Phenylacetylene, reaction with ruthenium complexes

Ru-vinylidene complexes can be easily prepared by reaction of low-valent ruthenium complexes with terminal acetylenes. Treatment of the Ru(ii) complex 117 with phenylacetylene gave the Ru(iv)-vinylidene complex 118 in 88% yield (Scheme 41 ).60 The reaction of 118 with C02 in the presence of Et3N afforded selectively the Ru-carboxylate complex 120, probably via the terminal alkynide intermediate 119. 

The interaction of an alkyne with (tj5-C5H5)(PR3)2RuX can result in the formation of a wide variety of ruthenium complexes. The nature of the products formed depends on the conditions used and the type of alkyne reacted. Reactions between I and terminal alkynes in the presence of ammonium hexafluorophosphate lead to the formation of cationic monosubstituted ruthenium vinylidene complexes in high yield, as shown for phenylacetylene in Eq. (61) (4,67,68). 

In order to further explore the reactivity of the homobimetallic ruthenium complexes, the reaction of 4 with terminal alkynes was investigated. Thus, when phenylacetylene or ferf-butylacetylene was added to a solution of complex 4 in CH2CI2 or benzene, the rapid and quantitative formation of the corresponding rathenium- vinylidene complexes, 8 and 9, respectively, was observed (13). The formation of 8 and 9 can be rationalised by the displacement of the ethylene ligand by the respective acetylene followed by an alkyne-to-vinylidene transformation. 

Ru (Tp)(Cl)(PPh3)(MeCN)] serves as a starting material for the synthesis of new ruthenium complexes. Water was also involved in the reactions of this Ru—Tp complex with phenylacetylene and l-ethynyl-4-fluorobenzene that yields the alkenyl ketone compound [Ru(Tp)(PPh3)(C(CH2Ph)= CHC(O)Ph)] and the acyl complex [Ru(Tp)(PPh3)(C(0)CH2(C6H5)F)]. ... 

Conjugated dienes can be selectively hydrated to ketones in the presence of cationic ruthenium complexes with bipyridyl ligands. The role of ruthenium is to catalyze the isomerization of allylic alcohols formed by the addition of water to diene. This method allows one to convert butadiene to methyl ethyl ketone in high yield [187]. Hydration of triple bonds is one of the oldest catalytic processes of organic chemistry. Though this reaction has no industrial value, it can serve as a tool of fine organic synthesis. The hydration can be catalyzed by rhodium salts under phase-transfer conditions [188]. The more exotic process of the hydrolysis of phenylacetylene to toluene and carbon monoxide catalyzed by ruthenium complex should also be mentioned [189] ... 

Recently, a proposal has been put forth that a /raor-addition process may be possible through dinuclear ruthenium intermediates.34 As shown in Scheme 5, reaction of tetraruthenium aggregate A with phenylacetylene results in the fully characterized bridging dinuclear alkenyl complex B. The authors propose a direct /ra .r-dclivcry of hydride through a dinuclear intermediate may be active in the hydrosilylation catalyzed by A, though compound B itself is unreactive to Et3SiH. 

The monosubstituted vinylidene complexes are readily deprotonated with a variety of mild bases (e.g., MeO-, C032 ), and this reaction constitutes the most convenient route to ruthenium acetylide complexes. Experimentally the deprotonation is most easily achieved by passing the vinylidene complex through basic alumina. Addition of a noncomplexing acid (e.g., HPF6) to the acetylide results in the reformation of the vinylidene complex [Eq. (66)]. Reaction of 1 and terminal alkynes such as phenylacetylene in methanol followed by the addition of an excess of... 

In an extension of this work, either zinc(II), palladium(II), rhodium(I) or copper(I) salts were immobilised in an ionic liquid film (SILP, vide supra) onto diatomic earth and the catalysts tested for activity in the reaction between phenylacetylene and 4-isopropyl-phenylaminc.1 391401 The supported rhodium, ruthenium and zinc complexes afford higher rates and selectivities relative to their use under homogenous reaction conditions. Lower rates are, however, observed with the copper salt, which is rationalised by strong complexation of the ionic liquid to the Cu(I) centre. 

Water-soluble ruthenium vinylidene and allenylidene complexes were also synthetized in the reaction of [ RuC12(TPPMS)2 2] and phenylacetylene or diphenylpropargyl alcohol [29], The mononuclear Ru-vinylidene complex [RuCl2 C=C(H)Ph (TPPMS)2] and the dinuclear Ru-allylidene derivative [ RuCl( x-Cl)(C=C=CPh2)(TPPMS)2 2] both catalyzed the cross-olefin metathesis of cyclopentene with methyl acrylate to give polyunsaturated esters under mild conditions (Scheme 7.10). 

A real example following the H2-decoordination mechanism is provided by the selective hydrogenation of 1-alkynes to alkenes with the ruthenium(II) complex [(PP3)RuH(Ti2-H2)]BPh4 [PP3 = P(CH2CH2PPh2)3l [25]. A kinetic study of the hydrogenation of phenylacetylene at ambient or sub-ambient pressure showed that the reaction is first-order in catalyst concentration, second order in H2 pressure and independent of substrate concentration. At very low 1-alkyne concentration (<0.12 M), a first order dependence with respect to the substrate was observed. 

An example of this rearrangement is the reaction of the ruthenium cyclopenta-dienyl complex (ti -C5H5)RuCl(PPh3)2 with phenylacetylene to give [(q -CsHs) Ru(=C=CHPh)(PPh3)2] ". 

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