Ruthenium trichloride

The sequence has been applied to the synthesis of 1,4-cyclohexanedione from hydroquinone 10), using W-7 Raney nickel as prepared by Billica and Adkins 6), except that the catalyst was stored under water. The use of water as solvent permitted, after hltration of the catalyst, direct oxidation of the reaction mixture with ruthenium trichloride and sodium hypochlorite via ruthenium tetroxide 78). Hydroquinone can be reduced to the diol over /o Rh-on-C at ambient conditions quantitatively (20). 

It would be more convenient if 12 or a similar catalyst could be made in situ from precursors which are more air-tolerant than 6 and require fewer steps to make. (Phosphine 11 is air-sensitive but no more so than PPh3, which can be weighed and transferred in open air.) Complex 1 seemed a suitable candidate, for it is air-stable and can be made in one step from ruthenium trichloride, CpH, and PPh3,(21) and ligand substitutions are facile, particularly inprotic solvents. 

Scheme 150).225 227 The pyran products predominate when the ratio of triphenylphosphine to palladium catalyst exceeds two whereas the linear oligomers are the major products when this ratio is close to unity. The suggested227 mechanism (Scheme 151) includes a step of insertion of C=0 into a C—Pd palladium-catalyzed reactions leading to the formation of pyranones (see Scheme 152)228 and piperidones (see Scheme 139 in Section V,A,2).211 It is useful to note that the 2,5-divinyltetrahydropyran derivative can be transformed catalytically by ruthenium trichloride into synthetically useful 3,4-dihydro-2//-pyran derivatives (Scheme 153).229... 

Mild allylic oxidation of the A-2-crotyl-substituted thiadiazolidinone 1,1-dioxide 140 by sodium metaperiodate/ ruthenium trichloride hydrate (RuC13) gave the aldehyde 141. Excess oxidizing agent afforded the carboxylic acid 142 (Equation 26) <1999EJ02275>. 

The dichlororuthenium arene dimers are conveniently prepared by refluxing ethanolic ruthenium trichloride in the appropriate cyclohexadiene [19]. The di-chloro(pentamethylcyclopentadienyl) rhodium dimer is prepared by refluxing Dewar benzene and rhodium trichloride, whilst the dichloro(pentamethylcyclo-pentadienyl)iridium dimer is prepared by reaction of the cyclopentadiene with iridium trichloride [20]. Alternatively, the complexes can be purchased from most precious-metal suppliers. It should be noted that these ruthenium, rhodium and iridium arenes are all fine, dusty, solids and are potential respiratory sensitizers. Hence, the materials should be handled with great care, especially when weighing or charging operations are being carried out. Appropriate protective clothing and air extraction facilities should be used at all times. 

Methylbenzenes are oxidized to the corresponding benzoic acids in very high yield under phase-transfer catalytic conditions by sodium hypochlorite in the presence of ruthenium trichloride, which is initially oxidized to ruthenium tetroxide [5]. Absence of either the ruthenium or the quaternary ammonium salt totally inhibits the reaction. 

In the presence of ruthenium trichloride, alkaline sodium hypochlorite is able to oxidize methylbenzenes to benzoic acids under phase-transfer conditions at room temperature. In a recent development, selective oxidation of xylenes to toluic acids has... 

S. Wolf, S. K. Hasan, J. R. Campbel, Ruthenium Trichloride-Catalysed Hypochlorite Oxidation of Organic Compounds, Chem. Commun. 21 (1970) 1420—1421. 

Exposure of 144 to catalytic quantities of ruthenium tetroxide, generated in situ from ruthenium trichloride and sodium periodate, produces the symmetrical lactones 145 <2000JA9558>. It is proposed that the products form as a result of the ruthenium-catalyzed oxidative cleavage of the a-diketones to produce intermediate glycols (Equation 49). 

A solution of 18 g (68 mmol) of commercial ruthenium trichloride hydrate (Johnson Matthey, 40 3% ruthenium) in a mixture of isoprene (680 mL) and 2-methoxyethanol (280 mL) is heated at reflux for 10 days under inert gas (nitrogen or argon). The purple crystalline product is collected in a medium-porosity sintered-glass funnel, washed with diethyl ether, and dried in vacuo yield 19.9 g (95%). 

Under the argon atmosphere, a solution of hydrated ruthenium trichloride (approximately RuCl3 3H20, containing 38-39% Ru) (1.00 g, approximately 3.83 mmol) in 50 mL of ethanol was treated with 5 mL of y-terpinene and heated under reflux in a 100-mL, round-bottomed flask for 4h. The hot solution was filtered as quickly as possible to remove the undissolved dark residue. The filtrate was concentrated to 25 mL under reduced pressure and cooled to room temperature and the red-brown microcrystalline product that resulted was collected by filtration. After drying in vacuo (approximately 1 mmHg) for 4 h, 0.70 g (59.9 %) of ruthenium complex was obtained. 

Ruthenocene has been prepared in 20% yields by reaction of cyclopentadienylmagnesium bromide with ruthenium(III) acetyl-acetonate.8 More recently,4 the compound has been made in 43-52% yield by treatment of sodium cyclopentadienide with ruthenium trichloride in tetrahydrofuran or 1,2-dimethoxyethane. 

Dodecacarbonyltriruthenium can be prepared by several methods. Johnson and Lewis1 have reported a procedure in which ruthenium trichloride hydrate is converted to tris(2,4-pentanedionato)ruthenium(III), which is turn is reacted with hydrogen and carbon monoxide. Reaction pressure and temperature are high (160 atm and 165 °C) and the yield is in the range from 50 to 55%. 

Mantovani and Cenini3 have also reported a two-step ambient pressure synthesis of dodecacarbonyltriruthenium starting with ruthenium trichloride hydrate resulting in a 50 to 60% yield but the product requires recrystallization. 

In some instances, particularly when the ruthenium trichloride sample contains more than the usual amount of water (this may occur, e.g., with old samples or on long exposure to moist air), the isolated product may be a mixture of Ru3(CO)12 and Ru4(/ -H)4(CO)12 (as indicated by the IR v(CO) spectrum). In such cases, depending upon the final product required (a) the product may be used directly as in the synthesis of Ru4( -H)4(CO)12 described below, when conversion to the cluster carbonyl hydride is completed by reaction with H2 or (b) treatment of the product with CO for 1 h while suspended in refluxing octane, using the apparatus depicted in Fig. 1, results in conversion of any Ru4(/i-H)4(CO)12 to Ru3(CO)12. 

The heptane solvent should be dried over sodium wire and a few milliliters of heptane should be added to the autoclave outside the liner tube to improve thermal contact between the autoclave and the tube. Triruthenium dodecacar-bonyl is available commercially (Alpha and Strem) or may be made from hydrated ruthenium trichloride by well-known procedures.6... 

Tetrahydrofuran (THF) and diethyl ether are freshly distilled from sodium benzophenone ketyl under nitrogen. Hexane is freshly distilled from sodium metal under nitrogen. Triruthenium dodecacarbonyl is available commercially or it can be synthesized from ruthenium trichloride trihydrate (Alfa) using the procedure of Mantovani and Cenini,3a or alternately, by the procedure given in this volume.3b The [/r-nitrido-bis(triphenylphosphorus)(l+)] chloride can be purchased from Strem or synthesized according to the literature procedure4... 

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