Ruthenium carbonyl, Ru3

Ford and co-workers have also recently developed a homogeneous catalyst system for the water-gas shift reaction (95). Their system consists of ruthenium carbonyl, Ru3(CO)12, in an ethoxyethanol solvent containing KOH and H20 under a CD atmosphere. Experiments have been conducted from 100-120°C. The identity of the H2 and CD2 products has been confirmed, and catalysis by both metal complex and base has been verified since the total amount of H2 and COz produced exceeds the initial amounts of both ruthenium carbonyl and KOH. The authors point out that catalysis by base in this system depends on the instability of KHC03 in ethoxyethanol solution under the reaction conditions (95). Normally the hydroxide is consumed stoichiometrically to produce carbonate, and this represents a major reason why a water-gas shift catalyst system has not been developed previously under basic conditions. As has been noted above, coordinated carbonyl does not have to be greatly activated in order for it to undergo attack by the strongly nucleophilic hydroxide ion. Because of the instability of KHC03... 

The only readily available ruthenium carbonyl, Ru3(CO)i2, reacts in a complex manner with many polyolefins to give, in addition to mononuclear derivatives, complexes retaining the Rus cluster and products resulting from hydrogen abstraction. ... 

Ruthenium carbonyl, Ru3(CO)12, has been reported to catalyze the cyclohydrocarbonylation of acetylene to give hydroquinone ... 

Apart from arenes, most carbon-carbon coupling reactions involve olefins. Ruthenium carbonyl, Ru3(CO)12, catalyzes the addition of aldehydes to olefins according to... 

Ruthenium carbonyl, Ru3(CO)i2, has been found to be active for the catalytic dimerization of methyl acrylate to give predominantly the transisomer of 91... 

The interaction of ruthenium carbonyl, Ru3(C0)j2 with rare earth oxides of high surface area, >50rrrg"l, has been studied. [Ru3(u H)(C0)jq(ii-0M=)] is formed on holmia, but on lanthana only [Ru(C0)o]n species are observed. Reduction of the carbonyl ligands takes place at <573K to give catalysts for the hydrogenation of carbon monoxide with activity and selectivity dependent on the particular rare earth oxide and pretreatment. Over ceria, the product is up to 55 wt% C2-5 olefins. A similar selectivity is obtained over lanthana only after redispersion through a reduction-oxidation-reduction cycle. 

Ruthenium carbonyl, Ru3(C0)i2 rather than RuC13 was selected as the metal precursor, with a view to maximising the dispersion and minimising surface contamination by anions. Oxidation-reduction cycles have also been reported to increase dispersion of ruthenium and selectivity to higher hydrocarbons and, in particular, to olefins (4,5). Some preliminary results of our studies are reported here. 

The reaction of tetramethylthiourea, (Me2N)2CS, with ruthenium carbonyl, Ru3(CO)j 2> been studied under various conditions ... 

The dominant role of copper catalysts has been challenged by the introduction of powerful group VIII metal catalysts. From a systematic screening, palladium(II) and rhodium(II) derivatives, especially the respective carboxylates62)63)64-, have emerged as catalysts of choice. In addition, rhodium and ruthenium carbonyl clusters, Rh COJjg 65> and Ru3(CO)12 e6), seem to work well. Tables 3 and 4 present a comparison of the efficiency of different catalysts in cyclopropanation reactions with ethyl diazoacetate under standardized conditions. 

This system shows an induction period of about six hours before constant activity is attained during which the Ru3(C0)12 undergoes complete conversion to another ruthenium carbonyl complex. In situ nmr studies suggest this species to be the HRu2(C0)e ion. Kinetic studies show complex rate profiles however, a key observation is that the catalysis rate is first order in Pco at low pressures (Pcohigher pressures. A catalysis scheme consistent with these observations is proposed. 

The reactions with ruthenium carbonyl catalysts were carried out in pressurized stainless steel reactors glass liners had little effect on the activity. When trimethylamine is used as base, Ru3(CO) 2> H Ru4(CO) 2 an< H2Ru4(CO)i3 lead to nearly identical activities if the rate is normalized to the solution concentration of ruthenium. These results suggest that the same active species is formed under operating conditions from each of these catalyst precursors. The ambient pressure infrared spectrum of a typical catalyst solution (prepared from Ru3(CO)i2> trimethylamine, water, and tetrahydrofuran and sampled from the reactor) is relatively simple (vq q 2080(w), 2020(s), 1997(s), 1965(sh) and 1958(m) cm ). However, the spectrum depends on the concentration of ruthenium in solution. The use of Na2C(>3 as base leads to comparable spectra. 

Effect of Concentration and CO Pressures on the Ruthenium Carbonyl-Trimethylamine WGSR System. As shown in Figure 1, the RU3(CO) 2/NMe3 WGSR system demonstrates a nearly first-order rate dependence on CO pressure at 0.5 mM Ru3(CO) 2 concentration. (Throughout this discussion, the total ruthenium carbonyl concentration is expressed as moles Ru3(00) 2 added per liter of solution this should not be construed to be the actual solution concentration of the trimer under operating conditions.) Here the initial rates of H2 production are 14.6 mmol /hr at 415 psi CO and 46.0 mmol /hr at 1200 psi. Thus, within experimental uncertainty, a threefold increase in CO pressure leads to a threefold increase in rate. 

