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Hydrogenation Reactions (hydrogenation + reaction)
Kinds of Hydrogenation Reactions Selected AbstractsAir-Stable and Highly Active Dendritic Phosphine Oxide- Stabilized Palladium Nanoparticles: Preparation, Characterization and Applications in the Carbon-Carbon Bond Formation and Hydrogenation ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2008Lei Wu Abstract Dendrimer-stabilized palladium nanoparticles were formed in the reduction of palldium bis(acetylacetonate) [Pd(acac)2] in the presence of phosphine dendrimer ligands using hydrogen in tetrahydrofuran. The resulting Pd nanoparticles were characterized by TEM, 31P,NMR and 31P MAS NMR. The results indicated that the dendritic phosphine ligands were oxidized to phosphine oxides. These dendrimer-stabilized Pd nanoparticles were demonstrated to be efficient catalysts for Suzuki and Stille coupling reactions and hydrogenations. The dendritic wedges served as a stabilizer for keeping the nanoparticles from aggregating, and as a vehicle for facilitating the separation and/or the recycling of the Pd catalyst. In the case of the Suzuki coupling reaction, these Pd nanoparticles exhibited high catalytic efficiency (TON up to 65,000) and air stability as compared with the commonly used homogeneous catalyst tetrakis(triphenylphosphine)palladium [Pd(PPh3)4]. In addition, the results obtained from the bulky dendritic substrate suggest that the Pd nanoparticles might act as reservoir of catalytically active species, and that the reaction is actually catalyzed by the soluble Pd(0) and/or Pd(II) species leached from the nanoparticle surface. [source] PhthalaPhos: Chiral Supramolecular Ligands for Enantioselective Rhodium-Catalyzed Hydrogenation Reactions,ANGEWANDTE CHEMIE, Issue 37 2010Luca Pignataro Dr. Wasserstoffbrücken verknüpfen chirale einzähnige Phosphitliganden mit H-Brückendonor- und -akzeptorgruppen zu supramolekularen zweizähnigen Liganden, deren Rhodiumkomplexe (siehe Bild) bei der katalytischen Hydrierung von Standard- und industrierelevanten Substraten hohe Enantiomerenüberschüsse ergeben. cod=1,5-Cyclooctadien. [source] Homogeneous Stabilization of Pt Nanoparticles in Dendritic Core,Multishell Architectures: Application in Catalytic Hydrogenation Reactions and RecyclingCHEMCATCHEM, Issue 7 2010Juliane Keilitz Abstract Core,multishell architectures are a new approach to homogeneously stabilize metal nanoparticles for harsh conditions. Herein, we present the synthesis and stabilization of Pt nanoparticles in dendritic core,multishell polymers and their application in hydrogenation reactions. The successful recycling of the catalyst was demonstrated for the hydrogenation of methyl crotonate 1 and was either achieved by ultrafiltration or in a two-phase system for at least 14,cycles. Thereby, the total turnover number (TON) was increased to 22,000. In the recycling experiments, low metal leaching into the product (as low as 0.3,ppm) was detected. Additionally, the selective hydrogenation of isophorone 3 was investigated and selectivities of 99:1 for CC versus CO hydrogenation were achieved. [source] Estimation of Kinetic Parameters for Hydrogenation Reactions Using a Genetic AlgorithmCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2009A. Kadiva Abstract The kinetics of acetylene hydrogenation in a fixed-bed reactor of a commercial Pd/Al2O3 catalyst has been studied. The hydrogenation reactor considered in this work is an essential part of a vinyl chloride monomer (VCM) plant. Three well-known kinetic models were used to simulate the hydrogenation reactor under industrial operating conditions. Since none of the models provide appropriate prediction, the industrial data and calculated values were compared and optimum kinetic parameters were evaluated utilizing a genetic algorithm (GA) technique. The best kinetic parameters for the three models were determined under specified industrial operating conditions. The hydrogenation reactor was simulated using the estimated optimum kinetic parameters of the three models. Simulation results from the three models were compared to industrial data and the best kinetic model was found. This kinetic model with the evaluated optimum kinetic parameters can well predict the behavior of the industrial hydrogenation reactor to improve the performance of the process. [source] ChemInform Abstract: Sequence of Intramolecular Carbonylation and Asymmetric Hydrogenation Reactions: Highly Regio- and Enantioselective Synthesis of Medium Ring Tricyclic Lactams.CHEMINFORM, Issue 40 2008Shui-Ming Lu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Mixed Donor Aminophosphine Oxide Ligands in Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation Reactions.CHEMINFORM, Issue 