Reactions of allene with triosmium and triruthenium clusters including coupling and oxidative addition: X-ray structure of the coupled allene compound [Os3(C6H8)(CO)10]

Abstract

Allene (CH₂CCH₂) reacts with [Os₃(CO)₁₁(MeCN)] to give the known compound [Os₃(µ-C₃H₄)(CO)₁₁] and with [Os₃(CO)₁₀(MeCN)₂] to give [Os₃(µ₃-C₆H₈)(CO)₁₀], the single-crystal X-ray structure of which shows an open chain of metal atoms [Os–Os–Os 136.8(1)°] with the C₆H₈ ligand, formed by end-to-centre allene coupling, bridging three Os atoms through µ,η²-vinyl and η³-allyl linkages. U.v. photolysis of [Os₃(µ-C₃H₄)(CO)₁₁] gives mainly [Os₃H(µ₃-σ,η²,η²-CHCCH₂)(CO)₉] which isomerises thermally to [Os₃H(µ₃-σ,σ,η³-CHCHCH)(CO)₉]. In contrast, thermolysis of [Os(µ-C₃H₄)(CO)₁₁] gives mainly [Os₂(µ-σ,η³-C₃H₄)(CO)₇](92%; reaction under CO). Thus photolysis leads to Os–CO and C–H cleavages and thermolysis to Os–Os cleavages. Reaction of [Ru₃(CO)₁₁(MeCN)]with allene at 0 °C gives [Ru₂(µ,σ,η³-C₃H₄)(CO)₇] with no evidence for trinuclear products. Tetramethylallene reacts slowly with [Os₃(CO)₁₁(MeCN)]to give [Os₃(C₃Me₄)(CO)₁₀] of unknown structure.