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High Catalytic Activity (high + catalytic_activity)
Kinds of High Catalytic Activity Selected AbstractsChemInform Abstract: High Catalytic Activity of As-Synthesized, Ordered Porous Silicate,Quaternary Ammonium Composite for Knoevenagel Condensation.CHEMINFORM, Issue 1 2001Yoshihiro Kubota 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] Metal-Free and PdII -Promoted [2+3] Cycloadditions of a Cyclic Nitrone to Phthalonitriles: Syntheses of Oxadiazolines as well as Phthalamide,PdII and Dihydropyrrolyl-iminoisoindolinone,PdII Complexes with High Catalytic Activity in Suzuki,Miyaura Cross-Coupling ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2008Jamal Lasri Dr. Abstract The previously unknown reactions between phthalonitriles, 1,2-(CN)2(C6)R1R2R3R41 (1,a, R1=R2=R3=R4=H; 1,b, R1=R2=R4=H, R3=CH3; 1,c, R1=R4=H, R2=R3=Cl; 1,d, R1=R2=R3=R4=Cl; 1,e, R1=R2=R3=R4=F), and a cyclic nitrone, ,O+NCHCH2CH2CMe22, proceed under heating in a sealed tube to give phthalimides 3, 2-oxadiazolyl-benzonitriles 4 or ortho -bis(oxadiazolyl)tetrafluorobenzene 4,e,. In the presence of palladium(II) chloride, phthalonitriles 1 react with 2 at room temperature, to give bis(pyrrolidin-2-ylidene)phthalamide PdII complexes 5 via metal-promoted rupture of the NO bond of the oxadiazoline ring. The ketoimine ligands thus generated can be liberated from the metal by displacement with a diphosphine. Although the first [2+3] cycloaddition of 2 to 1 can occur in the absence of the metal to give the mono-cycloadducts 4, the second [2+3] coupling at the still-unreacted cyano group requires its activation by coordination to PdII, affording complexes 6 containing two ligated oxadiazolyl-benzonitriles. These ligands undergo either i) further cycloaddition with 2 to afford ultimately (upon rearrangement) the bis(pyrrolidinylidene)phthalamide complexes 5 or ii) NO bond cleavage in the oxadiazoline ring with intramolecular attack of the imine nitrogen on the cyano carbon and bridging to a second PdII center to afford dimeric palladium(II) complexes 7, with chloride bridges, that bear a dihydropyrrolyl-iminoisoindolinone, a new type of ligand. The compounds were characterized by IR, 1H, and 13C,NMR spectroscopy, ESI MS or FAB+ MS, elemental analyses and, in the case of 4,c, 5,a, 5,c, and 7,c, also by X-ray diffraction analysis. Complexes 5,a and 7,c show high catalytic activity for the Suzuki,Miyaura cross-coupling reaction of bromobenzene and phenylboronic acid and give biphenyl in high yields with turnover frequencies (TOFs) of up to 9.0×105,h,1. [source] Kinetic Studies Prove High Catalytic Activity of a Diene,Rhodium Complex in 1,4-Addition of Phenylboronic Acid to ,,,-Unsaturated KetonesCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2006Asato Kina Abstract In the 1,4-addition of phenylboronic acid to ,,,-unsaturated ketones, [Rh(OH)(cod)]2 has a much higher catalytic activity than [Rh(OH)(binap)]2 (cod=1,5-cyclooctadiene, binap=2,2,-bis(diphenylphosphanyl)-1,1,-binaphthyl). Kinetic studies revealed that the rate-determining transmetalation step in the catalytic cycle has a large rate constant when [Rh(OH)(cod)]2 is used. [source] Facile, Efficient Copolymerization of Ethylene with Bicyclic, Non-Conjugated Dienes by Titanium Complexes Bearing Bis(,-Enaminoketonato) LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Jing-yu Liu Abstract Copolymerizations of ethylene with 5-vinyl-2-norbornene or 5-ethylidene-2-norbornene under the action of various titanium complexes bearing bis(,-enaminoketonato) chelate ligands of the type, [R1NC(R2)CHC(R3)O]2TiCl2 (1, R1=Ph, R2=CF3, R3=Ph; 2, R1=C6H4F- p, R2=CF3, R3=Ph; 3, R1=Ph, R2=CF3, R3=t- Bu; 4, R1=C6H4F- p, R2=CF3, R3=t- Bu; 5, R1=Ph, R2=CH3, R3=CF3; 6, R1=C6H4F- p, R2=CH3, R3=CF3), have been shown to occur with the regioselective insertion of the endocyclic double bond of the monomer into the copolymer chain, leaving the exocyclic vinyl double bond as a pendant unsaturation. The ligand modification strongly affects the copolymerization behaviour. High catalytic activities and efficient co-monomer incorporation can be easily obtained by optimizing the catalyst structures and polymerization conditions. [source] Kinetics and mechanisms of transalkylation and disproportionation of meta -diethylbenzene by triflic acid catalystINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2003S. M. Al-Zahrani The kinetics of transalkylation and isomerization of meta -diethylbenzene in the presence