Ruthenium nitro groups

The selective hydrogenation of an aryl nitro group has been accomplished even in the presence of an easily hydrogenated acetylene group. Cobalt polysulfide and ruthenium sulfide have been reported to be effective for the selective hydrogenation of the nitro group in m-nitrophenyl acetylenes giving the amino-acetylenes in 75-85% yields (Eqn. 19.2). Ruthenium catalysts were also effective for this reaction but since the order of reactivity over these catalysts was found to be ... 

Ru(CO)5 is less frequently used than Fe(CO)5 for organic synthesis or as a starting material as a zero-valent ruthenium complex because of its ease of decomposition to Ru4(CO),2 [99]. Dodecacarbonyltriruthenium is very useful for these purposes. It has been showm to be an active catalyst for the hydrogenation of olefins [100], carbonyla-tion of ethylene [101], hydroformylation of alkenes [102], water-gas shift reaction [103], and reduction of nitro groups [104], and recently, C—H bond activation [105] and coupling of diynes with CO [106]. 

Tris(triphenylphosphine)ruthenium(ll) chloride is a good catalyst for the homogeneous hydrogenation of aliphatic aldehydes to alcohols. Ketones and nitro-groups are not reduced under these conditions. ... 

Attack of methoxide (in DMSO to maximize its chemical potential) at 5-nitro-1,10-phenanthroline, free and co-ordinated to iron(n) and ruthenium(u), has been demonstrated by 220 MHz H n.m.r. spectroscopy. The Meisenheimer-com-pound from the free ligand is stable for days in a sealed tube its n.m.r. spectrum shows the methoxide to be at the 6-position, ortho- to the nitro-group (9). Attack... 

This reaction requires y-irradiation. However, the same complex (Ar = Ph) can also be obtained by reaction of PI1NO2 with Fc2(CO)9 [50]. It has also been observed that the formation of nitroso complexes from nitroarenes readily proceeds even with a ruthenium complex, provided a phenolic group is present in ortho to the nitro group (eq. 16) [53] ... 

The second strategy, implemented to increase the efficiency of Hoveyda-type catalyst, uses electronic effects to weaken the ruthenium-oxygen bond in 6. Thus, Grela reported the synthesis of catalyst 20 bearing a nitro group in para position to the isopropoxy ligand [32] (Scheme 12). 

Primary Amines.—Cobalt polysulphide and ruthenium(iv) sulphide catalysts have been found to be selective for the preferential hydrogenation of aromatic nitro-groups in the presence of acetylenes/ Formamidinesulphinic acid/ phenylselenol in the presence of DABCO/ and sodium borohydride in the presence of [Cu(acac)2r also effect the aromatic nitro-to-amine conversion. 

The ability of sol-gel entrapped compounds to catalyze reactions that do not take place by the non-entrapped materials is even more pronounced when an alumina sol-gel matrix is used. For example, while dihydrogen treated of triosmium- and triruthenium dodecacarbonyls [i.e., H40s4(C0)i2 andH4Ru4(CO)i2] are poor hydrogenation catalysts (see e.g., Ma, 1990) their immobilized versions in alumina sol-gel are highly active catalysts for the reduction ofalkenes and nitro groups at 60°C under 20-25 atm, H2 (Schemes 24-27 and 24-28). The alumina sol-gel entrapped ruthenium carbonyl complex even catalyzes... 

In place of active methylene compounds having a nitrile group, malonates, 13-ketoesters, 1,3-diketones, 1,1-disulfones, nitro compounds, Mel drum acid, and anthrone can also be used as the Michael donors for these ruthenium-catalyzed aldol and Michael reactions. The reaction proceeds well in acetonitrile under mild and neutral conditions (Eq. 9.59) [83]. 

Hydrogenation Catalysts. The key to catalytic hydrogenation is the catalyst, which promotes a reaction which otherwise would occur too slowly to be useful. Catalysts for the hydrogenation of nitro compounds and nitriles are generally based on one or more of the group VIII metals. The metals most commonly used are cobalt, nickel, palladium, platinum, rhodium, and ruthenium, but others, including copper (16), iron (17), and tellurium... 

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