Ruthenium colloidal

Fig.3 NMR spectra (d -THF, 101 MHz) ofCi6H33NH2 stabilized ruthenium colloid (a), C16H33NH2 stabilized ruthenium colloid + excess C16H33NH2 (b), (c), (d), C16H33NH2 (e)...

Several ruthenium systems catalyze the hydrogenation of aromatic rings, and this topic is detailed in Chapter 16. An early example reported by Bennett and coworkers was that of RuHCl( 76-C6Me6)(PPh3), which catalyzed the hydrogenation of benzene to cyclohexane at 25 °C, 1 bar H2 [69]. Since ruthenium colloids are very active for this reaction under certain conditions, there is evidence that at least some of the reported catalysts are heterogeneous [70]. 

More recently, Chung introduced a combination of a well-designed GO surrogate 30 and ruthenium colloidal particles (RuCNC) (Equation (12)). =... 

The liquid phase hydrogenation of benzene on carrier-fixed ruthenium colloid catalysts suspended in an aqueous solution of sodium hydroxide proceeds with 59% cyclohexene selectivity at 50% benzene conversion. The catalysts are prepared by adsorbing a hydrophilic stabilized ruthenium metal colloid on lanthanum oxide. Protection of metal colloids with chiral molecules can lead to a new type of enan-tioselective catalyst combining good selectivity control with extraordinarily high activity in hydrogenation reactions. This concept has been applied for the first time in the form of platinum sols stabilized by the alkaloid dihydrocinchonidinel °°l (Fig. 7). 

In the same way, ruthenium colloidal systems prepared by reduction of RuCh under dihydrogen in the presence of trioctylamine allowed reduction of various substituted aromatics [27]. They studied the stereo- and chemo-selectivities of the hydrogenation of aromatics in a methanol-water system at 50 bar of H2 and at room temperature. The results obtained are presented in Table 11.5. Reaction time to reach 100% conversion depends on the electronic and steric properties of the substituents on the aromatic ring, more electron-rich substrates giving rise to a favored reaction. 

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. ... 

Kim H, Chun H, Kim G-K, Lee H-S, Kim K. Ruthenium nanoparticles inside porous [Zn Ofbdc) ] by hydrogenolysis of adsorbed [Ru(cod)(cot)] a solid-state reference system for surfactant-stabihzed ruthenium colloids. Chem Commun 2006 2759-61. 

This technique is the most widely used and the most useful for the characterization of molecular species in solution. Nowadays, it is also one of the most powerful techniques for solids characterizations. Solid state NMR techniques have been used for the characterization of platinum particles and CO coordination to palladium. Bradley extended it to solution C NMR studies on nanoparticles covered with C-enriched carbon monoxide [47]. In the case of ruthenium (a metal giving rise to a very small Knight shift) and for very small particles, the presence of terminal and bridging CO could be ascertained [47]. In the case of platinum and palladium colloids, indirect evidence for CO coordination was obtained by spin saturation transfer experiments [47]. 

Sathish Kumar P, Manivel A, Anandan S, Zhou M, Grieser F, Ashokkumar M (2010) Sonochemical synthesis and characterization of gold-ruthenium bimetallic nanoparticles. Colloids Surf A 356 140-144... 

Bulk techniques still have a place in the search for presolar components. Although they cannot identify the presolar grain directly, they can measure anomalous isotopic compositions, which can then be used as a tracer for separation procedures to identify the carrier. There are several isotopically anomalous components whose carriers have not been identified. For example, an anomalous chromium component enriched in 54Cr appears in acid residues of the most primitive chondrites. The carrier is soluble in hydrochloric acid and goes with the colloidal fraction of the residue, which means it is likely to be submicron in size (Podosck el al., 1997). Measurements of molybdenum and ruthenium in bulk primitive meteorites and leachates from primitive chondrites show isotopic anomalies that can be attributed to the -process on the one hand and to the r- and /7-processes on the other. The s-process anomalies in molybdenum and ruthenium correlate with one another, while the r- and /7-process anomalies do not. The amounts of -process molybdenum and ruthenium are consistent with their being carried in presolar silicon carbide, but they are released from bulk samples with treatments that should not dissolve that mineral. Thus, additional carriers of s-, r-, and/ -process elements are suggested (Dauphas et al., 2002). 

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