Catalytic hydrogenation of nitrobenzene on solid sulfides and soluble rhenium thiocomplexes

Studies of the reduction of nitrobenzene in the catalytic hydrogenation on soluble rhenium thiocomplexes and solid ReS₂ and Re₂S₇ indicate that on homogeneous and heterogeneous rhenium sulfides it follows the same mechanism. Thiocomplexes are considered as possible analogs of the active sites in ReS₂ and Re₂S₇ sulfide catalysts.

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ReS₂ Re₂S₇. , . ReS₂ Re₂S₇.

     

Nucleophilic displacement of aromatic nitro groups

The relative nucleofugicity of the nitro group in many aromatic nucleophilic substitution reactions rivals, and in some cases surpasses, that of the fluorine atom. The use of the nitro function as a leaving group in such reactions facilitates the synthesis of novel substituted benzene derivatives and simplifies the synthesis of a wide variety of heterocycles.     

Mechanistic investigation on hydrogenation and hydrosilylation of ethylene catalyzed by rhenium nitrosyl complex

The mechanistic study for hydrogenation and hydrosilylation of ethylene catalyzed by a rhenium nitrosyl complex is carried out with the aid of density functional theory computations. The hydrogenation of ethylene is found to be available kinetically in which the oxidative addition of H₂ plays a role in decreasing the reaction barrier. For the case of hydrosilylation of ethylene, it is found the oxidative addition of HSiMe₃ cannot occur due to steric reasons, instead, a σ-bond metathesis process for reductive elimination of C₂H₅SiMe₃ is proposed. The major reason for the inaccessibility for the hydrosilylation is resulted from the fact that the oxidative addition of HSiMe₃ cannot give a more stable intermediate.     

Catalytic hydrogenation of aromatic nitro compounds by non-noble metal complexes of chitosan

Silica-supported mono-metal (such as Ni, Cu) complexes and mixed metal (such as Cu/Zn, Cu/Cr) complexes of chitosan have been prepared. It is found that these non-noble metal complexes could be used as efficient catalysts for the hydrogenation of aromatic nitro compounds. The effects of type of metal, reaction temperature and pressure, solvent, nitrogen/metal molar ratio in the complex catalysts on the yields from nitrobenzene to aniline have been examined. It was also found that catalysts are active for the catalytic hydrogenation of other aromatic nitro compounds such as 2-nitroanisole, 2-nitroaniline, 2-nitrotoluene and 1-chloro-4-nitrobenzene.     

Oxidation of polycyclic aromatic hydrocarbons catalyzed by soybean peroxidase

Soybean peroxidase (SBP) catalyzes the oxidation of a variety of polycyclic aromatic hydrocarbons (PAHs) in the presence of water-miscible organic cosolvents, including acetonitrile, tetrahydrofuran, and dimethylformamide (DMF). Oxidation was optimal at pH 2.0–2.5, with substantially lower reactivity at pH 1.5 as well as at pH > 3.0. Despite the low pH activity optimum, SBP had an observed half-life of 120 h at pH 2.5. Conversions of greater than 90% were observed with anthracene and 9-methylanthracene in the presence of 50% (v/v) DMF. Anthracene oxidation yielded exclusively anthraquinone, thereby demonstrating that SBP catalyzes a formal six-electron oxidation of the unactivated aromatic substrate to the quinone. A mechanism is proposed to account for this reaction that includes the initial one-electron oxidation of the PAH followed by addition of water to the oxidized PAH. 9-Methylanthracene was more reactive than anthracene, and its enzymatic oxidation yielded two products: anthraquinone and 9-methanol-9,10-dihydroanthracene. The former product indicates that loss of the methyl group occurs during enzymatic oxidation. These results suggest that SBP could be useful in the conversion of PAHs into more environmentally benign materials.     

Wilkinson's catalyst catalyzed selective hydrogenation of olefin in the presence of an aromatic nitro function: a remarkable solvent effect

Optimal conditions for chlorotris(triphenylphosphine)rhodium(I) (Wilkinson's catalyst) catalyzed selective saturation of a double bond in the presence of a nitro function are developed. Aryl iodide and benzyl ether are also tolerated under these hydrogenation conditions.     

Properties of photoimmobilized phosphorus-containing rhenium complexes in hydrogenation of the olefin bond and the nitro group

We show it is possible to activate cis-ReOBr₃(PPh₃)₂ (inactive under homogeneous catalysis conditions) by photoimmobilization on different supports and we investigate the activity of the systems obtained in liquid-phase hydrogenation 1-hexene and m-nitrobenzoic acid. We propose various mechanisms for grafting the complex in the dark and under the action of UV irradiation. The samples photoimmobilized on agnate are not effective as catalysts, which is connected with the positive effect of the support itself on formation of active centers.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 6, pp. 533–538, November–December, 1993.     

Catalytic transfer hydrogenation of aromatic nitro compounds in the presence of nickel thiolato-complexes

Summary Transfer hydrogenation of aromatic nitro compounds by hydrazine to the corresponding anilines is catalyzed by (Bu₄N)[Ni(tdt)₂] (tdt=toluene-3,4-dithiolate) and analogous Ni^III complexes in refluxing THF; hydroxylamine derivatives are formed as intermediates.     

