Ruthenium activity

A significant step was made by neutron irradiation of ruthenocene. It was found that 20—25% of the ruthenium activity was recoverable as ruthenocene, and that also considerable rhodium activity was sublimed along with the ruthenocene. The rhodium was identified as being rhodium dicyclopentadienide, produced in high yield by the decay of ruthenocene. 

Activation of vinyl C-H bonds with RuH2(CO)(PPh3)3 catalyst has allowed the formal insertion of a,/l-unsaturated ketones or esters into the C-H bond of vinylsilanes and led to a regioselective C-C coupling at the -position [9] (Eq. 6). Activation of the sp2 C-H bond occurred with the aid of chelation of a coordinating functional group and provided vinylruthenium hydride 14. Insertion of olefin afforded the tetrasubstituted alkene 13. The ruthenium activation of a variety of inert C-H bonds has now been performed by Murai [10]. 

As mentioned above, there are several computational investigations that indicate that the addition of adsorbed hydrogen atoms to CO lowers the overall activation energy for CO dissociation. Ciobica and van Santen (5) demonstrated that on the (0001) terrace of ruthenium, activation of CO through a formyl intermediate would proceed with a barrier of 140 kj/mol. This value is substantially lower than the barrier of 210 kJ/ mol that was found for direct CO dissociation on the same surface. However, on stepped surfaces, the pathway via association with H atoms was found not to be competitive with direct CO dissociation. 

The intramolecular addition of a hydroxy group to a triple bond has been performed successfully in the presence of RuCl2(PPh3)(p-cymene) as catalyst precursor under mild conditions [18, 19]. The Lewis acid property of the ruthenium active species provides the activation of the triple bond and the Markovnikov addition of the hydroxy group to form 2-methylfuran derivatives after 1,5-proton shift and aromatiza-tion (Scheme 8.8). 

The addition of carbonucleophiles to alkynes promoted by ruthenium complexes is not documented. However, several examples of C-H bond addition to alkynes with C-C bond formation have been performed. These involve the ruthenium activation of a C-H bond of aromatic ketones [117, 118] such as 2-methylacetophenone, tetra-lone [119[ (Scheme 8.42), and enones [120, 121]. 

Whereas the catalytic hydrosilylation of alkynes was one of the first methods of controlled reduction and functionalization of alkynes, the ruthenium-catalyzed hydroamination of alkynes has emerged only recently, but represents a potential for the selective access to amines and nitrogen-containing heterocydes. It is also noteworthy that, in parallel, the ruthenium activation of inert C-H bonds allowing alkyne insertion and C-C bond formation also represents innovative aspects that warrant future development. Among catalytic additions to alkynes for the production of useful products, the next decade will clearly witness an increasing role for ruthenium-vinylidenes in activation processes, and also for the development of ruthenium-catalyzed hydroamination and C-H bond activation. 

In dioxane, when X = O or RN, the reaction proceeds smoothly. However, when a methyl group is introduced into the olefmic moiety, the reaction is suppressed. On the other hand, in DMAC the introduction of a methyl group to the olefmic moiety does not affect the catalytic activity, though when X = O or RN, a deallylation reaction proceeds to disturb the cyclization reaction. In DMAC, oxidative addition of the allyl-X group to the ruthenium active species would occur, most likely due to the coordination of a more electron-donating amide solvent. Thus, the two reports are mutually supportive. 

Salts of [Ru(CO)4] or [H2Ru4(CO),2] can also conveniently be used. These dianionic complexes can be directly generated by mixing [Ru3(CO),2] or [H4Ru4(CO),2] with another dianionic compound such as [Na2Fe(CO)4] or [Na2W2(CO),o] (30,31). The addition of a second metal complex also seems to provide a stabilization of the ruthenium active species since, for instance, in 3 hours a selectivity of 91% has been maintained for a conversion of 68% of pent-l-ene. Moreover, addition of [Co2(CO)g] to the dianionic complex (PPN)2(H2Ru4(CO),2] (molar ratio 1/1) increases the reactivity and the stability of the system. In fact 31% of oct-l-ene is converted in 1 hour to w-nonanal with 97% selectivity. 

Tfie concentration of plutonium in combined core and blanket fuel from the LMFBR is more than 10 times that of LWR fuel. This is the most significant difference between the two fuels with respect to reprocessing. Other important differences are the greater amounts of tritium and the 140 percent greater ruthenium activity, and the 60 percent greater overall specific activity of ISO-day cooled LMFBR fuel. 

