Ruthenium 2- -hydrido

Depending on the substrate, the enallenes 213 react with a ruthenium-hydrido catalyst to give either the initial product the methylenecyclopentanes 214 with a 1,4-diene substructure or to the conjugated vinylcyclopentenes 215. The latter are formed by a subsequent ruthenium-catalyzed isomerization of the initial cycization product 214 (Scheme 15.69) [136]. 

Finally, the unusual ruthenium hydrido complex HRu(PPh3)3[HC=C(Me)C(0)0C4H9] is formed in the reaction between H2Ru(PPh3)4 and n-butylmethacrylate77). The Ru atom has oxidatively added to a vinylic C-H bond, and this compound represents the first example of such a structure. 

References to Catalytic Reactions of Ruthenium Hydrido and Related Complexes 463... 

There are relatively few examples of anionic ruthenium hydrido complexes. Thus, several papers have discussed the preparation of the [RuH6]4 ion from Ru, H2 and various lanthanide dihydrides at 800°C.2490,2491 The 99Ru Mossbauer spectra at 4.2 K for various M2[RuH6] (M = Ca, Sr, Eu, Y) are consistent with diamagnetic Ru11 centres.2492... 

Scheme 7 Reaction of ruthenium hydrido-amido complex 11 with hydrogen to give the dihydride 12 during ketone hydrogenation...

Carbon monoxide, also originating from the alcohol, inserts into the alkyl metal bond with formation of an acyl complex. By the subsequent attack of a further molecule of alcohol, the ester is released and the ruthenium hydrido complex is regenerated, thus closing the catalytic cycle. 

Recently, Grubbs and coworkers were able to isolate a ruthenium-hydrido complex, formed as a thermal degradation product of catalyst 2 which could be made responsible for double bond migration Hong, S.H., Day, M.W., Grubbs, R.H., J. Am. Chem. Soc. 2004,126 7414. 

Castro-Rodrigo R, Esteruelas MA, Fuertes S, Lopez AM, Mozo S, Onate E. Olefin-alkylidene equilibrium of 2-vinylpyridine in osmimn- and ruthenium-hydrido-tris (pyrazolybborate and osmium-cyclopentadienyl complexes. Organometallics. 2009 28 594-5951. 

The catalyst used for these mechanistic studies has been characterized by X-ray crystallography, as shown in Figure 5.6. It is obtained as a hydrido ruthenium(II) species that is also coordinated by a [BH4 anion. The catalyst is prepared by exposing the DINAP-diamine RuC12 complex to excess NaBH 54... 

It has been postulated that these cycloheptenes must be formed via a 7r-allylruthenium intermediate (Scheme 59). The cyclization is initiated by activation of the allylic C-H bond to form the 7r-allylruthenium 234. The 1-exo-dig carboruthenation of the alkynoate 234 produces the hydrido-ruthenium enolate 235. Equilibration of 235 followed by reductive elimination gives the corresponding cycloheptenes 237 and regenerates the cationic ruthenium complex. 

The most plausible mechanism proceeds through oxidative addition of the aldehyde to an active Ru(0) species to form (acyl)(hydrido)ruthenium(ll) complex 155. Insertion of the less-substituted double bond of the 1,3-diene into the Ru-H bond occurs to generate an (acyl)( 73-allyl)ruthenmm(ll) intermediate of type 156. Successive regioselective reductive eliminations between the acyl and the 73-allyl ligands provide the desired product with regeneration of the... 

The proposed mechanisms are similar in both cases and involve in particular an (aryl)(hydrido)ruthenium intermediate in which the ruthenium is additionally coordinated by an in. ( ////-generated /V-phenylimine moiety tethered to the same Ru-bound aromatic ring. The C-C bond-forming step for the construction of the corresponding heterocyclic framework proceeds via insertion of the C=N double bond into the C-Ru bond with transfer of the (hydrido) ruthenium complex to the now phenylamine nitrogen. The desired heterocycles 158 and 159 were obtained after successive reductive elimination, deamination, and dehydrogenation. 

A tentative mechanism includes ruthenium-induced isomerization of the initial allylic alcohol via (hydrido) (7T-allyl)ruthenium complex 167 to the corresponding Ru-bound enol 168. This in. ( ////-generated nucleophile complex can then add to aldehydes or imines under formation of the desired products. 

This finding is the consequence of the distribution of various ruthenium(II) hydrides in aqueous solutions as a function of pH [RuHCl(mtppms)3] is stable in acidic solutions, while under basic conditions the dominant species is [RuH2(mtppms)4] [10, 11]. A similar distribution of the Ru(II) hydrido-species as a function of the pH was observed with complexes of the related p-monosulfo-nated triphenylphosphine, ptpprns, too [116]. Nevertheless, the picture is even more complicated, since the unsaturated alcohol saturated aldehyde ratio depends also on the hydrogen pressure, and selective formation of the allylic alcohol product can be observed in acidic solutions (e.g., at pH 3) at elevated pressures of H2 (10-40 bar [117, 120]). (The effects of pH on the reaction rate of C = 0 hydrogenation were also studied in detail with the [IrCp (H20)3]2+ and [RuCpH(pta)2] catalyst precursors [118, 128].)... 

Several X-ray structural studies have been made on hydrido-ruthenium clusters (see Table... 

A number of ruthenium-based catalysts for syn-gas reactions have been probed by HP IR spectroscopy. For example, Braca and co-workers observed the presence of [Ru(CO)3l3]", [HRu3(CO)ii]" and [HRu(CO)4] in various relative amounts during the reactions of alkenes and alcohols with CO/H2 [90]. The hydrido ruthenium species were found to be active in alkene hydroformylation and hydrogenation of the resulting aldehydes, but were inactive for alcohol carbonylation. By contrast, [Ru(CO)3l3]" was active in the carbonylation of alcohols, glycols, ethers and esters and in the hydrogenation of alkenes and oxygenates. 

C10H2O11OS3, Osmium, decacarbonyl- -hydrido-/i-hydroxotri-, 34 216 CioHgN2, bpy, 2,2 -Bipyridine, 34 178, 181 CioHioRu, Ruthenium, bis(rj -cyclopenta-dienyl)-, 34 61... 

The first reported interaction between a C—H bond in a ligand and a soluble transition metal complex was that reported by Chatt and Davidson (5). The reaction product from the reaction of sodium naphthalene with (rans-dichlorodi-(dmpe)ruthenium(II) (I) (dmpe = 1,2-bisdimethylphosphinoethane) was found to be a tautomeric equilibrium mixture of the ruthenium(O) complex (II) that contains a 7r-complexed naphthalene ligand and the ruthenium(II)-hydrido complex (III) where a C(2)—H bond has added to the ruthenium ... 

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