Reaction of a Heterobimetallic Polyhydrido Cluster, [Cp*Ru(μ-H)4OsCp*] (Cp* = η5-C5Me5), with Diphenylacetylene. Regioselective C−H Bond Activation at the Osmium Center

The reactivity of a heterobimetallic polyhydrido complex [Cp*Ru(μ-H)4OsCp*] (1) toward diphenylacetylene is studied to elucidate the roles of each metal atom in the substrate activation step. The reaction of 1 with an equivalent of diphenylacetylene exclusively produces a η2-trans-stilbene complex [Cp*Ru(μ-H)2(μ-trans-PhHCCHPh)OsCp*] (8), in which trans-stilbene is coordinated to the osmium metal by way of the η2-cis-stilbene complex [Cp*Ru(μ-H)2(μ-cis-PhHCCHPh)OsCp*] (10). Treatment of 1 with an excess amount of diphenylacetylene yields [Cp*Ru(μ-H)(μ-η1:η2-cis-PhCCHPh)(trans-PhHCC HPh)OsCp*] (11) via complex 8. Intermediacy of 8 in the formation of 11 is confirmed by the reaction of 8 with diphenylacetylene. Thermolysis of 11 in C6D6 at 50 °C generates a μ-perpendicularly coordinated diphenylacetylene complex [Cp*Ru(μ-H)2(μ-η2:η2-PhCCPh)OsCp*] (12) and a benzo-osmacyclopentadiene complex [Cp*Os(μ-PhCCH−C6H4−)H2RuCp*] (13) together with trans-stilbene. Complex 8 is converted into 13 even in the absence of added diphenylacetylene. Upon heating of 8 in THF, 13 is formed as a result of the C(sp2)−H bond cleavage and subsequent intramolecular activation of the C(ortho)−H bond at the osmium center. The molecular structures of [(C5Me4Et)Ru(μ-H)2(μ-trans-PhHCCHPh)OsCp*] (8‘), [(C5Me4Et)Ru(μ-H)(μ-η1:η2-cis-PhCCHPh)(trans-Ph HCCHPh)OsCp*] (11‘), 12, [Cp*Os(μ-PhCCH−C6H4−)H2Ru(C5Me4Et)] (13‘), and [Cp*Os(μ-PhCCH−C6H4−)H2OsCp*] (15) are determined by X-ray studies.