Reduction of ruthenium

Knowledge of the active site allows for speculation on the mechanism of H2-D20 exchange which these Fe4 systems catalyze 473,483). Ruthe-nium(III) systems catalyze such an exchange via a ruthenium(III) hydride intermediate (7, p. 73 Section II,A), as exemplified in reactions (82) and (83), and iron hydrides must be involved in the hydrogenase systems. Ruthenium(III) also catalyzes the H2 reduction of ruthenium(IV) via reaction (82), followed by reaction (84) (3), and using these ruthenium systems as models, a very tentative scheme has been proposed 473) for... 

Ruvn—>RuIV) the fact that it selectively oxidizes cyclobutanol to cyclobutanone and ferf-Bu(Ph)CHOH to the corresponding ketone, militates against free-radical intermediates and is consistent with a heterolytic, two-electron oxidation [103, 104]. Presumably, the key step involved /1-hydride elimination from a high-valent, for example, alkoxyruthenium(VII), intermediate followed by reoxidation of the lower-valent ruthenium by dioxygen. However, as shown in Fig. 18, if this involved the Ru(VII)/Ru( V) couple the reoxidation would require the close proximity of two ruthenium centres, which would seem unlikely in a polymer-supported catalyst. A plausible alternative, which can occur at an isolated ruthenium centre, involves the oxidation of a second molecule of alcohol, resulting in the reduction of ruthenium(V) to ruthenium(III), followed by reoxidation of the latter to ruthenium(VII) by dioxygen (Fig. 18). 

This salt is readily formed by the reduction of ruthenium trichloride in air electrolytic cell, and immediately adding a concentrated solution... 

Potassium Chlor-ruthenite, K2RuC15.—This salt may be prepared by the reduction of ruthenium nitrosotrihydroxide, Ru(NO)(OH)3, in alkaline solution by boiling with formaldehyde, dissolving in hydrochloric acid, and separating out the salt by addition of potassium chloride.4 Obtained in this way the crystals are brown in colour. 

The preparation of the hexaammine complexes of ruthenium(II) and ruthenium (III) salts are sketchily described in the literature. The preparation of hexaammineruthenium(II) by the reduction of ruthenium trichloride with zinc in ammonia is described briefly by Lever and Powell.1 Allen and Senoff2 carry out the reduction using hydrazine hydrate. The hexaammineruthe-nium(III) cation is obtained by oxidation of the ruthenium(II) complex,1 and pentaamminechlororuthenium(III) dichloride is obtained by treating the former compound with hydrochloric acid.1,3 This compound may also be obtained by treating the pentaammine molecular nitrogen complex of ruthenium(II) with hydrochloric acid.2,4... 

Ruthenium(III) fluoride can be prepared by the reduction of ruthenium(V) fluoride with either iodine or sulfur at elevated temperatures2312 or in an impure form by reduction of [RuF5]4 with ruthenium metal.2313 It is a dark brown powder shown by X-ray powder diffraction studies to consist of RuF6 corner shared octahedra, (with Ru—Ru separations of 3.37 A).2314 Neutron diffraction studies reveal no evidence of magnetic ordering even at 4.2 K.2315... 

Some interesting conclusions can be drawn from the TPR experiments (Figure 1). First, the reduction feature of RU/AI2O3 catalyst differs from that observed for Ru/AC. Ruthenium precursors supported on carbon are reduced at lower temperatures. This fact is indicative of different metal-support interactions. Furthermore, in all the AC supported catalysts a second H2 consumption peak appears at temperatures close to 673 K. This peak is accompanied by the production of CH4, which can be originated by the partial gasification of the carbon species of the support near the metal particle [10]. Also, this peak near 673 K could indicate the presence of some Ru" species stabilized by interaction with the carbonaceous support, which would become reduced at this temperature. Moreover, the addition of MgO to the Ru/C catalyst shifts the reduction of ruthenium to higher temperatures. Thus, we can deduce that in the Ru-Mg/AC catalysts the ruthenium particles are in close interaction with the MgO. 

The Hupp group utilized electrochemical oxidation of [Ru(phen)3]2 + in the presence of tert-butyl-4-pyridine, 4-phenylpyridine, or 4,4 -bipyridine to prepare the pyridinium derivatives, (29), (30), and (31), respectively.130 It is believed that activation of coordinated (1) is facilitated by oxidation of ruthenium(II) to ruthenium(III). Subsequent elimination of an H atom from (1) by the substituted pyridines is likely accomplished by spontaneous reduction of ruthenium(III) to ruthenium(II), producing the pyridinium salt. 

