Homogeneous hydrogenation of diphenylacetylene in the presence of Ru₃(CO)₉L₃ (L=PPh₃, PEt₃). The crystal structure of Ru₃(CO)₁₀(PEt₃)₂: A reaction intermediate?

The phosphine-substituted clusters Ru₃(CO)₉L₃ (L=PPh₃, 1; L=PEt₃, 2) are active homogeneous catalysts for the hydrogenation of diphenylacetylene. In the catalytic reactions involving complex 2, formation of Ru₃(CO)₁₀(PEt₃)₂ (3) has been observed. This complex shows a hydrogenating activity greater than that of the parent complex 2. In the light of these results and of the observed effect of dihydrogen pressure and substrate/cluster ratio, reaction mechanisms are discussed. The structure of 3 has been characterized by X-ray diffraction and is compared with those of other phosphine-substituted triruthenium clusters. Compound 3 crystallizes in the monoclinic space group P2₁ with a=9.368(7), b=12.20(2), c=13.554(9) Å, β=102.63(8)° and Z=2. Refinement of 4975 data gave R₁=0.0417 and wR₂=0.1105. The two phosphorus ligands occupy equatorial positions on adjacent metal atoms so that they are trans to each other at the ends of the Ru-Ru vector. The presence of bent semi-bridging carbonyl groups makes the molecule chiral and its absolute structure was determined.