Allenylidene/Alkenylcarbyne Synthesis and Reactivity in Ruthenium Complexes with Monodentate Phosphine Ligands

An alternative reactivity mode of electron-rich allenylidene complexes via alkenylcarbyne species is reported for the first time in ruthenium complexes bearing monodentate phosphine ligands (triethylphosphine). Allenylidene complexes have been prepared and characterized from [Cp*RuCl(PEt₃)₂] and a series of propargyl alcohols bearing different substituents (HCCCRR′(OH), where R, R′ = Ph, Ph; R = H, R′ = p-MeO-C₆H₄, C₆H₅, p-F-C₆H₄). Alkenylcarbyne complexes are prepared by protonation of the allenylidene precursors. The X-ray structures of one secondary allenylidene (R, R′ = H, Ph) and one alkenylcarbyne complex (R, R′ = Ph, Ph) constitute the first examples for ruthenium complexes bearing monodentate phosphine ligands. Neutral alkynyl, cationic γ-substituted vinylidene, and bicyclic carbene complexes have been isolated and characterized as a result of the allenylidene/alkenylcarbyne reactivity against anionic and neutral (protic and aprotic) nucleophiles. The cycloaddition products obtained by double addition of 1,3-cyclohexanedione and resorcinol (benzene-1,3-diol) to both allenylidene double bonds and the analysis of the effects of including electron-donor or -withdrawing groups in the allenylidene/alkenylcarbyne reactivity are reported.