Ruthenium on silica

Selective hydrogenation of a diketone. 4-Hydroxycyclohexanone has not been obtained in satisfactory yield by selective hydrogenation of 1,4-cyclohexanedione under homogeneous conditions. However it can be obtained in 70% yield by hydrogenation of the dione in 2-propanol with 5% ruthenium on silica. Some other metals (platinum, iridium) are more reactive, but less selective. 

MC Shoenmaker-Stolk, JW Verwijs, JA Don, JJF Scholten. The catalytic hydrogenation of benzene over supported metal catalysts. 1. Gas-phase hydrogenation of benzene over ruthenium-on-silica. Appl Catal 29 73-90, 1987. 

Ammonia decomposition was investigated by Choudhary et al. [283] over nickel, iridium and ruthenium catalysts supported by various carrier materials such as ZSM-5 and Y-zeolites, alumina and silica. Ruthenium on silica was most active, followed by iridium and nickel [283]. 

Chloro-2-(3-methyl-4H-1,2,4-triazol-4-yDbenzophenone (Oxidation of 7solution prepared by adding sodium periodate (2 g) to a stirred suspension of ruthenium dioxide (200 mg) in water (35 ml). The mixture became dark. Additional sodium periodate 18 g) was added during the next 15 minutes. The ice-bath was removed and the mixture was stirred for 45 minutes. Additional sodium periodate (4 g) was added and the mixture was stirred at ambient temperature for 18 hours and filtered. The solid was washed with acetone and the combined filtrate was concentrated in vacuo. The residue was suspended in water and extracted with methylene chloride. The extract was dried over anhydrous potassium carbonate and concentrated. The residue was chromatographed on silica... 

The copper EXAFS of the ruthenium-copper clusters might be expected to differ substantially from the copper EXAFS of a copper on silica catalyst, since the copper atoms have very different environments. This expectation is indeed borne out by experiment, as shown in Figure 2 by the plots of the function K x(K) vs. K at 100 K for the extended fine structure beyond the copper K edge for the ruthenium-copper catalyst and a copper on silica reference catalyst ( ). The difference is also evident from the Fourier transforms and first coordination shell inverse transforms in the middle and right-hand sections of Figure 2. The inverse transforms were taken over the range of distances 1.7 to 3.1A to isolate the contribution to EXAFS arising from the first coordination shell of metal atoms about a copper absorber atom. This shell consists of copper atoms alone in the copper catalyst and of both copper and ruthenium atoms in the ruthenium-copper catalyst. 

Other metals on silica supports have been investigated less extensively than platinum and nickel, and average particle diameters have only been estimated by gas adsorption methods, supported in a few cases by X-ray line broadening data. Thus, rhodium, iridium, osmium, and ruthenium (44, 45) and palladium (46) have all been prepared with average metal particle diameters <40 A or so, after hydrogen reduction at 400°-500°C. 

In a somewhat different approach, supported-aqueous-phase-catalysts (SAPC, see Chapter 5, Section 5.2.5 of this book) have been combined with supercritical CO2 in catalytic hydrogenation [55], Ruthenium was supported on silica and combined with the ligand TPPTS in water, after which a scC02/H2 phase was applied together with the substrate. Better levels of conversion were obtained using scC02 than the equivalent system with toluene for the hydrogenation of cinnamaldehyde. 

The SULPHOS-containing rhodium and ruthenium complexes retained their catalytic activity in heteroarene hydrogenation when supported on styrene-divinylbenzene polymer [180] or on silica [181], and showed even higher activity than in homogeneous solution. This effect is attributed to the diminished possibility of dimerization of the active catalytic species to an inactive dimer on the surface of the support relative to the solution phase. The strong hydrogen bonds between the surface OH-groups on silica and the -SO3 substituent in 31 withheld the catalyst in the solid phase despite the rather drastic conditions (100 °C, 30 bar H2). 

As commented previously, alkenyl(amino)allenylidene ruthenium(II) complexes 41 are easily accessible through the reaction of indenyl-Ru(ll) precursors with ynamines (Scheme 10) [52-54]. Based on this reactivity, an original synthetic route to polyunsaturated allenylidene species could be developed (Scheme 19) [52, 53]. Thus, after the first ynamine insertion, complex 41 could be transformed into the secondary derivative 62 by treatment with LiBHEts and subsequent purification on silica-gel column. Complex 62 is able to insert a second ynamine molecule, via the cyclization/cycloreversion pathway discussed above, to generate the corresponding dienyl(amino)allenylidene species. Further transformations of this intermediate in the presence of LiBHEts and Si02... 

