The reaction of the chloro-complex [CpRuCl(PEt(3))(2)] with acetylene gas in methanol gave the pi-alkyne complex [CpRu(eta(2)-HCtbd1;CH)(PEt(3))(2)][BPh(4)] (1), which has been structurally characterized by X-ray analysis. The alkyne complex undergoes spontaneous isomerization even at low temperature, yielding the metastable alkynyl-hydride complex [CpRu(H)(Ctbd1;CH)(PEt(3))(2)][BPh(4)] (2), as the result of the oxidative addition of the alkyne C-H bond. This compound has also been structurally characterized despite it tautomerizes spontaneously into the stable primary vinylidene [CpRu(=C=CH(2))(PEt(3))(2)][BPh(4)] (3). This species has been alternatively prepared by a two-step deprotonation/protonation synthesis from the pi-alkyne complex. Moreover, the reaction of the initial chloro-complex with monosubstituted alkynes HCtbd1;CR (R = SiMe(3), Ph, COOMe, (t)Bu) has been studied without detection of pi-alkyne intermediates. Instead of this, alkynyl-hydride complexes were obtained in good yields. They also rearrange to the corresponding substituted vinylidenes. In the case of R = SiMe(3), the isomerization takes place followed by desilylation, yielding the primary vinylidene complex. X-ray crystal structures of the vinylidene complexes [CpRu(=C=CH(2))(PEt(3))(2)][BPh(4)] (3) and [CpRu(=C=CHCOOMe)(PEt(3))(2)][BPh(4)] (10) have also been determined. Both, full ab initio and quantum mechanics/molecular mechanics (QM/MM) calculations were carried out, respectively, on the model system [CpRu(C(2)H(2))(PH(3))(2)](+) (A) and the real complex [CpRu(C(2)H(2))(PEt(3))(2)](+) (B) to analyze the steric and electronic influence of ligands on the structures and relative energies of the three C(2)H(2) isomers. QM/MM calculations have been employed to evaluate the role of the steric effects of real ligands, whereas full ab initio energy calculations on the optimized QM/MM model have allowed recovering the electronic effects of ligands. Additional pure quantum mechanics calculations on [CpRu(C(2)H(2))(PH(3))(2)](+) (C) and [CpRu(C(2)H(2))(PMe(3))(2)](+) (D) model systems have been performed to analyze in more detail the effects of different ligands. Calculations have shown that the steric effects induced by the presence of bulky substituents in phosphine ligand are responsible for experimentally observed alkyne distortion and for relative destabilization of the alkyne isomer. Moreover, increasing the phosphine basicity and sigma donor capabilities of ligands causes a relative stabilization of an alkynyl-hydride isomer. The combination of both steric and electronic effects, makes alkyne and alkynyl-hydride isomers to be close in energy, leading to the isolation of both complexes.

The reaction of propargyl alcohol derivatives with the complex [Cp*RuCl(dippe)] [dippe = 1,2‐bis(diisopropylphosphane)ethane] and NaBPh4 in MeOH yields hydrido(3‐hydroxyalkynyl) compounds [Cp*Ru(H){C≡CC(OH)RR′}(dippe)][BPh4] [R, R′ = Ph, Ph (1a); H, Ph (1b); H, Me (1c)]. These represent intermediates in the formation of 3‐hydroxyvinylidene species [Cp*Ru{=C=CHC(OH)RR′}(dippe)][BPh4] [R, R′ = Ph, Ph (2a); H, Ph (2b); H, Me (2c)], into which they irreversibly rearrange both in solution and in the solid state. Solution kinetic studies have been carried out on this isomerization process. Ulterior dehydration processes are feasible, resulting in the formation of allenylidene [Cp*Ru(=C=C=CRR′)(dippe)][BPh4] [R, R′ = Ph, Ph (3a); H, Ph (3b)] or vinylvinylidene [Cp*Ru{=C=CHCH(=CH2)}(dippe)][BPh4] (4) species. The X‐ray crystal structure of the novel secondary allenylidene complex [Cp*Ru(=C=C=CHPh)(dippe)][BPh4] is presented.

The full sequence of species involved in the activation of alkynols by the fragment [Cp*Ru(PEt3)2]+ was determined. The complex [Cp*RuCl(PEt3)2] (Cp* = C5Me5) reacts with 2-propyn-1-ol derivatives in the presence of NaBPh4, yielding the metastable 3-hydroxyalkynyl hydrido complexes [Cp*Ru(H){C⋮CC(OH)RR‘}(PEt3)2][BPh4], intermediates in the formation of the corresponding 3-hydroxyvinylidene complexes [Cp*Ru{CCHC(OH)RR‘}(PEt3)2][BPh4], to which these compounds rearrange both in solution and in the solid state. η2-Alkynol derivatives have been detected by 31P{1H} NMR at −40 °C as the first species involved in the reaction of alkynols with [Cp*Ru(N2)(PEt3)2][BPh4]. Dehydration of 3-hydroxyalkynyl hydrido and 3-hydroxyvinylidene complexes may be spontaneous or forced, leading to vinylvinylidene, allenylidene, or the novel enynyl hydrido species. The unstable allenylidene led to the formation of an alkynylphosphonio compound without an external source of phosphine.

The reactions of the allenylidene complexes [Cp*Ru{CCC(R)Ph}(dippe)][BPh4] (R = H (1), Ph (2)) with different substrates have been studied, providing a new form of allenylidene−ruthenium reactivity. The observed reactivity pattern depends strongly on the substituents on the γ-carbon. The secondary allenylidene 1 undergoes addition of weakly nucleophilic reagents such as pyrazole, 3,5-dimethylpyrazole, or thiophenol to the Cβ−Cγ double bond, yielding substituted vinylidene compounds [Cp*Ru{CCHCH(L)Ph}(dippe)][BPh4] (L = pyrazolyl (3), 3,5-dimethylpyrazolyl (4), phenylsulfanyl (5)). The reaction of 1 with pyrrole or 2-methylfuran to afford analogous complexes [Cp*Ru{CCH−CH(L)Ph}(dippe)][BF4] (L = 2-pyrrolyl (6), 5-methyl-2-furanyl (7)) takes place only in the presence of acid. This suggests that an initial protonation at the β-carbon of the allenylidene occurs, enhancing the electrophilic character of the γ-carbon atom. This mechanism involves the formation of dicationic carbyne ruthenium complexes [Cp*Ru{⋮C−CHC(R)Ph}(dippe)]2+ (R = H (8), Ph (9)), which have been isolated and characterized as [B(ArF)4] (ArF = 3,5-(CF3)2C6H3) salts, by protonation of the cationic allenylidenes with [H(Et2O)2][B(ArF)4]. The X-ray crystal structure of the carbyne compound 9 is reported. A series of neutral functionalized alkynyl compounds [Cp*Ru{C⋮CCR(L)Ph}(dippe)] (L = CH3COCH2, R = H (10), R = Ph (11); L = pyrazolyl, R = H (12); R = Ph (13)) have also been synthesized by regioselective addition of anionic nucleophiles such as potassium acetonate or potassium pyrazolate. The structures of 11 and 13 in the solid state have been determined by X-ray diffraction analysis. Protonation of 10 and 11 with HBF4·Et2O yields the vinylidene compounds [Cp*Ru{CCH−CR(CH2COCH3)Ph}(dippe)][BF4] (R = H (14), Ph (15)).