Alkyne-Acetylide Coupling in Cluster Compounds Bearing a Triosmium Carbonyl Os₃(CO)₈ Fragment and a High Oxidation State (C₅Me₅)W(O)₂ Unit

Treatment of acetylide cluster Cp*WOs₃(μ-O)₂(μ-CCPh)(CO)₉ (1), Cp* = C₅Me₅, with diphenylacetylene affords two cluster complexes Cp*W(O)Os₃(μ-O)(CCPh)(PhC₂Ph)(CO)₈ (2) and Cp*W(O)Os ₃(μ-O)(CCPhCPhCPh)(CO)₈ (3a) by alkyne coordination and cluster-assisted formation of C-C bonds between acetylide and alkyne, respectively. For the reaction with phenylacetylene, only the coupled product Cp*W(O)Os₃(μ-O)(CCPhCHCPh)(CO)₈ (3b) is obtained, together with a small amount of Cp*W(O)Os ₃(μ-O)(CCPhCCHPh)(CO)₈ (4). Complex 2 slowly converts to 3a and the complex Cp*W(O)(μ-O)Os₃(CCPhCPhCPh)(CO)₈ (5a) when heated in toluene, whereas the formation of 4 is believed to pass through a pathway involving an alkyne-to-vinylidene rearrangement. The conversion from complexes 3 to 5 demonstrates a unique skeletal isomerization involving the interchange of a Cp*W(O)₂ unit and one Os(CO)₃ fragment.