Ruthenium complexes, reactions anionic species

Similarities between [Ru(bpy),]2+ (discussed in Chapter 13) and [Pt,(pop)J4 are apparent. Reactive excited states are produced in each when it is subjected to visible light. The excited state ruthenium cation, [Ru(bpy)3]" +, can catalytically convert water to hydrogen and oxygen. The excited slate platinum anion, [Pt,(pop)J 4-, can catalytically convert secondary alcohols to hydrogen and ketones. An important difference, however, is that the ruthenium excited stale species results from (he transfer of an electron from the metal to a bpy ligand, while in the platinum excited state species the two unpaired electrons are metal centered. As a consequence, platinum reactions can occur by inner sphere mechanisms (an axial coordination site is available), a mode of reaction rot readily available to the 18-clectron ruthenium complex.-03... 

Although this spectrum does not correspond to any particular ruthenium carbonyl complex, it is consistent with the presence of one or more anionic ruthenium carbonyl complexes, perhaps along with neutral species. Work is in progress with a variable path-length, high pressure infrared cell designed by Prof. A. King, to provide better characterization of species actually present under reaction conditions. 

Reactions between salts of [m Jo-7-CBioHi3] and [Fc3(CO)i2] afford the mononuclear anionic iron compound [2,2,2-(CO)3-c/o5o-2,l-FeCBioHn], typically isolated as its [N(PPh3)2] salt (11) (Chart 4). No anionic triiron complex analogous to 5 and 7 is formed in this reaction. The anionic mononuclear iron, ruthenium and osmium complexes and the previously mentioned neutral mononuclear ruthenium dicarbollide complex 4, obtained from [Ru3(CO)i2] and /Jo-7,8-C2BgHi3, are iso-lobal with the cyclopentadienide species [Mn(CO)3(ri-C5H5)] and [Fe(CO)3 (il-CsHs)]. ... 

Scheme 10.14 rationalizes the divergent behavior of the two catalytic systems in these selective transformations of pent-l-yn-ols. The presence of phosphine ligands promotes the formation of ruthenium vinylidene species which are key intermediates in both reactions. The more electron-rich (p-MeOC6Fl4)3P phosphine favors the formation of a cyclic oxacarbene complex which leads to the lactone after attack of the N-hydroxysuccinimide anion on the carbenic carbon. In contrast, the more labile electron-poor (p-FC6H4)3P) phosphine is exchanged with the N-hydroxysuccinimide anion and makes possible the formation of an anionic ruthenium intermediate which liberates the cyclic enol ether after protonation. 

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... 

Laine (43-47) used potassium hydroxide to promote the catalytic activity of [Ru3(CO),2] and [H4Ru4(CO),2] for the hydroformylation of pent-1-ene. Under 64 bar of CO pressure, at 135 or 150°C, high selectivities for straight-chain aldehydes were obtained, for example, 97%. As the subsequent reduction of aldehydes to alcohols is lower, important aldol condensations occurred owing to the presence of a base in solution. Analysis of the reaction mixtures has shown that the anionic [H3Ru4(CO),2] cluster is likely to be the active species. Since this complex was recognized as the major component of the low pressure ruthenium-catalyzed water gas shift... 

---