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)], [R u-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 mpy)(mu,eta(1):eta(2)-PhC=CHph)(pph(3 ))(2)(Co)(6)] (Hampy = 2-amino-6-methylpyridine) are catalyst precurso rs for the homogeneous hydrogenation of diphenylacetylene. Stoichiomet ric reactions related to the catalytic processes, along with spectrosc opic and kinetic studies, have demonstrated that these complexes maint ain their trinuclear framework during the catalytic reactions. However , the edge-bridged cluster compound [Ru-3(mu-H)(mu-dadmb)(CO)(9)] (Hda dmb = 1,2-diamino-4,5-dimethylbenzene), which is also an efficient pro moter for the homogeneous hydrogenation of diphenylacetylene, undergoe s fragmentation under the catalytic conditions to give mononuclear cat alytic species. In all these cases, the hydrogenation products are cis (kinetic product) and trans-stilbene (thermodynamic product) and the r eactions proceed efficiently under very mild conditions (T less than o r equal to 80 degrees C, P(H-2) less than or equal to 1atm). In genera l, alkynes insert into the hydride-ruthenium bond of hydridotrirutheni um carbonyl cluster complexes containing bridging N-donor ligands to g ive mu eta(1):eta(2)-alkenyl derivatives. Most of these alkenyl comple xes have been shown to be intermediates or catalyst precursors in/for alkyne hydrogenation reactions under homogeneous conditions.