Reactivity of methylidyne ligands on trinuclear clusters of group 8 metals

The chemistry of alkylidyne containing clusters HM₃(μ-CX)(CO)₁₀ and H₃M₃(μ₃-CX)(CO)₉ is presented-(1) structures, bonding and spectroscopic characterizations, (2) syntheses involving modification of the methylidyne substituent, (3) alkyne-alkylidyne coupling, and (4) formation of HCX bonds. Reactions of HRu₃ (COMe)(CO)₁₀ or H₃Ru₃(CX)(CO)₉ (X = OMe, Ph or alkyl) with alkynes, produce HRu₃(μ₃-η³-XCCRCR)(CO)₉ clusters containing 1,3-dimetalloallyl ligands. Hydrogenation of these products when X = OMe or SEt gives new alkylidynes H₃Ru₃(μ₃-CCHRCH₂R)(CO)₉. For X = SEt, isomerization of HRu₃(μ₃-η³-EtSCCRCR)(CO)₉ to Ru₃(μ-SEt)(μ₃-η³-CCRCHR)(CO)₉, a presumed intermediate in the hydrogenation reaction, occurs under mild conditions. Under CO, reductive elimination of CH₃X can be induced from H₃Ru₃(μ₃-CX)(CO)₉ (X = OMe, Ph, Cl or CO₂Me). Pyrolysis of H₃Ru₃(μ₃-CX)(CO)₉, X = CO₂Me and SEt, gives stabilized intermediates H₂Ru₃(μ₃-CHCO₂Me) (CO)₉ and HRu₃(μ₃-CH₂SEt)(CO)₉, respectively. Protonation of H₃Ru₃(μ₃-CR)(CO)₉ (R = Et or CHPhCH₂Ph) yields H₃Ru₃(μ₃-HCR)(CO)₉¹⁺, in which the alkylidene hydrogen is agostic; the protonated clusters undergo more rapid reductive elimination than the neutral precursors. The kinetics and mechanism of reductive elimination have been investigated. A mechanism is presented.