Carbonylchlorohydridoruthenium complexes are often formed by the reduction of ruthenium chloride with alcohol in the presence of tertiary phosphines. The carbonyl ligand is derived from the alcohol just as Vaska s complex, lrCl(CO)(PPh3)2, is formed from (N H4)2lrCl6, PPh3 and alcohols. The carbonyl ligand is always located trans to... 

Acrylic acid formation, 61 Activation catalysis, 28 Activation energies, 112 Activation energy barrier electronic rearrangements, 99 Michaelis complex formation, 95 reduction of ruthenium, 173 Activation of CO, 131/ Activation parameters, 31... 

Polymers containing all metal backbones of Ru-Ru or Os-Os bonds have been prepared via the electrochemical reduction of ruthenium and osmium complexes containing /ram-chloride ligands.81,82 Scheme 2.6 shows the synthesis of polymers with their backbones comprised solely of metal-metal bonds. The polymers were prepared by reducing [Mn(/ran.s-Cl2)(bipyXCO)2] (M = Ru, Os), 33, to M° complexes and forming the polymer after the loss of the chloride ligands. In both cases, the polymers were selective for the reduction of carbon dioxide. 

Reductions of ruthenium carbonyls have been studied less. Reduction of Ru3(CO),2 by Na in liquid NH3 yields the [Ru(CO)4] anion, probably in admixture with [RuH(CO)4] -. Acidification of the anion with dilute H3PO4 yields the thermally unstable RuH2(CO)4. The analogous OsH2(CO)4 is a rather thermally stable compound showing that the thermal stability of the MH2(CO)4 complexes increases drastically from Fe and Ru to Os Fe = Ru Os. 

To tackle the problem outlined above and obtain information on the structure and composition of fuel cell catalysts under relevant conditions, a number of authors have proposed in situ XRD or XAS cells where samples were (1) subjected to a controlled gas atmosphere (H2, CO, etc.) at specified temperatures [17,157-160], (2) characterized in model electrochemical cells filled with liquid electrolytes [160-164], or (3) studied in operating PEMFCs and DMECs [165-169]. Both XRD [17] and XAS [158] measurements confirm that Pt and Ru oxides are reduced upon heating at 373 to 423 K in a hydrogen atmosphere. On the contrary, Roth et al. [158] have shown that in a CO atmosphere, ruthenium oxides remain relatively stable, their susceptibility to reduction depending on the Pt-to-Ru site distribution. It has been suggested that Pt in contact with Ru acts as a catalyst for the reduction of ruthenium oxides and strengthens the Ru-CO bond, favoring it over Ru-0. Reduction also occurs in electrochemical cells... 

The ruthenium catalyst (mean particle size 25 /im, Sbet = 75 m -g, mean pore size 60-70 nm) was prepared by reduction of ruthenium hydroxide, obtained by adding a sodium hydroxide solution to a ruthenium(lll)chloride solution [6,7]. 

Structural changes, accompanied with the reduction of ruthenium complexes, were extensively investigated in the case of the 2-electron reduction product of 195 (196 in Fig. 49) [174]. The X-ray structure analysis of 196 shows an unusually small distance between the quarternary carbons C-3 and C-14 the measured value of 196 pm seems to be the longest carbon single bond determined by X-ray structure analysis till now [174], The conformation of the two benzene rings is best described as similar to those found in cyclohexadienyl anions. Comparison with the spectroscopic data of other bivalent positive bis(ruthenium) complexes led to the assumption that the cyclohexadienyl anionic re-decks are present as well [174]. 

Complex 186 can be regarded as an electron reservoir compound [176] and is a suitable agent for achieving the reduction of ruthenium complexes. So 197 is reduced to the dication 198 and further on to the uncharged complex 199, where the single reduction steps are reversible (Fig. 50) [177]. 

Recently, the group of Roucoux has investigated the stabilization of Ru(0) colloids with classical methylated cyclodextrins, which are modulated by the cavity and the substitution degree (SD) [61]. The catalyticaUy active aqueous suspension of metallic Ru(0) nanoparticles was prepared by chemical reduction of ruthenium chloride with sodium borohydride in dilute aqueous solutions of methylated cyclodextrins. The TEM observations show that the average particle size is about 1.5 nm with 70% of the nanoparticles between 1 and 2.5 nm (Fig. 11.6). 

