Aquo-ruthenium complex

The ring-opening metathesis polymerization (ROMP) of functionalized olefins can be catalyzed by ruthenium aquo complexes and proceeds best in aqueous solution (Scheme 22). The formation of olefin complexes [Ru(H20)5(olefin)] ... 

These mechanisms are reflected in the pH-dependence of the redox potentials in Figure 3. This approach has been used to elucidate the redox mechanisms of a wide variety of ruthenium-aquo complexes, " " as well as aquo complexes of other metals. ... 

Ruthenium(II) bipyridyl and Cr(III) aquo complexes luminesce strongly when photostimulated. The emission of light can be quenched effectively by such species as oxygen, paraquat, Fe(II) aquo complexes, Ru(II) complexes and Cr(NCS)i (Sutin [15]). Pfeil [16] found that the quenching rate coefficients are typically a third to a half of the value which might be predicted from the Smoluchowski theory [3]. 

Presumably the entire ruthenium(II)-amine-S02 series also contains the ly -pla-nar geometry. These complexes are very stable to atmospheric oxygen and thermal loss of SO2 in the solid state. However, in aqueous solution, [Rua(NH3)4(S02)] is rapidly converted to an aquo complex, followed by SO2 hydrolysis to form coordinated bisulfite or sulfite depending upon pH ... 

Many ruthenium nitrosyl complexes are well characterized and appear to act as NO+ carriers. For example the bipyridyl complex [Ru(bipy)2(NO)Cl] + reacts with azide ion to give the aquo complex, nitrogen and nitrous oxide... 

Ruthenium complexes are excellent reagents for protein modification and electron-transfer studies. Ru +-aquo complexes readily react with surface His residues on proteins to form stable derivatives [20, 21]. Low-spin pseudo-octahedral Ru-complexes exhibit small structural changes upon redox cycling between the Ru + and Ru + formal oxidation states [3, 22]. Hence, the inner-sphere barriers to electron transfer (Ai) are small. With the appropriate choice of ligand, the Ru + + reduction potential can be varied from <0.0 to >1.5 V versus NHE [23]. Ru-bpy complexes bound to Lys and Cys residues have been employed to great advantage in studies of protein-protein ET reactions. The kinetics of electron transfer in cytochrome 65/cytochrome c [24], cytochrome c/cytochrome c peroxidase [12], and cytochrome c/cytochrome c oxidase [25] complexes have been measured with the aid of laser-initiated ET from a Ru-bpy label. 

Ruthenium(II) ammine complexes can be readily prepared under mild conditions by reacting the aquo complex with neutral ligand followed by air oxidation ... 

Preliminary results of the reaction between vanadium(iii)-tetrasulpho-phthalocyanine complex with oxygen have been reported these data were compared with those obtained for the corresponding reaction of the hexa-aquo complex ion. The oxidation of methyl ethyl ketone by oxygen in the presence of Mn"-phenanthroline complexes has been studied Mn " complexes were detected as intermediates in the reaction and the enolic form of the ketone hydroperoxide decomposed in a free-radical mechanism. In the oxidation of 1,3,5-trimethylcyclohexane, transition-metal [Cu", Co", Ni", and Fe"] laurates act as catalysts and whereas in the absence of these complexes there is pronounced hydroperoxide formation, this falls to a low stationary concentration in the presence of these species, the assumption being made that a metal-hydroperoxide complex is the initiator in the radical reaction. In the case of nickel, the presence of such hydroperoxides is considered to stabilise the Ni"02 complex. Ruthenium(i) chloride complexes in dimethylacetamide are active hydrogenation catalysts for olefinic substrates but in the presence of oxygen, the metal ion is oxidised to ruthenium(m), the reaction proceeding stoicheiometrically. Rhodium(i) carbonyl halides have also been shown to catalyse the oxidation of carbon monoxide to carbon dioxide under acidic conditions ... 

The diimine ligands 2-(phenylazo)pyridine and its p-methyl derivative [(33) R = H or Me] form bis complexes [Ru(LL)2XY]" with ruthenium(II). The complexes with X = Y = Cl, Br, or I (n = 0) react with tertiary phosphines by a second-order process with /c2 values apparently controlled by the bulk of the entering ligand. The complexes with X = py, Y = OH2, and X = Y = OH2 n = 2) react quite quickly with donor solvents such as acetronitrile or dimethyl sulfoxide the bis-aquo complex also reacts rapidly with pyridine. Complexes d5-[Ru(LL)2X2], when LL = an aryl-azooxime [(34) with R = aryl], readily lose HX on addition of a base such... 