Guerrero-Ruiz et al. [139] have studied the catalytic behaviour of ruthenium for the conversion of -hexane when supported on non-reducible carriers such as activated carbon and high-surface-area graphite. The samples were also characterized by microcalorimetry of CO adsorption. The higher initial heat of CO adsorption observed for ruthenium/graphite (135 kJ mol ) compared to ruthenium/activated carbon (115 kJ mol ) indicates an enhanced electron density of the ruthenium particles caused by electron transfer from the graphite. The catalytic results show that ruthenium particles with an increased electron density have a higher activity for -hexane conversion. 

Another most recent and successful example concerns the ring-expansion metathesis polymerization (REMP) of cycloolefins using cyclic carbene-ruthenium complex. " In this reaction, the cyclic olefin coordinates onto the ruthenium active center before insertion into the cyclic carbene ring. 

The proposed mechanism (Scheme 3.76) starts with the oxidative cyclization of diyne XLII on the Cp RuCl fragment, followed by coordination of 208 and formal [2 -1- 2] coupling. Subsequent Ru—C cleavage and reductive elimination afford the desired product 209 and regenerate the ruthenium active species. The complete regioselectivity observed in the insertion of alkyne 208 can be explained in... 

A choline amperometric biosensor based on screen-printed configuration, immobilized by adsorption from aqueous solution on the surface of ruthenium-activated carbon electrodes, was assembled and used to assess the inhibitory effect of organophosphoms and carbamic pesticides on acetylcholinesterase activity both... 

A ruthenium catalyst is particularly active for promoting this reaction. Organic compounds can also be reduced with hydrogen ... 

Ion implantation has also been used for the creation of novel catalyticaHy active materials. Ruthenium oxide is used as an electrode for chlorine production because of its superior corrosion resistance. Platinum was implanted in mthenium oxide and the performance of the catalyst tested with respect to the oxidation of formic acid and methanol (fuel ceU reactions) (131). The implantation of platinum produced of which a catalyticaHy active electrode, the performance of which is superior to both pure and smooth platinum. It also has good long-term stabiHty. The most interesting finding, however, is the complete inactivity of the electrode for the methanol oxidation. 

Ruthenium. Ruthenium, as a hydroformylation catalyst (14), has an activity signiftcandy lower than that of rhodium and even cobalt (22). Monomeric mthenium carbonyl triphenylphosphine species (23) yield only modest normal to branched regioselectivities under relatively forcing conditions. For example, after 22 hours at 120°C, 10 MPa (1450 psi) of carbon monoxide and hydrogen, biscarbonyltristriphenylphosphine mthenium [61647-76-5] ... 

Imidazole is characterized mainly by the T) (N) coordination mode, where N is the nitrogen atom of the pyridine type. The rare coordination modes are T) - (jt-) realized in the ruthenium complexes, I-ti (C,N)- in organoruthenium and organoosmium chemistry. Imidazolium salts and stable 1,3-disubsti-tuted imidazol-2-ylidenes give a vast group of mono-, bis-, and tris-carbene complexes characterized by stability and prominent catalytic activity. Benzimidazole follows the same trends. Biimidazoles and bibenzimidazoles are ligands as the neutral molecules, mono- and dianions. A variety of the coordination situations is, therefore, broad, but there are practically no deviations from the expected classical trends for the mono-, di-, and polynuclear A -complexes. 

Rapoport s findings have been confirmed in the authors laboratory where the actions of carbon-supported catalysts (5% metal) derived from ruthenium, rhodium, palladium, osmium, iridium, and platinum, on pyridine, have been examined. At atmospheric pressure, at the boiling point of pyridine, and at a pyridine-to-catalyst ratio of 8 1, only palladium was active in bringing about the formation of 2,2 -bipyridine. It w as also found that different preparations of palladium-on-carbon varied widely in efficiency (yield 0.05-0.39 gm of 2,2 -bipyridine per gram of catalyst), but the factors responsible for this variation are not knowm. Palladium-on-alumina was found to be inferior to the carbon-supported preparations and gave only traces of bipyridine,... 

Ruthenium is excellent for hydrogenation of aliphatic carbonyl compounds (92), and it, as well as nickel, is used industrially for conversion of glucose to sorbitol (14,15,29,75,100). Nickel usually requires vigorous conditions unless large amounts of catalyst are used (11,20,27,37,60), or the catalyst is very active, such as W-6 Raney nickel (6). Copper chromite is always used at elevated temperatures and pressures and may be useful if aromatic-ring saturation is to be avoided. Rhodium has given excellent results under mild conditions when other catalysts have failed (4,5,66). It is useful in reduction of aliphatic carbonyls in molecules susceptible to hydrogenolysis. 