of benzene using triflic acid as a catalyst has been investigated. High catalytic activity of the triflic acid catalyst was observed in homogeneous liquid-phase reactions. On the basis of the product distribution obtained, transalkylation, disproportionation, and isomerization reactions have been considered and the main product of the reaction was ethylbenzene. These reactions are conducted in a closed liquid batch reactor with continuous stirring under dry nitrogen and atmospheric pressure over the temperature range of 288,308 K. The main transalkylation, disproportionation, and isomerization reactions occurred simultaneously and were considered as elementary reactions. The apparent activation energy of the transalkylation reaction was found to be 35.5 kJ/mol, while that of disproportionation reaction was 42.3 kJ/mol. The reproducibility of the experimental product distribution occurred with an average relative error of ±2%. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 555,563, 2003 [source] Cobalt and Nickel Complexes Bearing Pyrazolyliminophosphorane Ligands: Synthesis, Characterisation and Catalytic Ethylene Oligomerisation BehaviourEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2006Cheng Zhang Abstract Treatment of 1-(2,-azidophenyl)-3,5-dimethylpyrazole (1) with Ph2PR (R = Ph, Me) and (Ph2P)2CH2, respectively, affords the pyrazolyliminophosphoranes 2, 3 and 4. Reaction of 2 or 3 with [NiCl2(dme)] or NiBr2 yields the N,N-chelate nickel complexes 5,8, and with CoCl2 complexes 9 and 10. Reaction of 4 with [NiCl2(dme)], NiBr2 and CoCl2, respectively, affords the N,N,P-chelate complexes 11,13. Compounds 2,4 were characterised by 1H, 13C, 31P NMR and IR spectroscopy and elemental analysis, while complexes 5,13 were characterised by IR spectroscopy and elemental analysis. The structures of complexes 5, 9 and 12 were further characterised by single-crystal X-ray diffraction techniques. Complexes 5,13 are active catalysts for ethylene oligomerisation upon activation with alkylaluminium derivatives(Et2AlCl, MAO or MMAO). These complexes exhibit good to high catalytic activities (up to 3.54,×,106 g,mol,1,h,atm for the nickel complexes and 5.48,×,105 g,mol,1,h,atm for the cobalt complexes). The effects of varying ethylene pressure, temperature and aluminium co-catalyst/Ni or Co ratios with complexes 5, 9, 11 and 12 are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Recyclable Polymer- and Silica-Supported Ruthenium(II)-Salen Bis-pyridine Catalysts for the Asymmetric Cyclopropanation of OlefinsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Christopher Abstract Homogeneous ruthenium(II)-salen bis-pyridine complexes are known to be highly active and selective catalysts for the asymmetric cyclopropanation of terminal olefins. Here, new methods of heterogenization of these Ru-salen catalysts on polymer and porous silica supports are demonstrated for the facile recovery and recycle of these expensive catalysts. Activities, selectivities, and recyclabilities are investigated and compared to the analogous homogeneous and other supported catalysts for asymmetric cyclopropanation reactions. The catalysts are characterized with a variety of methods including solid state cross-polarization magic-angle spinning (CP MAS) 13C and 29Si,NMR, FT-IR, elemental analysis, and thermogravimetric analysis. Initial investigations produced catalysts possessing high selectivities but decreasing activities upon reuse. Addition of excess pyridine during the washing steps between cycles was observed to maintain high catalytic activities over multiple cycles with no impact on selectivity. Polymer-supported catalysts showed superior activity and selectivity compared to the porous silica-supported catalyst. Additionally, a longer, flexible linker between the Ru-salen catalyst and support was observed to increase enantioselectivity and diastereoselectivity, but had no effect on activity of the resin catalysts. Furthermore, the polymer-supported Ru-salen-Py2 catalysts were found to generate superior selectivities and yields compared to other leading heterogeneous asymmetric cyclopropanation catalysts. [source] Sulfobutyl Ether-,-Cyclodextrins: Promising Supramolecular Carriers for Aqueous Organometallic CatalysisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005Philippe Blach Abstract The potentialities of sulfobutyl ether-,-CDs derivatives as supramolecular carrier in a biphasic Tsuji,Trost reaction catalyzed by a water-soluble palladium complex of trisulfonated