Methylidyne-Alkyne Coupling on Triruthenium Clusters and Hydrogenation of Cluster-Bound 1, 3-Dimetalloallyl Units. A New Model for Fischer-Tropsch Chain Growth

Alkylidyne-alkyne coupling occurs upon reaction of H₃ru₃(μ₃-CX)(CO)₉(X = OMe, Me, Ph, or CH₂CH₂CMe₃) at 25 °C or hru₃(μ-cx)(co)₁₀(X = OMe) at 60 °C with alkynes R¹C₂R², forming 1, 3-dimetalloallyl clusters HRu₃(_^μ3-η³-XCCRCR)(CO)₉(X = OMe, (R¹, R²) = (H, H), (Me, Me), (Ph, Ph), (H, Ph), (H, CMe₃), (H, n-Bu), (H, CO₂Me), (Ph, CO₂Me), (H, OEt); X = Ph, (R¹, R²) = (Ph, Ph); X = Me, (R¹, R²) = (Me, Me); X = CH₂CH₂CMe₃, (R¹, R²) = (Ph, Ph)) in yields of 15-90%. In an analogous fashion, HOs₃(μ-COMe)(CO)₁₀and PhC₂Ph yield HOs₃(μ₃-η³-MeOCCPhCPh)(CO)₉. One equivalent of the appropriate cis-alkene is formed from reduction of alkyne by H₃Ru₃(μ₃-CX)(CO)₉. With unsymmetrical alkynes the relative amounts of the two possible regioisomers depend upon the alkyne substituents. Coupling from either H₃R₃(μ₃-COMe)(CO)₉or HRu₃(μ-COMe)(CO)₁₀forms HRu₃(μ₃-η³-MeOCCR¹CR²)(CO)₉in the relative amounts (R¹, R²) = (H, Ph)/(Ph, H), 3:1, (H, n-Bu)/(rc-Bu, H), 2:1, (H, CMe₃)/(CMe₃, H), 20:1, (H, CO₂Me)/(CO₂Me, H), 2:1, (H, OEt)/(OEt, H), 1:0, (Me, C₇H₁₅)/(C₇H₁₅, Me), 3:1, and (CO₂Me, Ph)/(Ph, CO₂Me), 2:1. Hydrogenation (90 °C, 1–4 atm) of HRu₃(μ₃-η³-MeOCCR¹CR²)(CO)₉((R¹, R²) = (H, H), (H, CMe₃), (Me, Me), (Ph, Ph), (H, OEt), (H, Ph), (H, n-Bu), (n-Bu, H), (H, CO₂Me)) produces in each case the corresponding H₃ru₃(μ₃-CCHR¹CH₂R²)(CO)₉in yields of 6-43%; also formed are substantial quantities of H₄Ru₄(CO)₁₂. Hydrogenation of DRu₃(μ₃-η³-MeOCCHCCMe₃)(CO)₉produces exclusively H₃RU₃U₃-CCH₂CHDCMe₃)(CO)₉. This alkylidyne-alkyne coupling and subsequent hydrogenation to form an alkylidyne of longer carbon chain length suggests a mechanism to account for 2-methylated hydrocarbon products in the Fischer-Tropsch reaction.