Hydrosoluble iridium alkyl complexes may also be prepared by hydrolysis of alkynes and alkenes promoted by water-soluble precursors. The reaction with alkynes follows the well-known mechanism demonstrated by Bianchini et al. for ruthenium complexes.A reasonable mechanism, related to that of hydrolytic breakage, has been proposed by Chin etal. to account for the hydrolysis of ethene promoted by [Cp"lr(TPPMS)Cl2] 344 in the presence of silver salts in water. Scheme 37 describes the Chin s hydrolysis of alkynes, leading to [Cp Ir(TPPMS)(CO)(CH2R)] (69 R=Ph, Bz, Bu, />-Tol) via the aquo complex [Cp Ir(TPPMS)(OH2)OTf 345... 

These hydroxo-salts are all sulphur-yellow crystalline substances. The acid residues are hydrolysable and hence outside the co-ordination complex, and the aqueous solutions, unlike the hydroxo-salts of chromium-and cobalt-ammines, are neutral to litmus, a fact which Werner suggests is due to the smaller tendency of the hydroxo-radicle attached to ruthenium to combine with hydrogen ions. This tendency is much less than in the case of the ammines of cobalt and chromium, but that it still exists is indicated by the increased solubility of these hydroxo-compounds in water acidified with mineral acids, and from such solutions aquo-nitroso-tetrammino-ruthenium salts are obtained thus ... 

Aquo-ruthenium salts, therefore, cannot be washed with alcohol or water, as both reagents cause hydrolysis. They may, however, be washed with absolute ether or with acetone without causing any change. Like all aquo-ammino-metallic salts, these compounds may be caused to lose water, passing thereby into aeido-tetrammino-salts, where one acidic radicle enters the complex thus ... 

Anhydrous ruthenium(lll) chloride, RuCL, is made by direct chlorination of the metal at 700°C. Two aliotropic forms result. The trihydrate is made by evaporating an HQ solution of rulheinuiu(III) hydroxide to dryness or reducing ruthenium(VIII) oxide in a HQ solution. The tnhydrate, RuCk 3R>0, is the usual commercial form. Aqueous solutions of the tri-hydrate are a straw color in dilute solution and red-brown in concentrated solution. Ruthenium(lll) chloride in solution apparently forms a variety of aquo- and hydroxy complexes. The analogous bromide. RuBr3, is made by the same solution techniques as the chloride, using HBr instead of HQ. 

More recently, Taqui Khan and co-workers (70) introduced the potentially tetradentate ethylenediaminetetraacetate ligand in the ruthenium coordination sphere in order to obtain an efficient water-soluble catalyst precursor. Indeed, starting from the ruthenium(III) aquo EDTA species [Ru(EDTA)(H20)] , carbonylation gives the paramagnetic carbonyl complex [Ru(EDTA)(CO)] which is able to induce the heterolytic activation of dihydrogen (Scheme 3). The hydroformylation of hex-l-ene performed at 50 bar (CO/H2= 1/1) and 130°C in a 80/20 ethanol-water solvent... 

The importance of hydroxycarbonyl intermediates is well illustrated in a recent study of the stepwise oxidation of CO to CO2 by binuclear ruthenium complexes". Deprotonation of a diruthenium(I) aquo species yields a hydroxy intermediate which rearranges to an isolable hydroxycarbonyl complex, equation (h). Deprotonation of the hydroxycarbonyl with NEts in dichloromethane results in a formally diruthenium(O) ii-CO complex, equation (i). 

Ruthenium(III) and osmium(III) complexes are all octahedral and low-spin with 1 unpaired electron. Iron(III) complexes, on the other hand, may be high or low spin, and even though an octahedral stereochemistry is the most common, a number of other geometries are also found. In other respects, however there is a gradation down the triad, with Ru occupying an intermediate position between Fe and Os . For iron the oxidation state +3 is one of its two most common and for it there is an extensive, simple, cationic chemistry (though the aquo... 

---