CARBONYL METAL-CLUSTERS AS HOMOGENEOUS CATALYSTS - HYDROGENATION OF ALKYNES MEDIATED BY HYDRIDOTRIRUTHENIUM CLUSTERS CONTAINING BRIDGING N-DONOR LIGANDS

The face-bridged cluster compounds [Ru-3(mu-H)(mu(3)-ampy)(CO)(9)], [Ru-3(mu(3)-ampy)(mu eta(1) eta(2)-phC=CHPh)(CO)(8)], [Ru-3(mu-H)(mu(3)-ampy)(PR(3))(Co)(8)] and [Ru3(mu 3-ampy)(mu,eta(1):eta(2)-PhC=CHph)(pph(3))(2)(Co)(6)] (Hampy = 2-amino-6-methylpyridine) are catalyst precursors for the homogeneous hydrogenation of diphenylacetylene. Stoichiometric reactions related to the catalytic processes, along with spectroscopic and kinetic studies, have demonstrated that these complexes maintain their trinuclear framework during the catalytic reactions. However, the edge-bridged cluster compound [Ru-3(mu-H)(mu-dadmb)(CO)(9)] (Hdadmb = 1,2-diamino-4,5-dimethylbenzene), which is also an efficient promoter for the homogeneous hydrogenation of diphenylacetylene, undergoes fragmentation under the catalytic conditions to give mononuclear catalytic species. In all these cases, the hydrogenation products are cis(kinetic product) and trans-stilbene (thermodynamic product) and the reactions proceed efficiently under very mild conditions (T less than or equal to 80 degrees C, P(H-2) less than or equal to 1atm). In general, alkynes insert into the hydride-ruthenium bond of hydridotriruthenium carbonyl cluster complexes containing bridging N-donor ligands to give mu eta(1):eta(2)-alkenyl derivatives. Most of these alkenyl complexes have been shown to be intermediates or catalyst precursors in/for alkyne hydrogenation reactions under homogeneous conditions.