triphenylphosphine have been investigated. The efficiency of these cyclodextrins (CDs) strongly depends on the average molar substitution degree of cyclodextrin and the highest rate enhancements were obtained with cyclodextrins containing about 7 sulfobutyl ether groups. This result was attributed to the absence of a strong interaction between this cyclodextrin and the trisulfonated triphenylphosphine used to dissolve the catalyst in the aqueous phase and to the presence of an extended hydrophobic cavity allowing a better molecular recognition between the substrate and the cyclodextrin. This constitutes the first example of a non-interacting ,-cyclodextrin/phosphine couple with high catalytic activities. [source] Bis(,-enaminoketonato) vanadium (III or IV) complexes as catalysts for olefin polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2010Ji-Qian Wu Abstract Bis(,-enaminoketonato) vanadium(III) complexes (2a,c) [O(R1)CC(H)xC(R2)NC6H5]2VCl(THF) and the corresponding vanadium(IV) complexes (3a,c) [O(R1)CC(H)xC(R2) NC6H5]2VO (R1 = (CH2)4, R2 = H, x = 0, a; R1 = C6H5, R2 = H, x = 1, b; R1 = C6H5, R2 = C6H5, x = 1, c) have been synthesized from VCl3(THF)3 and VOCl2(THF)2, respectively, by treating with 2.0 equivalent ,-enaminoketonato ligands in tetrahydrofuran. Structures of 2b and 3a,c were further confirmed by X-ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2a,c and 3a,c exhibited high catalytic activities (up to 23.76 kg of PE/mmolV h bar), and afforded polymers with unimodal molecular weight distributions at 70 °C indicating the good thermal stability. The catalytic behaviors were influenced not only by the oxidation state of the catalyst precursors but also by the ligand structures. Complexes 2a,c and 3a,c were also effective catalyst precursors for ethylene/1-hexene copolymerization. The influence of polymerization parameters such as reaction temperature, Al/V molar ratio and hexene feed concentration on the ethylene/hexene copolymerization behaviors have bee also investigated in detail. In addition, the agents such as AlMe3, AliBu3, MeMgBr, MgCl2, and ZnEt2 were applied to control the molecular weight and molecular weight distribution modal. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3062,3072, 2010 [source] Ethylene polymerization and ethylene/hexene copolymerization with vanadium(III) catalysts bearing heteroatom-containing salicylaldiminato ligandsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2009Ji-Qian Wu Abstract A series of novel vanadium(III) complexes bearing heteroatom-containing group-substituted salicylaldiminato ligands [RNCH(ArO)]VCl2(THF)2 (Ar = C6H4, R = C3H2NS, 2a; C7H4NS, 2c; C7H5N2, 2d; Ar = C6H2tBu2 (2,4), R = C3H2NS, 2b) have been synthesized and characterized. Structure of complex 2c was further confirmed by X-ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et2AlCl. Complexes 2a,d exhibited high catalytic activities (up to 22.8 kg polyethylene/mmolV h bar), and affording polymer with unimodal molecular weight distributions at 25,70 °C in the first 5-min polymerization, whereas produced bimodal molecular weight distribution polymers at 70 °C when polymerization time prolonged to 30 min. The catalyst structure plays an important role in controlling the molecular weight and molecular weight distribution of the resultant polymers produced in 30 min polymerization. In addition, ethylene/hexene copolymerizations with catalysts 2a,d were also explored in the presence of Et2AlCl, which leads to the high molecular weight and unimodal distributions copolymers with high comonomer incorporation. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled over a wide range by the variation of catalyst structure and the reaction parameters, such as comonomer feed concentration, polymerization time, and polymerization reaction temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3573,3582, 2009 [source] Homopolymerizations and random copolymerizations of olefins with amino-substituted cyclopentadienylchromium complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2002Keiji Ogata Abstract 1-(2- N,N -Dimethylaminoethyl)-2,3,4,5-tetramethylcyclopentadienyl-chromium dichloride (1), (2- N,N -dimethylaminoethyl)cyclopentadienylchromium dichloride (6), and (2- N,N -dimethylaminoethyl)indenylchromium dichloride (7) in the presence of modified methylaluminoxane exhibit high catalytic activities for the polymerization of ethylene with random copolymerizations of ethylene with propylene, ethylene with 1-hexene, and