43 2004Mohammed S. Rahman Abstract For Abstract see ChemInform Abstract in Full Text. [source] A Novel Chiral Ferrocenyl Phosphine Ligand from Sugar: Applications in Rh-Catalyzed Asymmetric Hydrogenation Reactions.CHEMINFORM, Issue 17 2003Duan Liu Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Novel Monodentate Spiro Phosphorus Ligands for Rhodium-Catalyzed Hydrogenation Reactions.CHEMINFORM, Issue 28 2002Yu Fu Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] 1,4-Butanediol as a Reducing Agent in Transfer Hydrogenation ReactionsCHEMISTRY - AN ASIAN JOURNAL, Issue 3 2010Hannah Abstract 1,4-Butanediol is able to deliver two equivalents of H2 in hydrogen-transfer reactions to ketones, imines, and alkenes. Unlike simple alcohols, which establish equilibrium in the reduction of ketones, 1,4-butanediol acts essentially irreversibly owing to the formation of butyrolactone, which acts as a thermodynamic sink. It is therefore not necessary to use 1,4-butanediol in great excess in order to achieve reduction reactions. In addition, allylic alcohols are reduced to saturated alcohols through an isomerization/reduction sequence using a ruthenium catalyst with 1,4-butanediol as the reducing agent. Imines and alkenes are also reduced under similar conditions. [source] Cationic Iridium Complexes with Chiral Dithioether Ligands: Synthesis, Characterisation and Reactivity under Hydrogenation ConditionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005Leticia Flores-Santos Abstract A series of cationic IrI complexes containing chiral dithioether ligands have been prepared in order to study the influence of the sulfur substituents and the metallacycle size on the acetamidoacrylate hydrogenation reaction. In the case of complexes 6, 7 and 10, a mixture of diastereomers is observed in solution due to the sulfur inversion processes. In contrast, this fluxional behaviour is efficiently controlled by using bicyclic ligands which inhibit the S-inversion in complexes 8 and 9. The solid-state structure of complex 10b shows only one diastereomer with the sulfur substituents in a relative anti disposition and in an overall configuration of SCSCSSSS at the coordinated dithioether ligand. Iridium complexes containing seven- and six-membered metallacycles (6b,d, 7b,c, 10a,b) react with the substrate through S-ligand substitution, and the rate of this substitution is related to the position of the fluorine atom on the aromatic ring. On the contrary, complexes containing a bismetallacycle (8 and 9) are not displaced by the substrate. The catalytic hydrogenation activity of complexes 8 and 9 is analysed in terms of the high stability of the corresponding dihydride complexes (13 and 14). In both cases, only two of the four possible diastereomeric dihydride species are formed in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Development of Pharmaceutical Drugs, Drug Intermediates and Ingredients by Using Direct Organo-Click ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2008Dhevalapally B. Ramachary Abstract Here we report on our studies of the use of combinations of amino acids, amines, K2CO3 or Cs2CO3 and CuSO4/Cu for catalysing green cascade reactions. We aimed to prepare the highly reactive and substituted olefin species 7 and 8, under very mild and environmentally friendly conditions, thus giving the hydrogenated products 10 and 12 through the action of Hantzsch ester (4) by self-catalysis through decreasing the HOMO,LUMO energy gaps between olefins 7/8 and Hantzsch ester (4) through biomimetic reductions. Highly useful compounds 10 to 14 were assembled from simple substrates such as aldehydes 1, ketones 2, CH acids 3, Hantzsch ester (4) and alkyl halides 5 by diversity-oriented green synthesis involving cascade olefination/hydrogenation (O/H), olefination/hydrogenation/alkylation (O/H/A) and hydrogenation/olefination/hydrogenation (H/O/H) reaction sequences in one-pot fashion with stereospecific organo- and organo-/metal-carbonate catalysis. Highly functionalized diverse compounds such as 10 to 14 are biologically active products and have found wide applications as pharmaceutical drugs, drug intermediates and drug ingredients. For the first time in organocatalysis, we report the O/H/A/TE reaction to furnish high yields of transesterification products 11 by simply mixing the reactants under proline/K2CO3 catalysis conditions. Additionally, a novel organocatalytic H/O/H reaction sequence for the synthesis of alkyl-substituted aromatics has been developed. Furthermore, for the first time we have developed organocatalysed cascade olefination/hydrogenation/hydrolysis (O/H/H) reactions to furnish highly useful materials such as 2-oxochroman-3-carboxylic acid (14kc) and 2-amino-4H -chromene-3-carbonitrile (14kj) in good yields. Experimentally simple and environmentally friendly organocatalytic two-carbon homologation through cascade O/H/H reactions of aldehydes 1, Meldrum's acid (3c), Hantzsch ester (4) and acetic acid/triethylamine in ethanol has been demonstrated. Additionally, we have developed a green synthesis of the highly substituted 1,2,3-triazole 17 from simple substrates through a two-step combination of olefination/hydrogenation/alkylation and Huisgen cycloaddition reaction sequences under stereospecific organocopper catalysis conditions. In this paper we have found strong support for our hypothesis that, "decreasing the HOMO,LUMO energy gap between olefins 7/8 and Hantzsch ester (4) will drive the biomimetic hydrogenation reaction by self-catalysis". This self-catalysis was further confirmed with many varieties of examples.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Chirality Transfer in Imidazolium Camphorsulfonate Ionic Liquids through Ion Pairing EffectsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Karola Schneiders Abstract The paper describes our studies on ion pair interactions in ionic liquids (IL) using an asymmetric hydrogenation reaction as probe. Three different ionic liquids carrying prochiral keto-functionalized cations were hydrogenated in the presence of their chiral, enantiomerically pure counter-ion using an achiral heterogeneous ruthenium catalyst. For the hydrogenation of N -(3,-oxobutyl)- N -methylimidazolium camphorsulfonate (2), N -(3,-oxobutyl)imidazolium camphorsulfonate (4) and N -(5,-oxohexyl)- N -methylimidazolium camphorsulfonate (6) we found a strong dependency of the enantiomeric excess (ee in the cation) on the polarity of the solvent, the concentration of the IL and the structure of the IL. The highest ee values of up to 94% were found for the hydrogenation of 2 in ethanol. Interestingly, we observed that the ee (and consequently the strength of ion pair interaction) had a pronounced maximum for a certain concentration of the IL in the solvent depending on the nature of the solvent and on the substrate. Remarkably, the concentration leading to the maximum ee could be rationalized by independent determination of the degree of dissociation which was obtained by a combination of diffusion-ordered NMR spectroscopy and conductivity measurements. [source] Investigation of multiphase hydrogenation in a catalyst-trap microreactorJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2009S. McGovern BACKGROUND: Multiphase hydrogenation plays a critical role in the pharmaceutical industry. A significant portion of the reaction steps in a typical fine chemical synthesis are catalytic hydrogenations, generally limited by resistances to mass and heat transport. To this end, the small-scale and large surface-to-volume ratios of microreactor technology would greatly benefit chemical processing in the pharmaceutical and other industries. A silicon microreactor has been developed to investigate mass transfer in a catalytic hydrogenation reaction. The reactor design is such that solid catalyst is suspended in the reaction channel by an arrangement of catalyst traps. The design supports the use of commercial catalyst and allows control of pressure drop across the bed by engineering the packing density. RESULTS: This paper discusses the design and operation of the reactor in the context of the liquid-phase hydrogenation of o-nitroanisole to o-anisidine. A two-phase ,flow map' is generated across a range of conditions depicting three flow regimes, termed gas-dominated, liquid-dominated, and transitional, all with distinctly different mass transfer behavior. Conversion is measured across the flow map and then reconciled against the mass transfer characteristics of the prevailing flow regime. The highest conversion is achieved in the transitional flow regime, where competition between phases induces the most favorable gas,liquid mass transfer. CONCLUSION: The results are used to associate a mass transfer coefficient with each flow regime to quantify differences in performance. This reactor architecture may be useful for catalyst evaluation through rapid screening, or in large numbers as an alternative to macro-scale production reactors. Copyright © 2008 Society of Chemical Industry [source] Synthesis of Microporous Carbon Foams as Catalyst SupportsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2010F. Glenk Abstract Microporous carbon foams were synthesized as structured catalyst supports by the carbide-derived carbon (CDC) method. The self-supporting foams showed a narrow pore size distribution which seems to induce shape-selective effects during reactions. The applicability of these materials as supports for active metals was tested in a hydrogenation reaction of different olefins with a CDC powder wet impregnated with platinum. [source] Chiral amino amides for the ruthenium(II)-catalyzed asymmetric transfer hydrogenation reaction of ketones in waterCHIRALITY, Issue 1 2010Jincheng Mao Abstract The chiral amino amide 3 was derived from L -proline and used for the [RuCl2(p -cymene)]2 -catalyzed asymmetric transfer hydrogenation of prochiral ketones performed in water. Moderate to good chemical selectivities (up to 95% yield) and enantioselectivities (up to 90% ee) were obtained in the presence of 2 mol % of TBAB (n -Bu4NBr) as the phase transfer catalyst. