THE HETERONUCLEAR CLUSTER CHEMISTRY OF THE GROUP IB METALS .18. SYNTHESIS, STRUCTURAL CHARACTERIZATION AND DYNAMIC BEHAVIOR OF THE BIMETALLIC HEXANUCLEAR GROUP IB METAL CLUSTER COMPOUNDS [M(2)RU(4)H(2)(MU-DPPF)(CO)(12)] [M=CU, AG OR AU - DPPF=FE(ETA(5)-C(5)H(4)PPH(2))(2)] - X-RAY CRYSTAL-STRUCTURE OF [CU2RU4(MU(3)-H)(2)(MU-DPPF)(CO)(12)]

Treatment of a dichloromethane solution of the salt [N(PPh3)(2)](2)[RU (4)(mu-H)(2)(CO)(12)] with two equivalents of the complex [M(NCMe)(4)] PF6 (M = Cu or Ag) at -30 degrees C, followed by the addition of one e quivalent of 1,1'-bis(diphenylphosphino)ferrocene (dppf) affords the m ixed-metal clusters [M(2)RU(4)(mu(3)-H)(2)(mu-dppf) (CO)(12)] [M = CU (1) or Ag (2)] in ca 45-60% yield. The analogous gold-containing speci es [Au2Ru4H2(mu-dppf)(CO)(12)] (3) was obtained in ca 70% yield by tre ating an acetone solution of [N(PPh(3))(2)](2)RU(4)(mu-H)(2)(CO)(12)] with a dichloromethane solution of the complex [Au-2(mu-dppf)Cl-2], in the presence of TlPF6. The novel cluster compounds 1-3 have been char acterized by IR and NMR spectroscopy and the structure of 1 has been d etermined by a single-crystal X-ray diffraction study. The metal core structure of 1 consists of a tetrahedron of ruthenium atoms capped by a copper atom, with one of the CuRu2 faces of the CuRu3 tetrahedron so formed further capped by a second copper atom to give a Capped trigon al bipyramidal skeletal geometry. The other two CuRu2 faces of the CuR u3 tetrahedron are each capped by a triply bridging hydride ligand, th e bidentate diphosphine ligand bridges the two coinage metals and each ruthenium atom is bonded to three terminal CO groups. The spectroscop ic data of the silver- and gold-containing species 2 and 3 are closely similar to those of 1, which suggests that 2 and 3 adopt similar meta l core structures to that established for 1. However, the possibility that the capped trigonal bipyramidal metal framework of 3 is distorted by the dppf ligand towards a capped square-based pyramidal skeletal g eometry cannot be excluded with the evidence available. Variable-tempe rature H-1 and P-31{H-1} NMR studies show that, at ambient temperature s in solution, the metal frameworks of all of the clusters undergo dyn amic behaviour involving coinage metal site exchange, even though the two Group IB metals are linked together by the bidentate diphosphine l igand dppf. Free energies of activation (Delta G(double dagger)) at th e coalescence temperature of 47 +/- 1, 40 +/- 1 and ca 33 kJ mol(-1) h ave been calculated for the skeletal rearrangements from the coalescen ce temperatures observed in the variable-temperature P-31{H-1} NMR spe ctra of clusters 1, 2 and 3, respectively. These values of Delta G(dou ble dagger) are compared with those of structurally related analogous clusters. In addition, the dppf ligand attached to the coinage metals in each of 1-3 is also stereochemically non-rigid in solution at room temperature and it undergoes a process involving inversion of configur ation at the phosphorus atoms, together with twisting of the cyclopent adienyl rings. The skeletal rearrangement process and the fluxional be haviour of the dppf ligand are definitely independent for clusters 2 a nd 3.