Anilines have been reduced successfully over a variety of supported and unsupported metals, including palladium, platinum, rhodium, ruthenium, iridium, (54), cobalt, and nickel. Base metals require high temperatures and pressures (7d), whereas noble metals can be used under much milder conditions. Currently, preferred catalysts in both laboratory or industrial practice are rhodium at lower pressures and ruthenium at higher pressures, for both display high activity and relatively little tendency toward either coupling or hydrogenolysis,... 

Both amine oxides related to pyridines and aliphatic amine oxides (/25) are easily reduced, the former the more so. Pyridine N-oxide has been reduced over palladium, platinum, rhodium, and ruthenium. The most active was rhodium, but it was nonselective, reducing the ring as well. Palladium is usually the preferred catalyst for this type of reduction and is used by most workers 16,23,84 158) platinum is also effective 100,166,169). Katritzky and Monrol - ) examined carefully the selectivity of reduction over palladium of a... 

Ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [PBuJBr was reported by Knifton as early as in 1987 [2]. The author described a stabilization of the active ruthenium-carbonyl complex by the ionic medium. An increased catalyst lifetime at low synthesis gas pressures and higher temperatures was observed. 

Hydrogenation of olefinic unsaturation using ruthenium (Ru) catalyst is well known. It has been widely used for NBR hydrogenation. Various complexes of Ru has been developed as a practical alternative of Rh complexes since the cost of Ru is one-thirtieth of Rh. However, they are slightly inferior in activity and selectivity when compared with Rh catalyst. 

Table 5 lists other ruthenium complexes that could catalyze selective hydrogenation in NBR. However, their activity could not be properly compared as they... 

The structure of the aqua complex (Figure 1.51), which is an active intermediate in some catalytic systems, shows the Ru-OH2 distance to be some 0.1 A longer than in the ruthenium(III) hexaqua ion, indicating a possible reason for its lability the water molecule also lies in a fairly exposed position, away from the bulk of the EDTA group. 

The first catalytic study of Reaction 1 was published in 1902 by Sabatier and Senderens (1) who reported that nickel was an excellent catalyst. Since that time, the active catalysts were identified as the transition elements with unfilled 3d, 4d, and 5d orbitals iron, cobalt, nickel, ruthenium, rhenium, palladium, osmium, indium, and platinum, as well as some elements that can assume these configurations (e.g., silver). These are discussed later. For practical operation of this process,... 

Catalysts. The methanation of CO and C02 is catalyzed by metals of Group VIII, by molybdenum (Group VI), and by silver (Group I). These catalysts were identified by Fischer, Tropsch, and Dilthey (18) who studied the methanation properties of various metals at temperatures up to 800°C. They found that methanation activity varied with the metal as follows ruthenium > iridium > rhodium > nickel > cobalt > osmium > platinum > iron > molybdenum > palladium > silver. 

The most successful class of active ingredient for both oxidation and reduction is that of the noble metals silver, gold, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum and palladium readily oxidize carbon monoxide, all the hydrocarbons except methane, and the partially oxygenated organic compounds such as aldehydes and alcohols. Under reducing conditions, platinum can convert NO to N2 and to NH3. Platinum and palladium are used in small quantities as promoters for less active base metal oxide catalysts. Platinum is also a candidate for simultaneous oxidation and reduction when the oxidant/re-ductant ratio is within 1% of stoichiometry. The other four elements of the platinum family are in short supply. Ruthenium produces the least NH3 concentration in NO reduction in comparison with other catalysts, but it forms volatile toxic oxides. 

There is little data available to quantify these factors. The loss of catalyst surface area with high temperatures is well-known (136). One hundred hours of dry heat at 900°C are usually sufficient to reduce alumina surface area from 120 to 40 m2/g. Platinum crystallites can grow from 30 A to 600 A in diameter, and metal surface area declines from 20 m2/g to 1 m2/g. Crystal growth and microstructure changes are thermodynamically favored (137). Alumina can react with copper oxide and nickel oxide to form aluminates, with great loss of surface area and catalytic activity. The loss of metals by carbonyl formation and the loss of ruthenium by oxide formation have been mentioned before. 

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