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Homogeneous Catalysts (homogeneous + catalyst)
Selected AbstractsA Homogeneous Catalyst for Reduction of Optically Active Esters to the Corresponding Chiral Alcohols without Loss of Optical PuritiesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Wataru Kuriyama Abstract A ruthenium complex was found to catalyze the hydrogen reduction of esters under mild and neutral conditions. A variety of optically active esters can be reduced to the corresponding alcohols in excellent yield without loss of their optical purity or causing undesirable side reactions. Hydrogen reduction needs such simple operations , reaction, concentration, and purification , that the violent quench step and extraction step, which accompany conventional sodium borohydride or lithium aluminum hydride reduction, can be omitted. [source] Recycling a Homogeneous Catalyst through a Light-Controlled Phase Tag,ANGEWANDTE CHEMIE, Issue 26 2010Guiyan Liu Die Löslichkeit eines Ruthenium-Carben-Komplexes mit einem lichtempfindlichen Nitrobenzospiropyran-Rest wird durch Bestrahlung verändert: Er wechselt reversibel zwischen neutralem (lipophilem) und ionischem (lipophobem) Zustand (siehe Schema; Mes=Mesityl). Dieser Komplex katalysiert Ringschluss-Metathesen und kann mehrfach wiederverwendet werden. [source] ChemInform Abstract: An All-Inorganic, Stable, and Highly Active Tetraruthenium Homogeneous Catalyst for Water Oxidation.CHEMINFORM, Issue 31 2008Yurii V. Geletii 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] Mono-, Bi- and Tridentate N-Heterocyclic Carbene Ligands for the Preparation of Transition-Metal-Based Homogeneous CatalystsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2009Rosa Corberán Abstract This microreview focuses on the preparation of homogeneous catalysts of group 8,11 metals containing N-heterocyclic carbene ligands. The current status of the design of mono-, bi- and tridentate NHC ligands is reviewed through the description of the authors' own work. The catalytic applications of such complexes include hydrogen-borrowing, C,C coupling, reduction of double bonds and C,H activation reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] ChemInform Abstract: Polyglycerol-Supported Co- and Mn-Salen Complexes as Efficient and Recyclable Homogeneous Catalysts for the Hydrolytic Kinetic Resolution of Terminal Epoxides and Asymmetric Olefin Epoxidation.CHEMINFORM, Issue 32 2008Maryam Beigi 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] ChemInform Abstract: Homoleptic Lanthanoid Amides as Homogeneous Catalysts for Alkyne Hydroamination and the Tishchenko Reaction.CHEMINFORM, Issue 12 2002Markus R. Buergstein 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] Polymer Fibers as Carriers for Homogeneous CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Michael Stasiak Abstract This paper describes a polymer fiber-based approach for the immobilization of homogeneous catalysts. The goal is to generate products that are free of catalysts which would be of great importance for the development of optoelectronic or pharmaceutical compounds. Electrospinning was employed to prepare the non-woven fiber assembly composed of polystyrene. The homogeneous catalyst scandium triflate was immobilized on the polystyrene fibers during electrospinning and on corresponding core shell fibers using a fiber template approach. An imino aldol and an aza-Diels,Alder model reaction were carried out with each fibrous catalytic system. This resulted in the immobilization of homogeneous catalysts in a polymer environment without loss of their catalytic activity and may even be enhanced when compared with reactions carried out in homogeneous solutions. [source] One-Step Surface Decoration of Poly(propyleneimines) (PPIs) with the Glyceryl Moiety: New Way for Recycling Homogeneous Dendrimer-Based CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Sébastien Balieu Abstract First to fifth generations of poly(propyleneimines) (PPIs) were reacted with glycerol carbonate yielding a new family of glycerol-decorated PPIs (GD-PPI). Owing to the presence of glyceryl units surrounding the PPI core, the high generation GD-PPI-5 can be successfully immobilized in a glycerol phase, thus offering a convenient route for possible utilization as a recyclable homogeneous catalyst. In this context, we show here that GD-PPI-5 can be used as a basic catalyst in the ring opening of epoxides with carboxylic acids in glycerol. The high affinity of GD-PPI-5 for the glycerol phase allowed us to (i) selectively extract the reaction products from the glycerol/GD-PPI-5 mixture and (ii) recycle the GD-PPI-5 catalyst. More generally, this work offers new tools for the convenient recycling of valuable but expensive dendrimers. [source] The Immobilization of Rhodium-4-(diphenylphosphino)-2- (diphenylphosphinomethyl)-pyrrolidine (Rh-PPM) Complexes: A Systematic StudyADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12-13 2006Benoît Pugin Abstract A modular toolbox for the immobilization