Reaction of a heterobimetallic polyhydrido cluster, [Cp*Ru(μ-H) 4OsCp*] (Cp* = η5-C5Me 5), with diphenylacetylene. Regioselective C-H bond activation at the osmium center

Article abstract of DOI:10.1021/om700606q

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-frans-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:n²-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-C₆H ₄-)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 [(C₅Me ₄Et)Ru(μ-H)₂(μ-trans-PhHC=CHPh)OsCp*] (80′, [(C₅Me₄Et)Ru(μ-H)(μ-η¹: η²-cis-PhC=CHPh)(oros-Ph HC=CHPh)OsCp*] (11′), 12, [Cp*Os(μ-PhC= CH-C ₆H₄-)H₂Ru(C₅Me₄Et)] (13′), and [Cp*Os(μ-PhC=CH-C₆H₄-)H ₂OsCp*] (15) are determined by X-ray studies.