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)][BF4] and [Cp*Ru(⋮C−CCHPh)(dippe)][BF4]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 = 1,2-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.