Ruthenium hydrido complex anion

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... 

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... 

The mechanism of the hydrogenation of a,j -unsaturated carboxylic acids by chiral ruthenium BINAP complexes has been investigated (Scheme 5). The rate-limiting step in methanol at near-ambient temperature is the activation of H2 to give a anionic hydrido complex. The reaction is sensitive to strong acids one equivalent CF3SO3H per Ru prevents catalysis, while base has no effect. Over 90% enantiomeric excess (ee) was achieved. ... 

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... 

The same kind of observation was made recently by D. Dombeck [31] of Union Carbide for the same reaction using ruthenium clusters. In the case of ruthenium there is, under catalytic conditions, evidence for the presence of [HRu3(CO)ii] HRu(CO)4 and Ru(CO)3lJ. An almost complete catalytic cycle has been established by Dombeck. It appears that the hydrido anionic cluster [HRu3(CO)ii]" or HRu(CO)7 make a nucleophilic attack at CO coordinated to the mononuclear carbonyl Ru(II) complex to give a formyl species. The reaction, here, would obey a very complex mechanism involving both mononuclear and polynuclear species. This phenomenon seems to be a general rule in many reactions involving CO. 

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