Ruthenium Cluster Compounds

Ruthenium cluster compounds (143) and (144) have been identified that may play a role in the catalysis when Ru3(CO)12 was used as the precursor.540-543 The use of [(dppe)Ru(CO)3] as a catalyst including the intermediates (145) and (146) in the catalytic cycles, have been studied in detail by Gladfelter and co-workers.544-550... 

Gold-197 Mossbauer Data for the Gold Sites in Gold-Ruthenium Cluster Compounds, in Order of Isomer Shift... 

The formation of carbido-carbonyl cluster compounds with ruthenium and osmium appears to be common in pyrolysis reactions the basic reaction may be viewed as the transformation of the coordinated carbon monoxide to carbide and carbon dioxide. Small variations in... 

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... 

Metal carbonyl cluster compounds which contain three ruthenium or three osmium atoms in the cluster core are common.1 Potentially useful reagents for syntheses of these compounds are the triruthenium and triosmium dianions [M3(CO)h]2 (M = Ru, Os).2 Therefore, it is desirable to develop good synthetic routes to obtain [M3(CO)11]2- (M = Ru, Os) of high purity in high yields. A method that is particularly useful for generating [M3(CO)n]2 (M = Ru, Os) is the designed stoichiometric reduction of M3(CO)12 (M = Ru, Os) using an electron carrier such as potassium-benzophenone.3... 

Recent work by Ford et al. demonstrates that a variety of metal carbonyl clusters are active catalysts for the water-gas shift under the same reaction conditions used with the ruthenium cluster (104a). In particular, the mixed metal compound H2FeRu3(CO)13 forms a catalyst system much more active than would be expected from the activities of the iron or ruthenium systems alone. The source of the synergetic behavior of the iron/ruthenium mixtures is under investigation. The ruthenium and ruthenium/iron systems are also active when piperidine is used as the base, and in solutions made acidic with H2S04 as well. Whether there are strong mechanistic similarities between the acidic and basic systems remains to be determined. 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

The possibility of coordination of a two-electron ligand, in addition to arene, to the ruthenium or osmium atom provides a route to mixed metal or cluster compounds. Cocondensation of arene with ruthenium or osmium vapors has recently allowed access to new types of arene metal complexes and clusters. In addition, arene ruthenium and osmium appear to be useful and specific catalyst precursors, apart from classic hydrogenation, for carbon-hydrogen bond activation and activation of alkynes such compounds may become valuable reagents for organic syntheses. 

Pyrolysis reactions of mononuclear carbonyls and low-nuclearity cluster compounds have been used extensively in the syntheses of HNCC of osmium (54, 72,80,95,108), ruthenium (18,20,29), and, more recently, rhenium (2-4). The reactions have been carried out either in inert solvents or, to facilitate the ejection of CO or other volatile ligands, in the solid state under vacuum. Condensation processes under pyrolytic conditions are rarely specific and, as such, lead to the formation of a wide range of products. In order to obtain optimum yields of a particular HNCC, the reaction conditions must be carefully screened. Solution reactions offer advantages such as the ability to monitor the progress of the reaction using IR spectroscopy. As they often give... 

Examples of the first type of these reactions are found in several systems but the reaction mechanisms may follow different pathways. One route is substitution of one of the carbonyl ligands as has been observed in some osmium and ruthenium complexes (458, 459). The other mechanism involves metal-metal bond fission (414, 428), and in some cases this means the formation of cluster compounds with a smaller number of metal atoms [Eq. (20)] (460). 

There are syntheses where the new metallic species enhances a different type of reactivity. This has been observed in the reactions between alkyne-substituted ruthenium clusters and compounds of mercury (145, 146). In most of the characterized products a mercury atom or an HgX2 (X = halogen) fragment serves as a bridge between two ruthenium cluster frameworks which retain the coordinated alkyne. 

Among the several species shown in Fig. 12, two special classes of compounds were systematically studied (31, 38, 39), consisting of tetrasubstituted pyridylpor-phyrins coordinated with four ruthenium-polypyridines (here denoted tetraruthe-nated pyridylporphyrin, TRPyP) or triangular ruthenium clusters (here denoted tetracluster pyridylporphyrin, TCPyP) (Fig. 13). 

Although ruthenium is significantly less expensive than rhodium and although its use has been recommended since 1960 (7) for the oxo synthesis, complexes of this metal have not been developed as catalysts. However, many papers and patents have referred to the results obtained employing various ruthenium complexes. The purpose of this article is to analyze the work done involving ruthenium compounds, restricting the scope only to the hydroformylation reaction and not to the carbonylation reaction, which would demand to too lengthy an article. In this review we examine successively mononuclear ruthenium complexes, ruthenium clusters as precursors, photochemical activation, and supported catalysis. 

This section surveys the use of various di-, tri-, and polynuclear ruthenium complexes as precursors for the homogeneous hydroformylation of alkenes. Several arbitrary assumptions have been made so as to include dinuclear starting complexes which are strictly not cluster compounds. Moreover, no distinction is made between neutral and anionic precursors. Also, in several cases, particularly in the patents, information is lacking concerning the intermediate species involved in the catalytic cycles. Interestingly, half of the described systems come from patents, and there are few fundamental studies which clearly establish the implication of cluster species during the catalysis. 

The reactions of nitric oxide with metal cluster compounds themselves are complicated by the possibility of metal—metal bond cleavage. In the next example, the tri-iron compound shows very different reactivity from its ruthenium and osmium analogs (26-28) ... 

Heterocyclic compounds possessing the structural pattern of orthoamides were obtained by spirocycli-zation of isocyanates in the presence of triethylsilane catalyzed by a ruthenium cluster (equation... 

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