12](n= 1–6). X-Ray crystal structures of [Au2Ru4(µ3-H)(µ-H){µ-Ph2P(CH2)nPPh2}(CO)12](n= 1 or 2)

Abstract

Treatment of acetone solutions of the salt [N(PPh₃)₂]₂[Ru₄(µ-H)₂(CO)₁₂] with a dichloromethane solution of the appropriate complex [Au₂{µ-Ph₂P(CH₂)_nPPh₂}Cl₂](n= 1–6), in the presence of TIPF₆, affords the mixed-metal cluster compounds [Au₂Ru₄(µ₃-H)(µ-H){µ-Ph₂P(CH₂)_nPPh₂}(CO)₁₂][n= 1, (2); 2, (3); 3, (4); 4, (5); 5, (6); or 6, (7)] in ca. 60–70% yield. X-Ray diffraction studies on (2) and (3) reveal that the formal replacement of the two PPh₃ ligands attached to the Au atoms in [Au₂Ru₄(µ₃-H)(µ-H)(CO)₁₂(PPh₃)₂](1) by Ph₂P(CH₂)_nPPh₂(n= 1 or 2) alters the capped trigonal-bipyramidal skeletal geometry adopted by (1). The cluster (2) crystallizes in two forms, monoclinic and orthorhombic, but X-ray diffraction studies on both forms show that the molecular structures adopted by (2) are closely similar in each case. The metal core of (2) consists of a square-based pyramid, defined by two Au atoms and two Ru atoms in the basal plane and a Ru atom at the apex, with the Ru₃ face of this Au₂Ru₃ unit capped by a Ru atom [Au–Au 2.823(1), Au–Ru 2.682(1)–2.947(2), Ru–Ru 2.791(2)–3.006(2)Å for the monoclinic form and Au–Au 2.833(2), Au–Ru 2.691(3)–2.862(3), Ru–Ru 2.805(4)–3.037(3)Å for the orthorhombic form]. The Ph₂PCH₂PPh₂ ligand bridges the two Au atoms, one hydrido ligand caps a Ru₃ face and one bridges a Ru–Ru edge of the metal framework, and each Ru atom is ligated by three terminal CO groups. The skeletal geometry of (3) is reasonably similar to that exhibited by (1), but one of the Au–Ru distances [3.446(4)Å] is too long for any significant bonding interaction between the two atoms. Thus, the metal framework of (3) is somewhat distorted towards a capped square-based pyramid [Au–Au 2.828(4), Au–Ru 2.777(4)–2.965(4), Ru–Ru 2.782(4)–3.008(4)Å]. Variable-temperature ¹H and ³¹P-{¹H} n.m.r. studies show that, at ambient temperature in solution, the metal cores of (3)–(7) all undergo dynamic behaviour involving gold atom site exchange.