of homogeneous catalysts to various supports is described. It consists of functionalized chiral diphosphines and three different linkers based on isocyanate chemistry and it is used to attach the 4-(diphenylphosphino)-2-(diphenylphosphinomethyl)-pyrrolidine (PPM) ligand to a large variety of soluble, swellable and non-swellable solid organic polymers and to silica gels. As model reaction the hydrogenation of acetamidocinnamic acid derivatives, catalyzed with high enantioselectivity was chosen. Besides information on the usefulness of a particular type of support for synthetic applications, the experiments were also designed to address the question how parameters such as solubility, swellability, cage or pore size and solvent affect the rate and enantioselectivity of an immobilized catalyst. Rhodium complexes of ligands attached to soluble polymers and inorganic supports achieved ees up to 95,% and turnover frequencies between 700 and 1400,h,1, very close to the values of the homogeneous Rh catalyst (ee 95,%, TOF 1320,h,1). Insoluble or strongly cross-linked organic polymers led to catalysts with lower enantioselectivity and activity. PPM ligands attached to water soluble dendrimer fragments allowed hydrogenation in water solution with ees up to 94,%, albeit with much lower activity compared to reactions in methanol with the homogeneous catalyst. [source] Ab initio energy calculations and macroscopic rate modeling of hydroformylation of higher alkenes by Rh-based catalystAICHE JOURNAL, Issue 12 2009Maizatul S. Shaharun Abstract Ab initio quantum chemical computations have been done to determine the energetics and reaction pathways of hydroformylation of higher alkenes using a rhodium complex homogeneous catalyst. Calculation of fragments of the potential energy surfaces of the HRh(CO)(PPh3)3 -catalyzed hydroformylation of 1-decene, 1-dodecene, and styrene were performed by the restricted Hartree-Fock method at the second-order MŘller-Plesset (MP2) level of perturbation theory and basis set of 6-31++G(d,p). Geometrically optimized structures of the intermediates and transition states were identified. Three generalized rate models were developed on the basis of above reaction path analysis as well as experimental findings reported in the literature. The kinetic and equilibrium parameters of the models were estimated by nonlinear least square regression of available literature data. The model based on H2 -oxidative addition fitted the data best; it predicts the conversion of all the alkenes quite satisfactorily with an average deviation of 7.6% and a maximum deviation of 13%. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Copolymerization of ethylene with 1-hexene over metallocene catalyst supported on complex of magnesium chloride with tetrahydrofuranJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2004Krystyna Czaja Abstract The study of ethylene/1-hexene copolymerization with the zirconocene catalyst, bis(cyclopentadienyl)zirconium dichloride (Cp2ZrCl2)/methylaluminoxane (MAO), anchored on a MgCl2(THF)2 support was carried out. The influence of 1-hexene concentration in the feed on catalyst productivity and comonomer reactivity as well as other properties was investigated. Additionally, the effect of support modification by the organoaluminum compounds [(MAO, trimethlaluminum (AlMe3), or diethylaluminum chloride (Et2AlCl)] on the behavior of the MgCl2(THF)2/Cp2ZrCl2/MAO catalyst in the copolymerization process and on the properties of the copolymers was explored. Immobilization of the Cp2ZrCl2 compound on the complex magnesium support MgCl2(THF)2 resulted in an effective system for the copolymerization of ethylene with 1-hexene. The modification of the support as well as the kind of organoaluminum compound used as a modifier influenced the activity of the examined catalyst system. Additionally, the profitable influence of immobilization of the homogeneous catalyst as well as modification of the support applied on the molecular weight and molecular weight distribution of the copolymers was established. Finally, with the successive self-nucleation/annealing procedure, the copolymers obtained over both homogeneous and heterogeneous metallocene catalysts were heterogeneous with respect to their chemical composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2512,2519, 2004 [source] Copolymerization of propylene with various higher ,-olefins using silica-supported rac -Me2Si(Ind)2ZrCl2JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2001Jun-Ting Xu Abstract The copolymerization of propylene with 1-hexene, 1-octene, 1-decene, and 1-dodecene was carried out with silica-supported rac -Me2Si(Ind)2ZrCl2 as a catalyst. The copolymerization activities of the homogeneous and supported catalysts and the microstructures of the resulting copolymers were compared. The activity of the supported catalyst was only one-half to one-eighth of that of the homogeneous catalyst, depending on the comonomer type. The supported catalyst copolymerized more comonomer into the polymer chain than the homogeneous catalyst at the same monomer feed ratio. Data of reactivity ratios showed that the depression in the activity of propylene instead of an enhancement in the activity of olefinic comonomer was responsible for this phenomenon. We also found that copolymerization with ,-olefins and supporting the metallocene on a carrier improved the stereoregularity and regioregularity of the copolymers. The melting temperature of all the copolymers decreased linearly with growing comonomer content, regardless of the comonomer type and catalyst system. Low mobility of the propagation chain in the supported catalyst was suggested as the reason for the different polymerization behaviors of the supported catalyst with the homogeneous system. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3294,3303, 2001 [source] Liquid phase mineralization of gel-type anion exchange resin by a hybrid process of Fenton dissolution followed by sonication and wet air oxidationASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009T. L. Gunale Abstract A hybrid process of Fenton dissolution followed by sonication and wet air oxidation (WAO), has been demonstrated to mineralize strongly basic anion exchange resin (gel type). The solid anion exchange resin beads could be dissolved in water by Fenton process wherein the copper-catalyzed hydrogen peroxide (H2O2) reaction makes the resin hydrophilic by the disintegration of polymer matrix. Sonication of the dissolved resin thus obtained made the waste stream more amenable to WAO. Parameters for Fenton dissolution and sonication were studied to aid effective mineralization by WAO. The kinetic studies of WAO were performed using copper sulfate (CuSO4) as the homogeneous catalyst, in the temperature range of 483,523 K. It is thus possible to address the disposal of solid ion exchange resin by the hybrid process, described here. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Glycerol Etherification over Highly Active CaO-Based Materials: New Mechanistic Aspects and Related Colloidal Particle FormationCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2008Agnieszka Abstract Glycerol is an attractive renewable building block for the synthesis of di- and triglycerols, which have numerous applications in the cosmetic and pharmaceutical industries. In this work, the selective etherification of glycerol to di- and triglycerol was studied in the presence of alkaline earth metal oxides and the data are compared with those obtained with Na2CO3 as a homogeneous catalyst. It was found that glycerol conversion increased with increasing catalyst basicity; that is, the conversion increases in the order: MgO Polyamide Synthesis from 6-Aminocapronitrile, Part 1: N -Alkyl Amide Formation by Amine Amidation of a Hydrolyzed NitrileCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2007Adrianus Abstract The synthesis of N -hexylpentanamide from a stoichiometric amount of pentanenitrile and hexylamine has been studied as a model reaction for the synthesis of nylon-6 from 6-aminocapronitrile. The reaction was carried out under mild hydrothermal conditions and in the presence of a homogeneous ruthenium catalyst. For the mild hydrothermal conditions the presence of hexylamine distinctively increases the nitrile hydrolysis compared to the nitrile hydrolysis in the absence of hexylamine. Amine-catalyzed nitrile hydrolysis mainly produces the N-substituted amide. A clear product development is observed, consisting of first the terminal amide formation and second the accumulation of N -hexylpentanamide. With a maximum conversion of only 80,% after 18,h, the nitrile hydrolysis rate at 230,°C is still much too low for nylon-6 synthesis. Ruthenium dihydride phosphine was therefore used as a homogeneous catalyst, which significantly increases the nitrile hydrolysis rate. At a temperature of 140,°C and with only 0.5,mol,% [RuH2(PPh3)4] a 60,% nitrile conversion is already reached within 2,h. Initially the terminal amide is the sole product, which is gradually converted into N -hexylpentanamide. The reaction has a high initial rate, however, for higher conversions a strong decrease in hydrolysis rate is observed. This is ascribed to product inhibition, which results from the equilibrium nature of the reaction. [source] Mono-, Bi- and Tridentate N-Heterocyclic Carbene Ligands for the Preparation of Transition-Metal-Based Homogeneous CatalystsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2009Rosa Corberán Abstract This microreview focuses on the preparation of homogeneous catalysts of group 8,11 metals containing N-heterocyclic carbene ligands. The current status of the design of mono-, bi- and tridentate NHC ligands is reviewed through the description of the authors' own work. The catalytic applications of such complexes include hydrogen-borrowing, C,C coupling, reduction of double bonds and C,H activation reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] A Highly Selective, Polymer-Supported Organocatalyst for Michael Additions with Enzyme-Like BehaviorADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Esther Alza Abstract A polymer-supported ,,,-diarylprolinol silyl ether displays catalytic activity and enantioselectivity comparable to the best homogeneous catalysts in the Michael addition of aldehydes to nitroolefins. Above all, the combination of polymer backbone, triazole linker, and catalytic unit confers to it an unprecedented substrate selectivity in favor of linear, short-chain aldehydes. [source] Backbone Diversity Analysis in Catalyst DesignADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2009Abstract We present a computer-based heuristic framework for designing libraries of homogeneous catalysts. In this approach, a set of given bidentate ligand-metal complexes is disassembled into key substructures ("building blocks"). These include metal atoms, ligating groups, backbone groups, and residue groups. The computer then rearranges these building blocks into a new library of virtual catalysts. We then tackle the practical problem of choosing a diverse subset of catalysts from this library for actual synthesis and testing. This is not trivial, since ,catalyst diversity' itself is a vague concept. Thus, we first define and quantify this diversity as the difference between key structural parameters (descriptors) of the catalysts, for the specific reaction at hand. Subsequently, we propose a method for choosing diverse sets of catalysts based on catalyst backbone selection, using weighted D-optimal design. The computer selects catalysts with different backbones, where the difference is measured as a distance in the descriptors space. We show that choosing such a D-optimal subset of backbones gives more diversity than a simple random sampling. The results are demonstrated experimentally in the nickel-catalysed hydrocyanation of 3-pentenenitrile to adiponitrile. Finally, the connection between backbone diversity and catalyst diversity, and the implications towards in silico catalysis design are discussed. [source] A Density Functional Study of Ethylene Insertion into the M-methyl (M = Ti, Zr) Bond for Different Catalysts, with a QM/MM Model for the Counterion, B(C6F5)3CH3,ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2002Kumar Vanka Single site homogeneous catalysts have been studied extensively in recent years as alternatives to traditional heterogeneous catalysts. The current theoretical study uses density functional theory to study the insertion process of the ethylene monomer into the titanium-carbon chain for contact ion-pair systems of the type [L1L2TiCH3 -,-CH3 -B(C6F5)3], where L1, L2, are Cp, NPH3, and other ligands. Different modes of approach cis and trans to the ,-CH3 bridge were considered. The counterion, B(C6F5)3CH3,, was modeled by QM/MM methods. The value of ,Htot,the total barrier to insertion,was found to be positive (in the range of 4,15 kcal/mol). The ability of the ancillary ligands, L1 and L2, to stabilize the ion-pair was found to be an important factor in determining the value of ,Htot. On replacing the titanium metal center with zirconium, the ,Htot values were found to be lowered (in the range of 2,9 kcal/mol), indicating that they would be better catalysts than their titanium analogues. The size of the ligands L1 and L2 was increased by replacing hydrogens in the ligands with tertiary butyl groups. The value of ,Htot was found to increase (in the range of 10,28 kcal/mol) in contrast to the simple systems, for both the cis and trans cases of approach, with the cis mode of approach giving lower values of ,Htot. Solvent effects were incorporated with cyclohexane (, = 2.023) as the solvent, and were found to have a minor influence, ±(0.5,1.5) kcal/mol) on the insertion barrier for all the cases studied. [source] The Immobilization of Rhodium-4-(diphenylphosphino)-2- (diphenylphosphinomethyl)-pyrrolidine (Rh-PPM) Complexes: A Systematic StudyADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 12-13 2006Benoît Pugin Abstract A modular toolbox for the immobilization of homogeneous catalysts to various supports is described. It consists of functionalized chiral diphosphines and three different linkers based on isocyanate chemistry and it is used to attach the 4-(diphenylphosphino)-2-(diphenylphosphinomethyl)-pyrrolidine (PPM) ligand to a large variety of soluble, swellable and non-swellable solid organic polymers and to silica gels. As model reaction the hydrogenation of acetamidocinnamic acid derivatives, catalyzed with high enantioselectivity was chosen. Besides information on the usefulness of a particular type of support for synthetic applications, the experiments were also designed to address the question how parameters such as solubility, swellability, cage or pore size and solvent affect the rate and enantioselectivity of an immobilized catalyst. Rhodium complexes of ligands attached to soluble polymers and inorganic supports achieved ees up to 95,% and turnover frequencies between 700 and 1400,h,1, very close to the values of the homogeneous Rh catalyst (ee 95,%, TOF 1320,h,1). Insoluble or strongly