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.
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