Efficient One-Pot Synthesis of α<i>,</i>β-Unsaturated Carbyne Complexes <i>f</i><i>ac</i>-[RuX₃{⋮CC(H)CR₂}(dppf)] (X = Cl, Br; R = Aryl, Alkyl; dppf = 1,1‘-Bis(diphenylphosphino)ferrocene)

Alkenyl-carbyne complexes fac-[RuX3{⋮CC(H)CR2}(dppf)] (X = Cl, Br; R = Ph, iPr or CR2 = C13H8) (2a−c, 3a−c) have been prepared by reaction of the bis(allyl)-ruthenium(II) derivative [Ru(η3-2-C3H4Me)2(dppf)] (1) with the appropriate propargylic alcohol HC⋮CCR2(OH) in the presence of 3.5 equiv of the corresponding hydrogen halide HX. The structure of compounds fac-[RuCl3{⋮CC(H)CR2}(dppf)] (R = Ph (2a) and iPr (2c)) has been confirmed by X-ray crystallography. Structural parameters within the alkenyl-carbyne chain in 2a,c suggest an important contribution of the zwitterionic vinylidene canonical form fac-[RuCl3{CC(H)-CR2}(dppf)]. Formation of complexes 2,3a−c involves the 1,3-addition of HX to the corresponding dinuclear allenylidene intermediates [{RuX(μ-X)(CCCR2)(dppf)}2]. Such allenylidene complexes, i.e., [{RuX(μ-X)(CCCR2)(dppf)}2] (X = Cl, Br; R = Ph or CR2 = C13H8) (4a,b, 5a,b), have been prepared and characterized by treatment of fac-[RuX3{⋮CC(H)CR2}(dppf)] (X = Cl, Br; R = Ph or CR2 = C13H8) (2a,b, 3a,b) with 1 equiv of AgSbF6, via halide abstraction and concomitant deprotonation of the alkenyl-carbyne chain.