VARIABLE-TEMPERATURE NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPIC STUDIESOF THE DYNAMIC BEHAVIOR OF THE MIXED-METAL CLUSTER COMPOUNDS [MM'RU4H2(MU-DPPF)(CO)(12)] [M=M'=CU, AG OR AU, M=CU, M'=AU, DPPF=FE(ETA(5)-C(5)H(4)PPH(2))(2)] AND THE CRYSTAL-STRUCTURES OF [MM'RU4H2(MU-DPPF)(CO)(12)] (M=CU OR AU, M'=AU)

The free energies of activation (delta G(++)) for the fluxional proces ses in the clusters [M(2)Ru(4)H(2)(mu-dppf)(CO)(12)] [M=Cu 1, AG 2 or Au 3; dppf=1.1'-bis(diphenylphosphino)ferrocene] have been determined by band-shape analysis of variable-temperature H-1 or P-31-{H-1} NMR s pectra. In solution, the dppf ligand attached to the coinage metals in each of 1-3 undergoes dynamic behaviour involving inversion at the ph osphorus atoms, together with twisting of the cyclopentadienyl rings, and values of 47.0 plus or minus 0.2, 51.5 plus or minus 0.1 and 48.8 plus or minus 0.2kJmol(-1) were obtained for delta G(++) of this fluxi onal process in 1-3, respectively. The metal cores of these three clus ters are also stereochemically non-rigid in solution and values of del ta G(++) of 47.7 plus or minus 0.2 and 39.9 plus or minus 0.4kJmol(-1) have been calculated for a coinage-metal site-exchange process in 1 a nd 2, respectively. The new trimetallic cluster [AuCuRu4(mu(3)-H)(2)(m u-dppf)(CO)(12)]4, which is closely related to the bimetallic clusters 1-3, has been synthesized in ca. 40% yield by treating [Cu2Ru4(mu(3)- H)(2)(mu-dppf)(CO)(12)] with the complex [AuCl(SC4H8)]. Variable-tempe rature H-1 NMR studies on 4 demonstrate that the dppf fluxion still oc curs in solution (delta G(++) 49.2 plus or minus 0.2kJmol(-1)), but th e metal skeleton of the cluster is stereochemically rigid, which is in marked contrast to those of the bimetallic analogues 1-3. The structu res of [MM'Ru4H2(mu-dppf)(CO)(12)] (M=Cu or Au, M'=Au) have been estab lished by single-crystal X-ray diffraction studies. The metal framewor k of 4 consists of a tetrahedron of ruthenium atoms with one face capp ed by the copper atom and one CuRu2 face of the CuRu3 tetrahedron so f ormed is capped by the gold atom to give an overall capped trigonal-bi pyramidal metal-core geometry [Cu-Au 2.641(1), Cu-Ru 2.755(1)-2.909(2) , Au-Ru 2.780(1) and 2.815(1), Ru-Ru 2.783(1)-2.998(1) angstroms]. The other two CuRu2 faces are capped by triply bridging hydrido ligands, the dppf ligand bridges the two coinage metals and each ruthenium atom is bonded to three terminal CO groups. The skeletal geometry of 3 is reasonably similar to that of 4, with a second gold atom replacing the copper atom. However, one of the Au-Ru distances [3.558(2)angstroms] is too long for any significant bonding interaction between the two me tal atoms, so the metal framework of 3 is somewhat distorted towards a capped square-pyramid [Au-Au 2.901(1), Au-Ru 2.771(1)-2.846(1), Ru-Ru 2.775(2)-3.016(1)angstroms]. As observed for 4, the bidentate diphosp hine ligand bridges the two group 11 metals in 3 and each ruthenium at om is bonded to three terminal CO groups, but one of the hydrido ligan ds bridges a Ru-Ru vector rather than capping an AuRu2 face.