Table 2 Effect of the type of base on the ruthenium carbonyl catalyzed water gas shift reaction. Conditions 0.05 mmol Ru3(CO)12, 92 mmol 1-butene, base and water diluted to 100 ml with diglyme, 750 psi ( 52 atm) CO, 100 °C, 10 hours, 0.31 L reactor58 ... 

However, while ruthenium carbonyl was found to decompose the formate ion in basic media, the rate was slower (<0.1 mmol trimethyl ammonium formate to H2 and C02 per hour) than the rate of the water-gas shift reaction (>0.4 mmol H2/hr) at 5 atm CO and 100 °C. Increasing CO pressure decreased the formate decomposition rate. However, it was observed that increasing the CO pressure from 5 atm CO to 50 atm increased the H2 production rate to 10 mmol/hr. They proposed, in a similar manner to Pettit et al.,34 a mechanism that involved nucleophilic attack by amine (instead of hydroxide). Activation of the metal carbonyl (e.g., Ru3(CO) 2 cluster to Ru(CO)5) was suggested to be favored by dilution, increases in CO pressure, or, in the case of Group VIb metal carbonyl complexes, photolytic promotion. The mechanism is shown below in Scheme 9 ... 

Ruthenium carbonyl-derived catalytic systems have also been studied in hydrodesulfuration [118, 119], Highly active catalysts for the hydrodesulfuration of diben-zothiophene have been obtained by supporting on alumina MHRu3(CO)n (M = group 1 metal), which was the product of the reaction between Ru3(CO)i2 and MOH. The activity increased from Li to Cs [119]. 

Finally, the surface-mediated synthesis of ruthenium carbonyl complexes has also been used to prepare supported ruthenium particles. Using silica as a reaction medium and conventional salts, apart from Ru3(CO)i2, mononuclear Ru(CO)j, and high nuclearity carbonyl-derived species can be obtained by CO reductive carbonylation [127, 128]. This opens new routes to preparing tailored supported ruthenium particles. 

High-pressure infrared studies of ruthenium carbonyl solutions under H2/CO at temperatures employed for CO reduction have also been reported. In //-teiradecane solution at 180 C under 1 1 H2/CO, mainly Ru(CO)5 is detected (60). In acetic acid solvent at 200 C, only Ru(CO)5 is detected under 400 atm of 1 1 H2/CO at H2/CO pressures of 200 atm, Ru3(CO)l2 is also observed (166). Reaction solutions have also been studied by sampling under reaction conditions, rapidly cooling the samples to low temperatures, and analyzing them by infrared spectroscopy after reaction at 265 atm of 1 1 H2/CO at 180 C, only Ru(CO)s could be detected (164). At higher temperatures and lower pressures (100 atm of 1 1 H2/CO and 250"C), evidence was seen for the clusters Ru3(CO)l2 and H4Ru4(CO)l2 as well as Ru(CO)s (163). 

Submitted by MICHAEL 1. BRUCE and MICHAEL L. WILLIAMS Checked by GUY LAVIGNE and TH RESE ARLIGUIEt This tetranuclear ruthenium carbonyl hydride was described on several occasions,5 but early preparations were usually contaminated with Ru3(CO)12, giving rise to suggestions of the existence of two isomeric forms. The situation was clarified by the work of Kaesz and coworkers,6 who discovered the direct route from Ru3(CO)12 and hydrogen, which is described below. The compound is often obtained from reactions between Ru3(CO)12 and substrates containing hydrogen (hydrocarbons, ethers, alcohols, water, etc.) and by acidification of anionic ruthenium cluster carbonyls.7... 

Numerous investigations have been undertaken on the reactions of ruthenium carbonyls with olefins and acetylenes. Two complex types [55] and [56] result from the reaction of Ru3(CO)j2 with ethylene and other Simple olefins (127). The complexes [56], which belong to the products of reaction (1) (Chapter 2.5.) are also formed from Ru3(CO)i2 and diphenyl acetylene (183). [55] and [56] show interesting fluxional properties, and four different types of ligand scrambling are possible (163). 

The ruthenium carbonyl complexes [Ru(CO)2(OCOCH3)] n, Ru3(CO)12, and a new one, tentatively formulated [HRu-(CO)s ] n, homogeneously catalyze the carbonylation of cyclic secondary amines under mild conditions (1 atm, 75°C) to give exclusively the N-formyl products. The acetate polymer dissolves in amines to give [Ru(CO)2(OCOCH3)(amine)]2 dimers. Kinetic studies on piperidine carbonylation catalyzed by the acetate polymer (in neat amine) and the iiydride polymer (in toluene-amine solutions) indicate that a monomeric tricarbonyl species is involved in the mechanism in each case. 

Other Ruthenium Catalysts. Ru3(CO)i2 readily dissolved in piperidine to give a solution effective for catalytic carbonylation of the amine. The uptake plots resemble those shown in Figure 1 (curves B-E), and the maximum rate given in Table I refers to the initial rate. Attempts to characterize the ruthenium complexes formed from reaction of the dodecacarbonyl with amines have been unsuccessful. 

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