Cluster ruthenium hydrogenation catalysts

Tetraruthenium dodecacarbonyl tetrahydride and some of its phosphine-substituted derivatives have been tested as homogeneous hydrogenation catalysts. The hydrogenation of cyclohexanone in the presence of H₄Ru₄(CO)₁₂ is first order with respect to the catalyst concentration, the substrate concentration and the partial pressure of hydrogen. The ruthenium cluster is recovered unchanged at the end of the reaction.     

Solid-phase synthesis of homogeneous ruthenium catalysts on silica for the continuous asymmetric transfer hydrogenation reaction

The solid-phase synthesis of new asymmetric transfer hydrogenation catalysts as well as the use of these silica supported systems in batch and flow reactors is reported. The ruthenium complex of NH-benzyl-(1R,2S)-(-)-norephedrine covalently tethered to silica showed a high activity and enantioselectivity in the reduction of acetophenone. In three consecutive batchwise catalytic runs, we obtained ee values of 88%. In a continuous flow reactor, a very constant catalytic activity was observed; no catalyst deactivation occurred over a period of one week. This has been ascribed to successful site isolation. Using optimized conditions in this flow reactor, the ee was as high as 90% at 95% conversion. The supported catalysts generally show the same trend in catalyst performance as in solution. The viability of our approach was further shown in one example, the ruthenium(II) complex of (1S,2R)-(+)-2-amino-1,2-diphenylethanol, for which an enantiomeric excess of 58% was observed, which is nearly three times higher than its homogeneous analogue.     

Catalytic hydrogenation of aromatic aldehydes and ketones over ruthenium catalysts

Catalytic hydrogenations of acetophenone, benzaldehyde, and cinnamaldehyde using a catalyst of 5% wt. Ru/activ. carbon in hexane and/or 2-propanol were studied. Basic kinetic parameters were evaluated. The influence of the reactants’ structure and the kind of solvent used on the course of the reaction were also discussed.     

Homogeneous hydrogenation of ketones to alcohols with ruthenium complex catalysts

A number of ruthenium triphenylphosphine complexes catalyse the reduction of ketones to their corresponding alcohols in the presence of water. The most convenient catalyst precursors are carbonyl containing complexes which do not promote decarbonylation of the substrate. The hydrogenation of acetone with hydridochlorocarbonyltris(triphenylphosphine)ruthenium is first order with respect to the substrate concentration, the catalyst concentration, the hydrogen pressure and the water concentration. Turnover numbers up to 15,000 have been achieved with this catalyst. Other ketones are also reduced by RuHCl(CO)(PPh₃)₃ and the rate of the reaction is dependent on the nature of the substrate.     

Deactivation of silica supported Pd catalysts during liquid-phase hydrogenation

Summary Large pore MCM-41 was found to provide a better stabilization of Pd particles than amorphous SiO₂ during liquid phase hydrogenation. Pd/large pore MCM-41 exhibited higher hydrogenation activities as well as lower amount of metal loss by Pd leaching.     

Liquid phase hydrogenation of some heterocyclic nitrogen compounds over ruthenium catalysts

Results are given for the hydrogenation of some heterocyclic nitrogen compounds (pyrrole, pyridine, indole, quinoline, and acridine) and certain derivatives of them in the liquid phase under pressure, in the presence of ruthenium catalysts. The results obtained indicate that these catalysts are very effective, making it possible to obtain high yields of the corresponding saturated compounds. In the cases of quinoline and acridine, depending on the temperature, double bonds in the polycyclic systems can be selectively hydrogenated.     

Transfer hydrogenation of cellulose to sugar alcohols over supported ruthenium catalysts

Ru/C catalysts are active for the conversion of cellulose using 2-propanol or H(2) of 0.8 MPa as sources of hydrogen, whereas the Ru/Al(2)O(3) catalyst is inactive in both reactions, indicating that the Ru/C catalysts are remarkably effective for the cellulose conversion.     