Isomerisation.—Mechanisms of isomerisation of pent-l-ene, hex-l-ene, and hept-l-ene have been discussed, with particular reference to the reduction behaviour of the respective catalysts. Thus there is an induction period for the ruthenium-trichloride-catalysed isomerisation of hex-l-ene since reduction of ruthenium trichloride to the active ruthenium(i) species is slow. There is no induction period for rhodium-trichloride-catalysed isomerisation since reduction to rhodium(i) is rapid. Isomerisation of cyclic alkenes, particularly of the cyclo-octadienes, has attracted some attention, " There has been discussion on whether the 1,4-isomer is an intermediate in the isomerisation of 1,3-cyclo-octadiene to the 1,5-isomer and vice versa the 1,4-isomer has now been detected in isomerisation of the 1,3-compound catalysed by PdCl2(benzonitrile)2 in benzene solution. Isomerisation... 

Alonso-Vante N, Bogdanoff P, Tributsch H (2(X)0) On the origin of the selectivity of oxygen reduction of ruthenium-containing electrocatalysts in methanol-containing electrolyte. J Catal 190 240-246... 

Bettelheim, A., D. Ozer, R. Harth, and R.W. Murray (1988). Redox and electrocatalytic properties towards dioxygen reduction of ruthenium tetra(orfi t)-aminophenyl)porphyrin complexes with various axial hgands. J. Electroanal. Chem. 246, 139-154. 

Nanoparticles passivated by metal-carbon double bonds have also been achieved and exemplified by ruthenium nanoparticles. The synthetic procedure is somewhat different from the biphasic route detailed. Here, ruthenium colloids are first prepared by thermolytic reduction of ruthenium chloride in 1,2-propandiol in the presence of sodium acetate. A toluene solution of diazo derivatives is then added, where the strong affinity of the diazo moiety to a fresh ruthenium surface leads to the formation of ruthenium-carbene n bonds and the concurrent release of nitrogen. The resulting particles become solnble in toluene and can be purified in a typical manner. ... 

Ru(OH)Cls] - + 3H2O + 103 where the rate-determining step is the reduction of ruthenium(iv) by the amine with rapid re-oxidation of the metal complex by the oxidant. The oxidation of iodide by isopolymolybdic acids in the presence of germaniumfiv) and phosphorus(v) has been reported, the two-stage reactions involving the formation of a Ge " (or P ") complex with the molybdate, followed by a secondary reaction of this intermediate with I to yield the blue heteropolyacid. The two-electron reaction of indium(i) with tri-iodide ions,... 

In 2005, we employed acetate stabilized ruthenium(0) nanoparticles as catalyst for the hydrolysis of SB, which is known to be the first example of nanoparticles catalyst used for this reaction [50]. Water dispersible ruthenium(0) nanoparticles are formed from the reduction of ruthenium(III) chloride in the presence of acetate anion as stabilizer. The acetate stabilized ruthenium(O) nanoparticles of 2.8 1.4nm particle size were found to be highly active catalyst in the hydrolysis of sodium borohydride even at room temperature and low catalyst concentration (Figure 7.2). The acetate stabilized ruthenium(O) nanoparticles provide 5170 TTO (total... 

Electrochemical reduction of ruthenium and osmium complexes containing /ra i-chloride ligands leads to metal-containing polymers in which metal-metal bonds make up the entire polymer backbone. Hence, reduction of [M (tran5-Cl2) (bipy)(CO)2l (M=Ru, Os) (77) to M complexes generated a polymeric film (78) after loss of the chloride ligands (Scheme 23). Both the ruthenium- and osmium-based coordination polymers were selective for the reduction of carbon dioxide to carbon monoxide and formate. 

The Ni-Ru-SDC anode is prepared by using a modified batch of SDC powder. Relatively coarse particles of SDC are mixed with ruthenium chloride to form a suspension. Following the reduction of ruthenium cation, the resulting powder is separated and dried. Figure 9.4 shows the transmission electron microscopy (TEM) images of 1 wt% (a) and 10 wt% (b) Ru-dispersed SDC particles obtained by the aforementioned preparation method. The optimum value, on the other hand, is determined in such a way that when mixed with NiO to form the anode, the concentration of ruthenium should be around 1 wt%, as estimated from the compositions of widely used precious metal catalysts [15]. 

The reduction of ruthenium to the metal proceeds without difficulty in mineral acid media. Griess (208) has applied this process to the determination of ruthenium in 0.3 m hydrochloric or sulphuric acids by deposition into platinum cathodes at potentials of —0.35 V vs. NHE. In a very significant paper, Page and Wilkinson (209) reported the reduction of ruthenocene in an ethanolic perchlorate solution to yield insoluble ruthenicinium perchlorate in a one-electron step at a potential of 0.26 V vs. SCE. 

---