Reactivity of the Tetrametallic Carbido Cluster (C₅Me₅)WOs₃(μ₄-C)(μ-H)(CO)₁₁ with Alkyne: Isomerization of an Allyl Fragment on a Tetrametallic Cluster Framework and Ring-Methyl Activation in the C₅Me₅ Ligand

Treatment of the tetrametallic carbido—benzofuryl cluster (C₅Me₅)WOs₃(μ₄-C)(μ-H)₂(μ-C₈H₆O)(CO)₉ (1) with pressurized CO gas affords a carbido cluster (C₅Me₅)WOs₃(μ ₄-C)(μ-H)(CO)₁₁ (2) in nearly quantitative yield. The reactions of 2 with diisopropyl acetylene-dicarboxylate (DPAD) are investigated. If complex 2 is first treated with Me₃NO, the incorporation of DPAD at room temperature affords a cluster compound (C₅Me₅)-WOs₃(CO)₁₀[C₃H(CO₂Prⁱ)₂] (3) in moderate yield, in which the allyl group is formed by hydride migration to the carbide. Complex 3 undergoes a facile metathesis to yield an isomer (4) with a different arrangement of the allyl C₃ backbone. Upon thermolysis, complex 4 converts to a η⁶-tetramethylfulvene complex [C₅Me₄(CH₂)]WOs₃(μ-H)[C₃H(CO₂Prⁱ)₂](CO)₉ (5) by activation of a ring-methyl in the C₅Me₅ ligand and a trialkylidyne cluster (C₅Me₅)WOs₃(μ₃-CH)(μ₃-CCO₂Prⁱ)₂(CO)₉ (6) by cleavage of two allyl C—C bonds. The possible mechanism of their interconversion is discussed. If the reaction of the Me₃NO-activated complex 2 and DPAD is carried out in refluxing toluene, we obtained one more compound (C₅Me₅)-WOs₃[CC₂(CO₂Prⁱ)₂H](CO)₁₀ (7) in low yield, which appears to form through a secondary process involving hydride migration to the DPAD molecule instead.