Activation of nickel–chromium hydrogenation catalysts with hydrogen

The kinetics of the reduction of nickel cations in nickel oxide and nickel–chromium catalysts whose oxide precursors have different structures has been investigated by thermal analysis. The reduction of nickel oxide with a hydrogen-containing gas takes place at 250–330°C. The apparent activation energy of this reaction is about 88 kJ/mol. The introduction of up to 30 at % chromium cations into the nickel oxide structure shifts the reduction temperature of nickel in the oxide phase to 300–450°C and increases the apparent activation energy of the reduction of nickel cations to ～108 kJ/mol. The introduction of 67 at % chromium into nickel oxide results in the formation of an oxide precursor with a spinel structure. The apparent activation energy of the reduction of nickel cations in this spinel is about 163 kJ/mol. The results of this study can be used in optimizing the composition of Ni-containing hydrogenation catalysts and their activation and operation conditions.     

硅纳米管负载的钌基催化剂费-托合成催化性能研究

以模板法合成的硅纳米管（SNT）为载体,用浆态浸渍法制备了钌基催化剂,采用氮气物理吸附、透射电子显微镜（TEM）、X射线粉末衍射（XRD）和氢气程序升温还原（H₂-TPR）等手段对其进行了表征。在固定床反应器上（503K,1.0MPa）考察了该催化剂的费-托合成反应活性及产物选择性,并与用商业二氧化硅为载体制备的催化剂上的反应结果进行了比较。结果表明,SNT和SiO₂负载的氧化钌在623K可被H₂完全还原;SNT负载的钌基催化剂上,钌氧化物颗粒较小、分散性好,还原后钌颗粒被较好地分散在硅纳米管上,且几乎所有的钌颗粒都分布在管内。与以SiO₂为载体的催化剂相比,以硅纳米管为载体的钌基催化剂具有较高的费-托合成活性。     

Studies of the kinetics and mechanism of glucose hydrogenation over ruthenium catalysts

Glucose hydrogenation has been studied in weakly alkaline water-ethanol media over 5% Ru/Al₂O₃. The solvent is shown to affect the activity and selectivity.

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- 5% Ru/Al₂O₃. .

     

Asymmetric hydrogenation of aromatic ketones with MeO-PEG-supported BIPHEP/DPEN ruthenium catalysts

A soluble polymer (MeO-PEG) supported biphenylbisphosphine (BIPHEP)-Ru/chiral diamine (1,2-diphenylethylenediamine) complex, in which the polymer is attached to the two phenyl rings of BIPHEP ligand, has been prepared, and shown to be highly active with good enantioselectivity for the catalyzed asymmetric hydrogenation of unfunctionalized aromatic ketones. The derived chiral ruthenium complex 5 proved to be stable in air allowing facile catalyst recycling. Especially for 4′-tert-butyl-acetophenone and 1-acetonaphthone, excellent ee values up to 96.5% and 95.9% have been obtained which are comparable to or even higher than the enantioselectivity achieved with 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl-Ru-DPEN catalyst under similar conditions.     

Transfer hydrogenation of aryl ketones with homogeneous ruthenium catalysts containing diazafluorene ligands

Novel cationic ruthenium(II) complexes bearing a 4,5‐diazafluorene unit and p‐cymene as ligands have been synthesised. The complexes were characterised based on elemental analysis and Fourier transform infrared and nuclear magnetic resonance spectroscopies. The synthesised Ru(II) complexes were employed as pre‐catalysts for the transfer hydrogenation of aromatic ketones using 2‐propanol as both hydrogen source and solvent in the presence of NaOH. All complexes showed high catalytic activity as catalysts in the reduction of substituted acetophenones to corresponding secondary alcohols. The products of catalysis were obtained with conversion rates of between 80 and 99%. Among the seven new complexes investigated, the most efficient catalyst showed turnover frequencies in the range 255–291 h^?1 corresponding to 85 to 97% conversion, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Mesoporous silica anchored Ru catalysts for highly enantioselective hydrogenation of beta-ketoesters

Recyclable and reusable mesoporous silica anchored Ru catalysts based on 4,4'-substituted BINAPs were synthesized and used for the hydrogenation of beta-alkyl beta-ketoesters with up to 98.6% e.e. and beta-aryl beta-ketoesters with up to 95.2% e.e.     

