Alkyne scission on a trimetallic framework: Experimental evidence and theoretical analysis

Article abstract of DOI:10.1021/om00082a020

The conversion of an alkyne complex, Cp₃M₃(CO)(C₂R₂), into a dialkylidyne complex, Cp₃M₃(CR)₂, has been examined theoretically (M = Co; R = H) and experimentally (M = Rh, Ir; C₂R₂ = C₂Ph₂, C₂PhTol). The alkyne complexes have been synthesized in useful amounts via photolysis of Cp₃M₃(CO)₃ in the presence of excess alkyne. Flash vacuum pyrolysis of the alkyne complexes cleanly provides the corresponding dialkylidyne complexes. The reaction proceeds without fragmentation of the trimetallic framework and without exchange of the CR moieties. No evidence was obtained for an unsaturated alkyne complex Cp₃M₃(C₂R₂) as an intermediate. The theoretical analysis shows that such an intermediate leads to a much higher energy pathway for alkyne scission than a pathway in which the carbonyl ligand remains coordinated until the alkyne is cleaved.