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] Application of supercritical fluid extraction to regenerate spent Pd-active carbon catalystENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 4 2007Lidia D Abstract Pd-active carbon-type catalysts are used in a wide variety of processes, typical examples of which are liquid-phase hydrogenation reactions. In the case of these catalysts, a loss of their catalytic activity is observed. The aim of the present work was to assess the possibility of regenerating spent Pd/AC catalysts using supercritical fluid extraction. The following Pd/AC catalyst samples were investigated and compared: a commercial 10 wt % Pd catalyst (Aldrich) (denoted by CC), a spent catalyst (SC), SC subjected to supercritical fluid,CO2 extraction (SC/SFE/C), SC subjected to supercritical fluid,CO2,ethanol extraction (SC/SFE/C-Et), and SC subjected to supercritical fluid,ethane,propane extraction (SC/SFE/E-P). The last three catalysts were additionally subjected to heating in a hydrogen atmosphere at 410 K for 3 h. These were denoted by SC/SFE/C/H, SC/SFE/C-Et/H, and SC/SFE/E-P/H, respectively. The spent Pd/AC catalyst (SC) consists of mixed CC samples used in the reduction with hydrogen of various organic compounds. The catalysts CC, SC/SFE/C, SC/SFE/C/H, SC/SFE/C-Et/H, and SC/SFE/E-P/H were tested in the reduction of octanoylbenzene with hydrogen. The activity of the catalysts was estimated by measuring the reaction time and also the amount of hydrogen used in relation to the theoretical quantity required for the reaction. XPS and XRD methods were used to evaluate the changes occurring in the form of the palladium present on the Pd/AC catalyst surface during the regeneration processes. It was found that supercritical fluid-CO2 extraction followed by heating in a hydrogen atmosphere is the most effective method for regenerating that catalyst. The results of our investigations indicate that regeneration of a spent Pd/AC catalyst, irrespective of the reaction in which it has been used, should be based on the complete removal of byproducts, the purification of the catalyst surface, and the restoration of the original form of the palladium. The procedure proposed in this paper, i.e. SFE (CO2) and heating in H2, fulfils both the conditions mentioned above. © 2007 American Institute of Chemical Engineers Environ Prog, 2007 [source] A Palladium Wall Coated Microcapillary Reactor for Use in Continuous Flow Transfer HydrogenationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Christian Abstract Herein we describe the preparation of a novel continuous flow multi-channel microreactor in which the internal surface has been functionalised with a palladium coating, enabling its use in catalytic heterogeneous liquid-phase reactions. Simple chemical deposition techniques were used to immobilise palladium(0) on the channel wall surface of a polymeric multi-capillary extrudate made from ethylene-vinyl alcohol copolymer. The Pd coating of the microcapillaries has been characterised by mass spectrometry and light and electron microscopy. The functional activity of the catalytic Pd layer was tested in a series of transfer hydrogenation reactions using triethylsilane as the hydrogen source. [source] Ruthenium ONO-Type Pincer Complex: Synthesis, Structural Characterization, and CatalysisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Yao Zhang Abstract A novel nitrone-based pincer ligand was developed by a single-step synthesis from N -(tert -butyl)hydroxylamine acetate and 2,6-pyridinedicarboxaldehyde. The developed ligand allowed us to synthesize a cationic ruthenium pincer complex. A distorted octahedral coordination environment around the ruthenium center was observed. The complex showed excellent catalytic activity in transfer hydrogenation reactions with turnover numbers up to 590,000. [source] Triphase Hydrogenation Reactions Utilizing Palladium-Immobilized Capillary Column Reactors and a Demonstration of Suitability for Large Scale SynthesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 15 2005Juta Kobayashi Abstract We have developed a practical and highly