In situ formation of ruthenium catalysts for the homogeneous hydrogenation of carbon dioxide

A total of 44 different phosphines were tested, in combination with [RuCl(2)(C(6)H(6))](2) and three other Ru(II) precursors, for their ability to form active catalysts for the hydrogenation of CO(2) to formic acid. Half (22) of the ligands formed catalysts of significant activity, and only 6 resulted in very high rates of production of formic acid. These were PMe(3), PPhMe(2), dppm, dppe, and cis- and trans-Ph(2)PCH=CHPPh(2). The in situ catalysts prepared from [RuCl(2)(C(6)H(6))](2) and any of these 6 phosphine ligands were found to be at least as efficient as the isolated catalyst RuCl(O(2)CMe)(PMe(3))(4). There was no correlation between the basicity of monophosphines (PR(3)) and the activity of the catalysts formed from them. However, weakly basic diphosphines formed highly active catalysts only if their bite angles were small, while more strongly basic diphosphines had the opposite trend. In situ (31)P NMR spectroscopy showed that trans-Ru(H)(2)(dppm)(2), trans-RuCl(2)(dppm)(2), trans-RuHCl(dppm)(2), cis-Ru(H)(O(2)CH)(dppm)(2), and cis-Ru(O(2)CH)(2)(dppm)(2) are produced as the major metal-containing species in reactions of dppm with [RuCl(2)(C(6)H(6))](2) under catalytic conditions at 50 degrees C.     

Studies on ruthenium(II) Schiff base complexes as catalysts for transfer hydrogenation reactions

The reactions of [RuHCl(CO)(B)(EPh₃)₂] (B = EPh₃ or Py; E = P or As) and Schiff bases in 1:1 molar ratio led to the formation of [RuCl(CO)(EPh₃)(B)(L)] (E = P or As; B = PPh₃, AsPh₃ or Py; L = Schiff base ligand). The new complexes have been characterized by analytical and spectroscopic (IR, electronic and ¹H NMR) data. They have been assigned an octahedral structure. The new complexes were found to catalyse the transfer hydrogenation of ketones.     

Computational study of the factors controlling enantioselectivity in ruthenium(II) hydrogenation catalysts

The reduction of prochiral ketones catalyzed by Ru(diphosphine)(diamine) complexes has been studied at the DFT-PBE level of theory. Calculations have been conducted on real size systems [trans-Ru(H)2(S, S-dpen)(S-xylbinap) + acetophenone], [trans-Ru(H)2(S, S-dpen)(S-tolbinap) + acetophenone] and [trans-Ru(H)2(S, S-dpen)(S-xylbinap) + cyclohexyl methyl ketone] with the aim of identifying the factors controlling the enantioselectivity in Ru(diphosphine)(diamine) catalysts. The high enantiomeric excess (99%) in the hydrogenation of acetophenone catalyzed by trans-Ru(H)2(S, S-dpen)(S-xylbinap) has been explained in terms of the existence of a stable intermediate along the reaction pathway associated with the (R)-alcohol. The formation of this intermediate is hindered with the competitive pathways, which consequently increases the activation energy for the hydrogen transfer acetophenone/(S)-phenylethanol reaction. For the [trans-Ru(H)2(S, S-dpen)(S-tolbinap) + acetophenone] system, the lower enantioselectivity (i.e. 80%) is rationalized by the smaller differences in the activation energy between the competitive pathways which differentiate between the two diastereomeric approaches of the prochiral ketone. The DFT-PBE results suggest that this reaction is driven to the (R)-product only by the process of binding the acetophenone to the active site of the trans-Ru(H) 2(S, S-dpen)(S-tolbinap) catalyst. For the hydrogenation of cyclohexyl methyl ketone catalyzed by trans-Ru(H)2(S, S-dpen)(S-xylbinap), the low performance in the enantioselective hydrogenation of the dialkyl ketone (i.e. 37%) is again explained by the small differences in the activation and binding energies which are the factors which could effectively differentiate between the two alkyl groups.