Hydrido ruthenium complexes, from

The transition metal complex-catalyzed formation of 1,3-dioxepanes from vinyl ethers has also been described. For example, reaction of allyl vinyl ether 157 with a nonhydridic ruthenium complex at higher temperatures and without any solvent produced 1,3-dioxepane 159 whereas, the use of a hydridic ruthenium complex resulted in the formation of vinyl ether 158 by double-bond isomerization (Scheme 43). It was suggested that cyclic acetal formation proceeds via a 7i-allyl-hydrido transient complex, which undergoes nucleophilic attack of the OH group at the coordinated Jt-allyl <2004SL1203>. 

Catalytic transformations involving the C-H bonds of thiophene are rare, but recently there has been a report on the catalytic addition of the C(2)-H bond of thiophene across ethylene to form 2-ethylthiophene <20040M5514>. Reaction of the ruthenium complex TpRu(CO)(NCMe)(Me) (where Tp = hydrido tris(pyrazolyl)borate) with thiophene produces the 2-thienyl complex 249 and methane. This complex catalyzes the formation of 2-ethylthiophene from a solution of thiophene and ethylene (Equation 121). The mechanism of this reaction has been explored. 

An interesting synthesis of zero-valent ruthenium phosphine-trifluorophosphine complexes has been reported (2, 4) (method I) via reductive elimination of acetic acid from the ruthenium(II) hydrido acetato complex [RuH(C02Me)(PPh3)3]. 

It is noteworthy that computational and experimental studies have shown that the formation of ruthenium-vinylidenes from terminal alkynes and ruthenium hydride complexes also proceeds via the formation of t -vinyl intermediate (Scheme 8.4) [14]. Thus, in this case the vinylidene ligand is not formed directly from the alkyne, and its /3-hydrogen atom arises from the hydrido ligand. 

Reactions Involving sp -CH Activation. The insertion of ruthenium complexes into alkane C—H bonds is quite limited most synthetic routes require an adjacent nitrile group to first coordinate to the metal center. Oxidative addition of the C—H bond to the ruthenium center gives the hydrido ruthenium intermediate. An aldehyde or an a.jS-unsaturated carbonyl acts as the electrophile, which after reductive elimination from the metal affords the corresponding alcohol. This reaction is typically catalyzed by either CpRuCl(PPh3)2 or RuH2(PPh3)4 (58). 

The RCM of 1,6-dienes into cyclopentenes is sometimes accompanied by a cycloisomerisation reaction to give cyclic products with an exo-methylene substituent, especially when ruthenium-arene complexes are used as catalyst precursors (see for instance compounds 32 in Section 7.3.1.6). In many cases, this side reaction was undesired and could be effectively suppressed by the addition of various co-catalysts. It is nevertheless possible to alter the reaction path to obtain the cycloisomerisation products with very high selectivities. Early examples of NHC-Ru complexes suitable for this task included the unstable cationic alle-nylidene complexes 36 prepared in situ from more robust chelated precursors 35 (Equation (7.6)). Alternatively, a combination of IMes-HCl/Cs2C03/[RuCl2(p-cymene)]2 also provided an efficient catalytic system. A mechanism involving oxidative coupling of the 1,6-diene to a ruthenium(II) centre followed by p-elimination to generate a hydrido ruthenium(IV) intermediate and reductive elimination was proposed for the transformation (Scheme 1.9)2 ... 

Hydrogen can be generated from formic acid-amine adducts at room temperature, and used directly in fuel cells [126,127]. Ruthenium metal carbonyl and hydrido carbonyl complexes exhibit a catalytic activity in the decarboxylation of formic acid. Hence, [Ru4(CO)i2H4] prepared from RUCI3 and formic acid can decompose formic acid to hydrogen and carbon dioxide [126]. 

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 ... 

The corresponding hydrido/alkyl (and aryl) complexes v-[RuHR(L-L), ] (L-L = dppe, dppm, dmpe R = Me, Et, Ph) are readily prepared from m-[RuClR(L-L)2] and Li[AlH4]1659 whereas treatment of cis- or tvans-[RuCl2 (dmpe)2 ] with arene radical anions affords d.v-[RuH(f 1-aryl)(dmpe)2] (aryl = phenyl, 2-naphthyl, anthryl, phenanthryl).1389 In solution, these compounds are in tautomeric equilibria with significant concentrations of Ru° complexes (e.g. equation 148) although X-ray analysis for aryl = 2-naphthyl confirms the presence of the six-coordinate Ru" species (373) in the solid state.2459 Some reactions of (373) with various substrates to produce other hydrido complexes are shown in Scheme 74.44>24m Note that the compound of empirical formula [ Ru(dmpe)2 ] obtained by pyrolysis of [RuH(2-np)(dmpe)2] (reaction (iv) Scheme 74) is a binuclear Ru" hydrido complex, resulting from intermolecular oxidative addition of methyl groups to ruthenium.1390... 

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... 

Although both the brown [Os(NH3)6] and the yellow [Os(NH3)6]Br have been claimed as products of the reaction of [Os(NH3)6]Br3 with potassium in liquid ammonia,54 the products were not well characterized and could be hydrido ammines or mixtures. There is evidence from the polarographic reduction of [Os(NH3)6]3+ for the existence of [Os(NH3)6]2+ but it appears to be labile to substitution and has not been isolated 55 in this respect osmium differs significantly from ruthenium, for [Ru(NH3)6]2+ is isolable and is in fact a useful synthetic precursor. The tetravalent complex [Os(NH3)s]4+ has also been detected electrochemically, by cyclic voltammetric oxidation of [Os(NH3)6]3+ 55 in acidic solution however, the first product of one-electron oxidation of [Os(NH3)s]3+ is probably [Os(NH3)s(NH2)]3+.ss... 

---