productive system for hydrogenation reactions utilizing capillary column reactors, which occupy less space than ordinary batch systems, are low cost and easy to handle, and show feasibility toward large-scale chemical synthesis. Palladium-containing micelles were immobilized onto the inner surface of the capillaries. Nine palladium-immobilized capillaries were assembled and connected to a T-shaped connector, and hydrogen and a substrate solution were fed to capillaries via the connector. Hydrogenation of 1-phenyl-1-cyclohexene (1) proceeded smoothly to give phenylcyclohexane in quantitative yield. The capillaries themselves occupy only ca. 0.4,mL and a high space-time yield has been achieved (124.3,mg/17,min/0.4,mL). In addition, leaching of palladium was not detected by ICP analysis after reactions. [source] Asymmetric Hydrogenations (Nobel Lecture 2001)ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2003William Abstract The start of the development of catalysts for asymmetric hydrogenation was the concept of replacing the triphenylphosphane ligand of the Wilkinson catalyst with a chiral ligand. With the new catalysts, it should be possible to hydrogenate prochiral olefins. Knowles and his co-workers were convinced that the phosphorus atom played a central role in this selectivity, as only chiral phosphorus ligands such as (R,R)-DIPAMP, whose stereogenic center lies directly on the phosphorus atom, lead to high enantiomeric excesses when used as catalysts in asymmetric hydrogenation reactions. This hypothesis was disproven by the development of ligands with chiral carbon backbones. Although the exact mechanism of action of the phosphane ligands is not incontrovertibly determined to this day, they provide a simple entry to a large number of chiral compounds. [source] 1H and 13C NMR assignments of all three isomeric o -fluoronaphthaldehydes and three o -fluorophenanthrene aldehydesMAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2010Carl A. Busacca Abstract Three isomeric o -fluoronaphthaldehydes, 9-fluorophenanthrene, and three previously unreported o -fluorophenanthrene aldehydes were analyzed in detail by multiple NMR techniques to provide unambiguous assignment of structures and resonances. The six aldehydes serve as the key starting materials for novel chiral ligands used in highly enantioselective rhodium-catalyzed asymmetric hydrogenation reactions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Preparation and structures of a series of phosphorus-free Nickel(II) diamine complexes and their applications in hydrogenation of acetophenoneAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2010Zilu Chen Abstract To develop economical and phosphorus-free catalysts for hydrogenation of ketones, three new complexes, [Ni(1R,2R -dpen)2(H2O)Cl]2Cl2· 2Et2O (1), [Ni(1R,2R -dpen)(phen)(CH3OH)2]Cl2·2CH3OH (2) and [Ni(1,8-dan)2(DMF)Cl]2Cl2· 3H2O (3), and three reported compounds, [Ni(opda)(phen)Cl2]·CH3OH (4), [Ni(opda)2Cl2] (5) and [Ni(1,2-dach)2]Cl2 (6), were prepared and the structures of new compounds were determined by single crystal X-ray diffraction analysis, in which 1R,2R -dpen, phen, 1,8-dan, opda and 1,2-dach denote 1R,2R -1,2-diphenylethylenediamine, 1,10-phenanthroline, 1,8-diaminonaphthalene, o -phenylenediamine and 1,2-diaminocyclohexane, respectively. The catalytic effects for hydrogenation of acetophenone of these compounds were tested. This revealed very poor or no catalytic effects of these complexes in transfer hydrogenation of acetophenone using isopropanol or HCOOHNEt3 as hydrogen source. However, they presented much better catalytic effects in ionic hydrogenation of acetophenone using H2 gas as hydrogen source with a dependence of the catalytic effects on the base used in the hydrogenation reactions. The complexes represent a kind of green hydrogenation catalyst, although the conversion in the hydrogenation reactions is not as high as expected. Copyright © 2010 John Wiley & Sons, Ltd. [source] New chiral phosphinite ligands with C2 -symmetric axis and their possible applications in Ru-catalyzed asymmetric transfer hydrogenationAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2010Murat Aydemir Abstract The new chiral ligands N,N,-bis-[(1R)-1-ethyl-2- O -(diphenylphosphinite)ethyl]ethanediamide, 1, and N,N,-bis-[(1S)-1-isobutyl-2- O -(diphenylphosphinite)ethyl]ethanediamide, 2, and the corresponding ruthenium complexes 3 and 4 were prepared and their structures were elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis. Following activation by NaOH, these chiral ruthenium complexes serve as catalyst precursors for the asymmetric transfer hydrogenation of acetophenone derivatives in iPrOH. The complexes 3 and 4 showed high catalytic activity but low selectivity