Ruthenium Allenylidene/Alkenylcarbyne Complexes Triggering Keto−Enol Tautomerism: An Alternative Approach to γ-Keto Vinylidenes from Simple Ketones and 1,3-Dicarbonyl Compounds

[Cp*Ru(=C=C=CHPh)(dippe)][BP 4 ] and [Cp*Ru(≡C-C=CHPh)(dippe)][BF 4 ] 2 complexes are reactive toward a variety of simple ketones (acetone, acetophenone, cyclopentanone) and 1,3-dicarbonyl compounds (acetylacetone, dimethylmalonate, malononitrile, ethyl acetoacetate) to give a series of alkylated vinylidene compounds [Cp*Ru{=C=CH-CH(L)Ph}(dippe)][BF4] (dippe = l,2-bis(diisopropylphosphino)ethane). Two cross-linked processes are operating simultaneously, creating two interconverting pairs of species: the allenylidene/carbyne complexes and the keto/enol tautomers of the ketones, producing the final vinylidene product, which is stable due to the formation of a new C-C bond. The protonation/ deprotonation equilibrium produces the electrophilic alkenylcarbyne complex and enols as the nucleophilic reagent. Stoichiometric studies with deuterated reagents and NMR monitoring of the reaction have been carried out. The X-ray structure of [Cp*Ru{=C=CH-CH(CH2COCH3)Ph}(dippe)][BF4] is also reported.