Pd-catalyzed silicon hydride reductions of aromatic and aliphatic nitro groups

[reaction: see text] Room-temperature reduction of aromatic nitro groups to amines can be accomplished in high yield, with wide functional group tolerance and short reaction times (30 min) using a combination of palladium(II) acetate, aqueous potassium fluoride, and polymethylhydrosiloxane (PMHS). Replacing PMHS/KF with triethylsilane allows aliphatic nitro groups to be reduced to their hydroxylamines.     

Oxygenation of aromatic hydrocarbons with hydrogen peroxide catalyzed by rhodium carbonyl complexes

Hexanuclear rhodium carbonyl cluster, Rh₆(CO)₁₆, catalyzes benzene hydroxylation with hydrogen peroxide in acetonitrile solution. Phenol and (at lower concentration) quinone are formed with the maximum attained total yield and turnover number 17% and 683, respectively. Certain other rhodium carbonyl complexes, containing cyclopentadienyl ligands, Rh₂Cp₂(CO)₃ and Rh₃(CpMe)₃(CO)₃, are less efficient catalysts. Cyclopentadienyl derivatives of rhodium which do not contain the carbonyl ligands, Rh(CpMe₅)(CH₂?CH₂)₂, RhCp(cyclooctatetraene) and Rh₂Cp₂(cyclooctatetraene) turned out to be absolutely inactive in the benzene hydroxylation. Styrene is transformed into benzaldehyde and (at lower concentration) acetophenone and 1‐phenylethanol. Copyright © 2008 John Wiley & Sons, Ltd.     

Selective catalytic hydrogenation of nitro groups in the presence of activated heteroaryl halides

Chemoselective reduction of nitro groups in the presence of activated heteroaryl halides was achieved via catalytic hydrogenation with a commercially available sulfided platinum catalyst. The optimized conditions employ low temperature, pressure, and catalyst loading (<0.1 mol % Pt) to afford heteroaromatic amines with minimal hydrodehalogenation byproducts.     

Asymmetric hydrogenation of aromatic ketones catalyzed by achiral monophosphine TPPTS-stabilized Ru in ionic liquids

Achiral monophosphine TPPTS [TPPTS: P(m-C₆H₄SO₃Na)₃]-stabilized Ru was synthesized by reduction of RuCl₃·3H₂O with hydrogen in ethanol using TPPTS as the stabilizer. The catalytic asymmetric hydrogenation of aromatic ketones using TPPTS-stabilized Ru modified by a chiral diamine (1R,2R)-DPENDS [disodium salt of sulfonated (1R,2R)-1,2-diphenyl-1,2-ethylene-diamine] was investigated in hydrophilic ionic liquid [RMIM]Ts (1-alkyl-3-methylimidazolium p-methylphenylsulfonates, R = ethyl, butyl, octyl, dodecyl, hexadecyl). Hundred percent conversion and 85.1% ee were obtained for acetophenone under optimized conditions. The resulting products can be easily separated from the catalyst immobilized in ionic liquid by simple extraction with n-hexane, and the catalyst can be reused several times without a significant loss of ee value or conversion. In particular, the addition of water can improve the catalyst performance.     

Formation of aromatic hydrocarbons in CO hydrogenation over silica gel-supported palladium

It has been established that several aromatic hydrocarbons are formed in CO hydrogenation over silica gel-supported palladium catalysts. A mechanism for the formation of reaction products is suggested.

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活性炭负载氢氧化氧铋催化水合肼还原芳香族硝基化合物

采用浸渍法制备了BiO(OH)/C催化剂。催化剂的XRD谱表明,当催化剂中BiO(OH)的质量分数小于10%时,BiO(OH)在活性炭中高度分散。反应温度为75 ℃时,催化剂重复使用7次仍保持较高活性。在5 mL乙醇中以0.05 g 10%（质量分数）BiO(OH)/C,1 mmol芳香族硝基化合物和2 mmol水合肼于75 ℃反应一定的时间,所得芳胺的收率为88%～99%。     

Graphite catalyzed reduction of aromatic and aliphatic nitro compounds with hydrazine hydrate

Aromatic and aliphatic nitro compounds were readily reduced to amino compounds in excellant yields with graphite and hydrazine hydrate.     

Influence of substituents on the through-space shielding of aromatic rings

A series of naphthalene derivatives, bearing a methyl group and a substituted phenyl ring in a 1,8-relationship, have been synthesized. The chemical shifts of the protons of the methyl group, which are pointed toward the shielding zone of the phenyl ring, were monitored as the phenyl substituents were varied. This work indicates that the shielding effect of the phenyl ring is not so severely altered by the substituents as to significantly influence the chemical shift of the methyl group. Nonetheless, within the small changes observed experimentally, there appears to be a tendency for electron-withdrawing X to shift the methyl signal downfield, whereas electron-donating X-groups cause a more upfield shift. Polarization and field effects are discussed as possible causes for this phenomenon. Chemical shifts computed for selected members of the series, using the recently published procedures of Rablen and Bally, are in agreement with the experimentally observed trends.