Carbon-Hydrogen Bond Activation by Triruthenium Carbonyl Species during Carbon Monoxide Promoted Elimination of 4,5-Dihydroacenaphthylene from [(μ₂: η¹: η⁵-C₁₂H₁₀)Ru₃H ₂(CO)₇]: Implication of Reaction Intermediates

Oxidative addition of a vinylic C-H bond occurred during the CO-promoted elimination of 4,5-dihydroacenaphthylene (3) from [(μ₂ : η¹ : η⁵-C₁₂H₁₀)Ru₃H ₂(CO)₇] (2) in CH₂Cl₂. The product, [(μ₃ : η¹ : η² : η²-C₁₂H₉)Ru₃H(CO)₉] (4), was isolated and characterized by spectroscopy and crystallography. The carbonylation of a deuterium-labelled complex, [(μ₂ : η¹ : η⁵-C₁₂H₈D₂)Ru₃D ₂(CO)₇] (2-d₄), under the same conditions as that from 2 to 3 in CH₂Cl₂ afforded 4,5-dideuterioacenaphthylene (3-d₂) and [(μ₃ : η¹ : η² : η²-C₁₂H₇D₂)Ru ₃H(CO)₉] (4-d₂). The lack of incorporation of deuterium atoms into the ruthenium hydride in 4-d₂ suggested that dissociation of D₂ from the triruthenium moiety in 2-d₄ induced the oxidative addition of the vinylic C-H bond. Further carbonylation of 4 did not occur under the same conditions as the reaction from 2 to 4, but gave 3 in moderate yields under higher CO pressure (8 atm) at 50 - 100 °C. These results suggest that 4 was not directly involved in the CO promoted elimination of 3 from 2, but was closely related to the actual intermediates. Possible reaction mechanisms are discussed.