propylene with 1-hexene. These initiators conduct polymerizations to give high molecular weight polymers with low polydispersities. However, the stereoregularities are very poor in these reactions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2759,2771, 2002 [source] Ethylene and propylene polymerization by the new substituted bridged (cyclopentadienyl)(fluorenyl) zirconocenesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 2 2006Xiaoxia Yang Abstract Eight Cs -symmetric complexes, R1R2C(Cp)(Flu)MCl2 [R1 = R2 = CH3CH2CH2, M = Zr (1), Hf (2); R1 = R2 = pCH3OC6H4, M = Zr (3), Hf (4); R1 = ptBuC6H4, R2 = Ph, M = Zr (5), Hf (6); R1 = R2 = ptBuC6H4, M = Zr (7); R1 = R2 = PhCH2, M = Zr (8)] have been synthesized and characterized. Zirconocenes all showed the same high catalytic activities in ethylene polymerization as complex Ph2C(Cp)(Flu)ZrCl2 (9). However, in the propylene polymerization, the catalytic activities decreased in the order 5 , 9 > 7 > 8. Introduction of tBu decreased the activities, probably due to the bulk steric hindrance. The polypropylene produced by 5 and 7 with tBu substituent showed a higher molecular weight (M,) than that produced by 9. The 13C NMR spectrum revealed the polymers from 7 and 8 to have shorter average syndiotactic block length than polymer produced by 9. It was noted that [mm] stereodefect of polypropylene by 8 could not be observed from 13C NMR, which showed that the benzyl on bridge carbon 8 prevented chain epimerization and enatiofacial misinsertion in polymerization. Copyright © 2005 John Wiley & Sons, Ltd. [source] Highly Dispersed Ruthenium Hydroxide Supported on Titanium Oxide Effective for Liquid-Phase Hydrogen-Transfer ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2008Kazuya Yamaguchi Dr. Abstract Supported ruthenium hydroxide catalysts (Ru(OH)x/support) were prepared with three different TiO2 supports (anatase TiO2 (TiO2(A), BET surface area: 316,m2,g,1), anatase TiO2 (TiO2(B), 73,m2,g,1), and rutile TiO2 (TiO2(C), 3.2,m2,g,1)), as well as an Al2O3 support (160,m2,g,1). Characterizations with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), and X-ray absorption fine structure (XAFS) showed the presence of monomeric ruthenium(III) hydroxide and polymeric ruthenium(III) hydroxide species. Judging from the coordination numbers of the nearest-neighbor Ru atoms and the intensities of the ESR signals, the amount of monomeric hydroxide species increased in the order of Ru(OH)x Evaluating Enzyme Cascades for Methanol/Air Biofuel Cells Based on NAD+ -Dependent EnzymesELECTROANALYSIS, Issue 7-8 2010Abstract Previous work by the group has entailed encapsulating enzymes in polymeric micelles at bioelectrode surfaces by utilizing hydrophobically modified Nafion membranes, which are modified in order to eliminate the harsh acidity of Nafion while tailoring the size of the polymer micelles to optimize for the encapsulation of an individual enzyme. This polymer encapsulation has been shown to provide high catalytic activity and enzyme stability. In this study, we employed this encapsulation technique in developing a methanol/air biofuel cell through the combined immobilization of NAD+ -dependent alcohol dehydrogenase (ADH), aldehyde dehydrogenase (AldDH) and formate dehydrogenase (FDH) within a tetrabutylammonium bromide (TBAB) modified Nafion to oxidize methanol to carbon dioxide with poly(methylene green) acting as the NADH electrocatalyst electropolymerized on the surface of the electrode. The methanol biofuel/air cell resulted in a maximum power density of 261±7.6,,W/cm2 and current density of 845±35.5,,A/cm2. This system was characterized for the effects of degree of oxidation, temperature, pH, and concentration of fuel and NAD. [source] The Effect of Surface Area and Crystal Structure on the Catalytic Efficiency of Iron(III) Oxide Nanoparticles in Hydrogen Peroxide DecompositionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2010Cenek Gregor Abstract Iron(II) oxalate dihydrate has been used as a readily decomposable substance for the controlled synthesis of nanosized iron(III) oxides. The polymorphous composition, particle size and surface area of these iron oxide nanoparticles were controlled by varying the reaction temperature between 185 and 500 °C. As-prepared samples were characterized by XRD, low-temperature and in-field Mössbauer spectroscopy, BET surface area and the TEM technique. They were also tested as heterogeneous catalysts in hydrogen peroxide decomposition. At the selected