An interesting application of TSIL was developed by Zhang et al for the catalytic hydrogenation of carbon dioxide to make formic acid. Ruthenium immobilized on silica was dispersed in aqueous IL solution for the reaction. H2 and CO2 were reacted to produce formic acid in high yield and selectivity. The catalyst could easily be separated from the reaction mixture by filtration and the reaction products and the IL were separated by simple distillation. The TSIL developed for this reaction system was basic with a tertiary amino group (N(CH3)2) on the cation l-(A,A-dimethylaminoethyl)-2,3-dimethylimidazolium trifluoromethanesulfonate, [mammim] [TfO]. 

Olefin metathesis has become a very important reaction in polymer chemistry and natural product synthesis [47-49]. Garber et al. have used the physical properties of dendrimers in order to improve the separation between the dendritic metathesis catalyst and products on silica gel column chromatography [50]. The Van Koten group has reported on the synthesis of different generations of carbosilane dendrimers functionalized with ruthenium metathesis catalysts [51]. 

Figure 5.61 Schematic representation of a [Ru(bpy)3]2+/a-ZrP viologen structure on silica, plus the sequence of fast (1,2) and slow (3) electron transfer steps that follow photoexcitation of the photoactive ruthenium-containing polymer MDESA, p-methoxyaniline diethylsulfonate. Reprinted from Coord. Chem. Rev., 185-186, D. M. Kaschak, S. A. Johnson, C. C. Waraksa, J. Pogue and T. E. Mallouk, Artificial photosynthesis in lamellar assemblies of metal poly(pyridyl) complexes and metalloporphyrins, 403-416, Copyright (1999), with permission from Elsevier Science...

The adsorption and subsequent reaction of ethylene on Group VIII metal surfaces provides a rich chemistry, which depends upon the adsorption temperature and the Group VIII metal. 13c NMR offers great potential to investigate the adsorbed states and to follow the reaction of ethylene on the surface. The study of the reactions of ethylene on Ru surfaces by 13c NMR has been reported by Gerstein and coworkers.(7,2) They have shown that ethylene on silica-supported ruthenium is converted to ethane, n-butane, 2- butenes and strongly adsorbed alkyl groups. 

Ru-1,4,7-trimethyl-1,4,7-triazocyclononane complexes ds-[Ru(l,4,7-trimethyl-l,4,7-triazacyclononane)(02)(CF3C02)]+ with ferf-BuOOH [20,21] also afforded reasonable results and recently this complex was heterogenized on silica [50]. In contrast to the homogeneous catalyst, this heterogeneous ruthenium complex in epoxidation of cyclohexene produced cyclohexene oxide in 75% yield with cyclohexen-l-one in 14% yield, while the homogeneous catalyst produced cyclohexen-l-ol and cyclohexen-l-one mainly. Examples of... 

A benzene solution of diphenyl ditellurium and trisftetracarbonylruthenium] heated at 60" for four hours formed bis[tricarbonylbenzenetellurolatoruthenium] and oligomeric di-carbonylbis[benzenetellurolato]ruthenium. The reaction mixture was chromatographed on silica gel to separate these compounds1. 

The reactions are catalyzed by transition metals (cobalt, iron, and ruthenium) on high-surface-area silica, alumina, or zeolite supports. However, the exact chemical identity of the catalysts is unknown, and their characterization presents challenges as these transformations are carried out under very harsh reaction conditions. Typically, the Fischer-Tropsch process is operated in the temperature range of 150°C-300°C and in the pressure range of one to several tens of atmospheres [66], Thus, the entire process is costly and inefficient and even produces waste [67]. Hence, development of more economical and sustainable strategies for the gas-to-liquid conversion of methane is highly desirable. 

Platinum, ruthenium, and mixed platinum-ruthenium species supported on silica Various alumina-supported nickel complexes Dispersion of metallic species during treatments in 02 and H2 at temperatures up to 473 K Reaction of nickel complexes and interaction with support at temperatures... 

In a different type of reaction, alkenes are photooxygenated (with singlet O2, see 14-7) in the presence of a Ti, V, or Mo complex to give epoxy alcohols, such as 180, formally derived from allylic hydroxylation followed by epoxidation. " In other cases, modification of the procedure gives simple epoxidation. " Alkenes react with aldehydes and oxygen, with palladium-on-silica " or a ruthenium catalyst, " " ... 

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