in asymmetric transfer hydrogenation reactions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Homogeneous Stabilization of Pt Nanoparticles in Dendritic Core,Multishell Architectures: Application in Catalytic Hydrogenation Reactions and RecyclingCHEMCATCHEM, Issue 7 2010Juliane Keilitz Abstract Core,multishell architectures are a new approach to homogeneously stabilize metal nanoparticles for harsh conditions. Herein, we present the synthesis and stabilization of Pt nanoparticles in dendritic core,multishell polymers and their application in hydrogenation reactions. The successful recycling of the catalyst was demonstrated for the hydrogenation of methyl crotonate 1 and was either achieved by ultrafiltration or in a two-phase system for at least 14,cycles. Thereby, the total turnover number (TON) was increased to 22,000. In the recycling experiments, low metal leaching into the product (as low as 0.3,ppm) was detected. Additionally, the selective hydrogenation of isophorone 3 was investigated and selectivities of 99:1 for CC versus CO hydrogenation were achieved. [source] Asymmetric Hydrogenation with Highly Active IndolPhos,Rh Catalysts: Kinetics and Reaction MechanismCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2010Jeroen Wassenaar Abstract The mechanism of the IndolPhos,Rh-catalyzed asymmetric hydrogenation of prochiral olefins has been investigated by means of X-ray crystal structure determination, kinetic measurements, high-pressure NMR spectroscopy, and DFT calculations. The mechanistic study indicates that the reaction follows an unsaturate/dihydride mechanism according to Michaelis,Menten kinetics. A large value of KM (KM=5.01±0.16,M) is obtained, which indicates that the Rh,solvate complex is the catalyst resting state, which has been observed by high-pressure NMR spectroscopy. DFT calculations on the substrate,catalyst complexes, which are undetectable by experimental means, suggest that the major substrate,catalyst complex leads to the product. Such a mechanism is in accordance with previous studies on the mechanism of asymmetric hydrogenation reactions with C1 -symmetric heteroditopic and monodentate ligands. [source] Microwave-Assisted Cross-Coupling and Hydrogenation Chemistry by Using Heterogeneous Transition-Metal Catalysts: An Evaluation of the Role of Selective Catalyst HeatingCHEMISTRY - A EUROPEAN JOURNAL, Issue 43 2009Muhammed Irfan Abstract The concept of specific microwave effects in solid/liquid catalytic processes resulting from the selective heating of a microwave-absorbing heterogeneous transition-metal catalyst by using 2.45,GHz microwave irradiation was evaluated. As model transformations Ni/C-, Cu/C-, Pd/C-, and Pd/Al2O3 -catalyzed carbon,carbon/carbon,heteroatom cross-couplings and hydrogenation reactions were investigated. To probe the existence of specific microwave effects by means of selective catalyst heating in these transformations, control experiments comparing microwave dielectric heating and conventional thermal heating at the same reaction temperature were performed. Although the supported metal catalysts were experimentally found to be strongly microwave absorbing, for all chemistry examples investigated herein no differences in reaction rate or selectivity between microwave and conventional heating experiments under carefully controlled conditions were observed. This was true also for reactions that use low-absorbing or microwave transparent solvents, and was independent of the microwave absorbtivity of the catalyst support material. In the case of hydrogenation reactions, the stirring speed was found to be a critical factor on the mass transfer between gas and liquid phase, influencing the rate of the hydrogenation in both microwave and conventionally heated experiments. [source] Natural alkaloids and synthetic relatives as chiral templates of the Orito's reactionCHIRALITY, Issue 1 2010Emília Tálas Abstract The enantioselective hydrogenation of methyl or ethyl pyruvate over cinchona-platinum catalyst system (Orito's reaction) is one of the most intensively studied heterogeneous catalytic asymmetric hydrogenation reactions. Studies aiming at systematic changes of the chiral template have played a crucial role in creating hypotheses for the mechanism of Orito's reaction. It is very important to clarify which structural unit of the alkaloid takes part in the enantiodifferentiation, and learn about the role of the different structural units of chiral templates. In this article, we made an attempt to describe the behavior of natural alkaloids, their synthetic derivatives, and analogues as chiral templates in the heterogeneous catalytic asymmetric hydrogenation of activated ketones. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||