Synthesis, crystal structures and dynamic behaviour of the pentanuclear mixed-metal cluster compounds [Au2Ru3(μ-H)(μ3-COMe){μ-Ph2P(CH2)nPPh2}(CO)9] (n =1 or 5) ‡

Abstract

The cluster compound [Ru3(µ-H)3(µ3-COMe)(CO)9] reacted with the complex [Au2{µ-Ph2P(CH2)nPPh2}Me2] (n = 1 or 5) in diethyl ether solution to afford the new mixed-metal cluster compounds [Au2Ru3(µ-H)(µ3-COMe){µ-Ph2P(CH2)nPPh2}(CO)9] (n = 1 1 or 5 2) in ca. 30–40% yield. Compounds 1 and 2 have been characterized by IR and NMR spectroscopy and by single-crystal X-ray diffraction. The X-ray diffraction studies show that the Au2Ru3 metal cores of 1 and 2 both adopt similar distorted square-based pyramidal structures, with the basal plane defined by the two Au atoms and two of the Ru atoms and the third Ru atom forming the apex of the pyramid [Au–Au 2.878(1), Au–Ru 2.688(1)–2.863(1), Ru–Ru 2.887(1)–2.891(1) A for 1 and Au–Au 3.109(1), Au–Ru 2.716(3)–2.787(3), Ru–Ru 2.859(2)–2.895(3) A for 2]. The Ph2P(CH)nPPh2 (n = 1 or 5) ligand bridges the two Au atoms, the methoxycarbyne caps the Ru3 face and the hydride bridges the basal Ru–Ru edge of the metal framework. Each ruthenium atom is bonded to three terminal carbonyl groups. Variable-temperature NMR spectroscopic studies suggested that the metal skeletons of 1 and 2 are stereochemically non-rigid at high temperature in solution. The novel fluxional process is thought to involve a migration of the diphosphinedigold group around the three possible edge-bridging sites on the trigonal-planar triruthenium unit, together with a concomitant movement of the edge-bridging hydride ligand. Band-shape analysis of variable-temperature 1H and 13C-{1H} NMR spectra afforded values of ΔG ‡ for these proposed metal-core rearrangements of 67.1 ± 0.2 (1H) and 67.0 ± 0.2 kJ mol–1 (13C-{1H}) for 1 and 58.9 ± 0.1 kJ mol–1 (13C-{1H}) for 2. These free energies of activation are surprisingly high compared with those previously reported for skeletal rearrangements in gold–ruthenium heteronuclear cluster compounds.