cross-linked organic polymers led to catalysts with lower enantioselectivity and activity. PPM ligands attached to water soluble dendrimer fragments allowed hydrogenation in water solution with ees up to 94,%, albeit with much lower activity compared to reactions in methanol with the homogeneous catalyst. [source] Reaction Kinetics of Soybean Oil Transesterification Using Heterogeneous Metal Oxide CatalystsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2007K. Singh Abstract Homogeneous acid or base catalysts dissolve fully in the glycerol layer and partially in the fatty acid methyl ester (biodiesel) layer in the triglyceride transesterification process. Heterogeneous (solid) catalysts, on the other hand, can prevent catalyst contamination making product separation much simpler. In the present work, the transesterification kinetics of five different solid catalysts with soybean oil is presented. It is found that heterogeneous catalysts require much higher temperatures and pressures to achieve acceptable conversion levels compared to homogeneous catalysts. Subsequent to preliminary investigations, transesterifications were conducted for selected high performance solid catalysts, i.e., MgO, CaO, BaO, PbO, and MnO2 in a high pressure reactor up to a temperature of 215,°C. The yield of the fatty acid methyl esters and the kinetics (rate constant and order) of the reaction are estimated and are compared for each catalyst. [source] Cu and Au Metal,Organic Frameworks Bridge the Gap between Homogeneous and Heterogeneous Catalysts for Alkene Cyclopropanation ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2010Avelino Corma Prof. Abstract The copper and gold metal,organic frameworks (MOFs) [Cu3(BTC)2(H2O)3]n, [Cu3(BTC)2] (BTC=benzene-1,3,5-tricarboxylate), and IRMOF-3-SI-Au are active and reusable solid catalysts for the cyclopropanation of alkenes with high chemo- and diastereoselectivities. This type of material gives better results than previous solid catalysts while working together with the homogeneous catalysts. These MOFs can help to bridge the gap between homogeneous and heterogeneous catalysis. [source] Polymer Fibers as Carriers for Homogeneous CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Michael Stasiak Abstract This paper describes a polymer fiber-based approach for the immobilization of homogeneous catalysts. The goal is to generate products that are free of catalysts which would be of great importance for the development of optoelectronic or pharmaceutical compounds. Electrospinning was employed to prepare the non-woven fiber assembly composed of polystyrene. The homogeneous catalyst scandium triflate was immobilized on the polystyrene fibers during electrospinning and on corresponding core shell fibers using a fiber template approach. An imino aldol and an aza-Diels,Alder model reaction were carried out with each fibrous catalytic system. This resulted in the immobilization of homogeneous catalysts in a polymer environment without loss of their catalytic activity and may even be enhanced when compared with reactions carried out in homogeneous solutions. [source] An Efficient Hybrid, Nanostructured, Epoxidation Catalyst: Titanium Silsesquioxane,Polystyrene Copolymer Supported on SBA-15CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2007Lei Zhang Abstract A novel interfacial hybrid epoxidation catalyst was designed with a new immobilization method for homogeneous catalysts by coating an inorganic support with an organic polymer film containing active sites. The titanium silsesquioxane (TiPOSS) complex, which contains a single-site titanium active center, was immobilized successfully by in-situ copolymerization on a mesoporous SBA-15-supported polystyrene polymer. The resulting hybrid materials exhibit attractive textural properties (highly ordered mesostructure, large specific surface area (>380,m2,g,1) and pore volume (,0.46,cm3,g,1)), and high activity in the epoxidation of alkenes. In the epoxidation of cyclooctene with tert -butyl hydrogen peroxide (TBHP), the hybrid catalysts have rate constants comparable with that of their homogeneous counterpart, and can be recycled at least seven times. They can also catalyze the epoxidation of cyclooctene with aqueous H2O2 as the oxidant. In two-phase reaction media, the catalysts show much higher activity than their homogeneous counterpart due to the hydrophobic environment around the active centers. They behave as interfacial catalysts due to their multifunctionality, that is, the hydrophobicity of polystyrene and the polyhedral oligomeric silsesquioxanes (POSS), and the hydrophilicity of the silica and the mesoporous structure. Combination of the immobilization of homogeneous catalysts on two conventional supports, inorganic solid and organic polymer, is demonstrated to achieve novel heterogeneous catalytic ensembles with the merits of attractive textural properties, tunable surface properties, and optimized environments around the active sites. [source]
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