Acetylene complexes with ruthenium

Reaction of acetylenic complexes with triosmium dodecacarbonyl leads to a variety of products involving one, two, or three acetylenic units. As with ruthenium, for the monosubstituted alkynes, hydrogen transfer can occur to the metal cluster. Thus, Os3(CO)12 and phenyl-acetylene (L) yield, in refluxing benzene, the derivatives Os3(CO)10L, Os3(CO)10L2, Os3(CO)9L, and HOs3(CO)9(L-H). The general chemistry is summarized in Scheme 2 (131). 

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. 

This observation may well explain the considerable difference between metal-olefin and metal-acetylene chemistry observed for the trinuclear metal carbonyl compounds of this group. As with iron, ruthenium and osmium have an extensive and rich chemistry, with acetylenic complexes involving in many instances polymerization reactions, and, as noted above for both ruthenium and osmium trinuclear carbonyl derivatives, olefin addition normally occurs with interaction at one olefin center. The main metal-ligand framework is often the same for both acetylene and olefin adducts, and differs in that, for the olefin complexes, two metal-hydrogen bonds are formed by transfer of hydrogen from the olefin. The steric requirements of these two edgebridging hydrogen atoms appear to be considerable and may reduce the tendency for the addition of the second olefin molecule to the metal cluster unit and hence restrict the equivalent chemistry to that observed for the acetylene derivatives. 

Consiglio and Morandini and co-workers (67) have investigated the stereochemistry involved in the addition of acetylenes to chiral ruthenium complexes. Reaction of propyne with the separated epimer of the chiral ruthenium phosphine complex 34 at room temperature results in the chemo- and stereospecific formation of the respective propylidene complex 64. An X-ray structure of the product (64) proves that the reaction proceeds with retention of configuration at the ruthenium center. The identical reaction utilizing the epimer with the opposite configuration at ruthenium (35) also proceeded with retention of configuration at the metal center, proving that the stereospecificity of the reaction in not under thermodynamic control [Eq. (62)]. 

Dixneuf suggested that this reaction proceeds via the nucleophilic attack of a carbamate anion to the ruthenium vinylidene intermediate generated by the reaction of ruthenium complexes with terminal acetylene. The details of this reaction are discussed in Chapter 8. 

The reaction between acetylenes and ruthenium carbonyls produces a series of n complexes with cyclic ligands which, as in the iron system, have either the metal or a CO group incorporated into the ring. Accordingly, 3-hexyne 536) and hexafluoro-2-butyne 90) react with Ru3(CO)i2 to give the (substituted cyclopentadienone)tricarbonylruthenium complexes with structures presumably comparable to those of the iron complexes (93-95). Although diphenylacetylene will not react directly with Ru3(CO)i2 to produce this type of complex 536), it can be prepared 90) by treating Ru3(CO)i2 with tetracyclone in benzene under reflux. 

Recent literature describes the synthesis of vinyl esters in the presence of platinum metal complexes. Complexes which have proven particularly suitable in this context are those of ruthenium (eq. (15)), such as, for example, cyclooc-tadienylruthenium halides [36], ruthenium carbonyl complexes, and ruthenium acetate complexes [37]. A characteristic feature of these is their high selectivity with regard to acetylene, so that the production of acetylene polymers is reduced. 

The first anti-Markovnikov hydration of terminal acetylenes, catalyzed by ruthenium(II)-phosphine complexes, has been described in 1998 [27], As shown on Scheme 9.8, the major products were aldehydes, accompanied by some ketone and alcohol. In addition to TPPTS, the fluorinated phosphine, PPh QFs) also formed catalytically active Ru-complexes in reaction with [ RuC12(C6H6) 2]. 

Acetylenic compounds form adducts with acrylic acid derivatives, catalysed by a ruthenium complex with 1,5-cyclooctadiene (cod) and 1,3,5-cyclooctatriene (cot), as shown in reaction 10. ... 

Acetylenic silyl ethers can be transformed catalytically into synthetically useful conjugated dienol silyl ethers by treatment with ruthenium hydride complexes at 150 C in sealed tubes/ ... 

Complex formation with flic substrate is the key stage of many catalytic processes. The formation of the following types of organometallic complexes is most typical in catalysis alkyl 7i-complexes, carbene complexes, n-complexes of substrates with the saturated bond (olefin, acetylene and allyl, complexes with carbon oxides), hydrazine complexes, and complexes with molecular oxygen and nitrogen. The structure of a ruthenium complex with CO2 obtained on the basis of an ab initio study is presented in Fig. 17.4. 

