SYNTHESIS, CRYSTAL-STRUCTURES AND DYNAMIC BEHAVIOR OF THE PENTANUCLEAR MIXED-METAL CLUSTER COMPOUNDS U3(MU-H)-(MU(3)-COME)(MU-PH2P(CH2)(N)PPH2)(CO)(9)] (N=1 OR 5)

The cluster compound [Ru-3(mu-H)(3)(mu(3)-COMe)(CO)(9)] reacted with t he complex [Au-2{mu-Ph2P(CH2)(n)PPh2}Me-2] (n = 1 or 5) in diethyl eth er solution to afford the new mixed-metal cluster compounds u3(mu-H)(m u(3)-COMe)-{mu-Ph2P(CH2)(n)PPh2}(CO)(9)] (n = 1 1 or 5 2) in ca. 30-40 % yield. Compounds 1 and 2 have been characterized by IR and NMR spect roscopy and by single-crystal X-ray diffraction. The X-ray diffraction studies show that the Au2Ru3 metal cores of 1 and 2 both adopt simila r distorted square-based pyramidal structures, with the basal plane de fined by the two Au atoms and two of the Ru atoms and the third Ru ato m forming the apex of the pyramid [Au-Au 2.878(1), Au-Ru 2.688(1)-2.86 3(1), Ru-Ru 2.887(1)-2.891(1) Angstrom for 1 and Au-Au 3.109(1), AuRu 2.716(3)-2.787(3), Ru-Ru 2.859(2)-2.895(3) Angstrom for 2]. The Ph2P(C H)(n)PPh2 (n = 1 or 5) ligand bridges the two Au atoms, the methoxycar byne caps the Ru-3 face and the hydride bridges the basal Ru-Ru edge o f the metal framework. Each ruthenium atom is bonded to three terminal carbonyl groups. Variable-temperature NMR spectroscopic studies sugge sted that the metal skeletons of 1 and 2 are stereochemically non-rigi d at high temperature in solution. The novel fluxional process is thou ght to involve a migration of the diphosphinedigold group around the t hree possible edge-bridging sites on the trigonal-planar triruthenium unit, together with a concomitant movement of the edge-bridging hydrid e ligand. Band-shape analysis of variable-temperature H-1 and C-13-{H- 1} NMR spectra afforded values of Delta G(double dagger) for these pro posed metal-core rearrangements of 67.1 +/- 0.2 (H-1) and 67.0 +/- 0.2 kJ mol(-1) (C-13-{H-1}) for 1 and 58.9 +/- 0.1 kJ mol(-1) (C-13-{H-1} ) for 2. These free energies of activation are surprisingly high compa red with those previously reported for skeletal rearrangements in gold -ruthenium heteronuclear cluster compounds.