Other transition-metals have also been used. For example, Trost183 reported that heating a 1 1 mixture of 1-octene and 1-octyne in DMF-water (3 1) at 100°C with a ruthenium complex for 2 h generated a 1 1 mixture of two products corresponding to the addition of the alkene to the acetylene (Eq. 3.47). The presence of a normally reactive enolate does not interfere with the reaction. 

A series of novel ruthenium(IV) dioxolene complexes, formally [3 + 2] cycloadducts, have been obtained via the reaction of cix-[Ru (0)2(Me3tacn)(CF3C02)] with trimethylsilylacetylenes (Scheme 14). " These dark blue complexes display a characteristic UV-vis absorption band at 550-680 nm. They are also characterized by electrospray mass spectrometry. The X-ray structure of the complex formed with bis(trimethylsilyl)acetylene has been determined the two Ru—O bonds of the metallocycle are of the same length (1.978 A). 

Numerous investigations have been undertaken on the reactions of ruthenium carbonyls with olefins and acetylenes. Two complex types [55] and [56] result from the reaction of Ru3(CO)j2 with ethylene and other Simple olefins (127). The complexes [56], which belong to the products of reaction (1) (Chapter 2.5.) are also formed from Ru3(CO)i2 and diphenyl acetylene (183). [55] and [56] show interesting fluxional properties, and four different types of ligand scrambling are possible (163). 

Two (cyclopentadienyl)bis(phosphine)ruthenium chloride complexes have been investigated the nonlinearities are low. These results have been used in conjunction with measured nonlinearities of acetylenes and acetylide complexes to demonstrate that values for the latter are not simply the sum of the molecular components (see earlier). An example of a metal... 

Sterically hindered systems - As already pointed out in Sect. 3.2, the sterically hindered ruthenium tetramesitylporphyrins Ru(TMP) or Ru(TMP)L2 (L = MeCN, N2,THF) [204,154] are useful starting materials for the synthesis of or-ganometallic compounds [209, 316]. While the reaction of Ru(N2)2(TMP) with acetylene yielded a divinylidene bridged complex, (TMP)Ru=CH-CH = Ru-(TMP), 1 1 rc-complexes were formed with phenylaacetylene, diphenyl-acetylene, ethylene, or cyclohexene [209]. Ru(CH2 = CH2)(TMP) was deposited solvent-free by evaporation from benezene and precipitated with 2-propanol as a diliganded solvate, Ru(CH2 = CH2)(TMP) i-PrOH i-PrOH. The compounds were characterized by elemental analyses and H and 13C NMR spectra. 

The regioselective anti-Markovnikov addition of benzoic acid to phenyl-acetylene has also been carried out with success at 111 °C in the presence of ruthenium complexes containing a tris(pyrazolyl)borate (Tp) ligand [RuCl(Tp)(cod), RuCl(Tp)(pyridine), RuCl(Tp)(N,N,Ar,AT-tetramethylethyl-enediamine )] with a stereoselectivity in favour of the (E)-enol ester isomer [22]. The o-enynyl complex Ru(Tp)[PhC=C(Ph)C=CPh](PMe/-Pr2) (C) efficiently catalyses the regioselective cyclization of a,cu-alkynoic acids to give en-docyclic enol lactones [23] (Eq. 2). 

The addition of substituted alkenes with electron-withdrawing groups to ruthenium acetylide complexes results in the formal [2 + 2] cycloaddition of the olefin to the acetylene moiety. Facile ring opening of the resultant ruthenium cyclobutene complex (103) generates the ruthenium butadienyl species (104). Subsequent displacement of a phosphine ligand leads to the Tj3-allylic product (105) [Eq. (93)] (90-92). The intermediate cyclobutene complex has been isolated in one instance for the monocarbonyl derivative 106 [Eq. (94)] (92). 

Pericyclic reactions involving thiophenes have been utilized to prepare a variety of complex heterocycles. The intramolecular Diels-Alder reaction of 2-vinylbenzo[i]thiophene 92 produced a pair of tetracyclic adducts 93 and 94 <02TL3963>. Coupling of Fischer carbene 96 with 3-alkynylthiophene 95 led to the formation of thieno[2,3-c]pyran-3-one 97 in one step <02JOC4177>. An intramolecular cycloaddition of 97 then afforded tetracyclic adduct 98. A ruthenium-catalyzed cyclodimerization reaction involving bis-thienyl acetylene derivatives was... 

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