temperatures, the formed nanomaterials did not contain any traces of amorphous phase, which is known to considerably reduce the catalytic efficiency of iron(III) oxide catalysts. As the thickness of the sample (, 2 mm) was above the critical value, a temporary temperature increase ("exo effect") was observed during all quasi-isothermal decompositions studied, irrespective of the reaction temperature. Increasing the reaction temperature resulted in a shift of the exo effect towards shorter times and an increased content of maghemite phase. The maghemite content decreases above 350 °C as a result of a thermally induced polymorphous transition into hematite. The catalytic data demonstrate that the crystal structure of iron(III) oxide (i.e. the relative contents of maghemite and hematite) does not influence the rate of hydrogen peroxide decomposition. However, the rate constant increases monotonously with increasing sample surface area (and decreasing thermolysis temperature), reaching a maximum of 27,×,10,3 min,1(g/L),1 for the sample with a surface area of 285 m2,g,1. This rate constant is currently the highest reported value of all known iron oxide catalytic systems and is even slightly higher than that observed for the most efficient catalyst reported to date, which has a significantly larger surface area of 337 m2,g,1. This surprisingly high catalytic activity at relatively low surface area can be ascribed to the absence of a amorphous phase in the samples prepared in this study. Taking into account these new findings, the contributions of the key factors highlighted above (surface area, particle size, crystal structure, crystallinity) to the overall activity of iron oxides forhydrogen peroxide decomposition are discussed. [source] Structure,Catalytic Activity Relationship in Bridging Silacycloalkyl Ring Conformations of Constrained Geometry Titanium ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2008Eugene Kang Abstract A series of cyclic silylene-bridged (amidocyclopentadienyl)dichlorotitanium(IV) complexes [TiCl2{,5 -1-(CySitBuN- ,N)-2,3,4,5-R4 -C5}] was prepared, where CySi = silacyclobutyl (a), silacyclopentenyl (b), silacyclopentyl (c), and silacyclohexyl (d); R = H (4), Me (5). The starting silane, dichlorosilacycloalkane CySiCl2 (1), was treated with NaCp (LiCp*), followed by LiNHtBu to yield the cyclic silylene-bridged ligands (R4C5)CySi(NHtBu) [R = H (2); Me (3)]. Subsequent deprotonation with n -butyllithium, followed by transmetalation with TiCl4 yielded the desired constrained geometry complexes (CGCs) (CpCySiNtBu)TiCl2 (4) and (Cp*CySiNtBu)TiCl2 (5). The structures of the resulting cyclopentadienyl- (4b and 4c) and tetramethylcyclopentadienyl(silacycloalkyl)amidotitanium(IV) dichloride (5a, 5c, and 5d) species were studied by using X-ray crystallography to obtain geometrical information on cyclic silylene-modified CGCs. The ethylene polymerization by the cyclic silylene-bridged CGCs 4 and 5 was examined to verify the structure,catalytic activity relationship derived from variation of the size of a cyclic silylene ring. Indeed, the size of the cyclic silylene ring at the 1,1,-position of 4 and 5 affected the catalytic activities through the ethylene polymerization. Systematic increase in the catalytic activities was observed as the cyclic silylene-bridging unit was expanded from a four- to six-membered ring. In the present study, we found that CGCs of TiIV with a six-membered silylene-bridged ligand (5d) produced active catalytic species for the formation of polyethylene with Mw = 42.7,×,10,4 g,mol,1 and Mw/Mn = 2.1 with excellent catalytic activities (20.9 kg,polymer per mmol of Ti). When titanium(IV) dimethyl complex (6d) was applied in continuous polymerization process, impressive high catalytic activity on copolymerization with 1-octene was observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Facile Formation of Hexacyclic [Al3O2Cl] Aluminum and Alkoxide-Bridged Titanium Complexes: Reactions of AlMe3 with [Ti(L)Cl2] [L = 2,2,-Methylenebis(6- tert -butyl-4-methylphenolato)]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2007Dao Zhang Abstract The titanium dichloride complex [(L)TiCl2] [L = 2,2,-methylenebis(6- tert- butyl-4-methylphenolato)] (1) reacted with trimethylaluminum (AlMe3) in a 1:2 ratio to give a trimetallic aluminum complex of the composition [(L)(AlMe2)3(,-Cl)] (2) with a symmetric six-membered ring [Al3(,2 -O)2(,2 -Cl)] and a four-coordinate aluminum center in the solid state. The reaction of 1 equiv. AlMe3 gave [(L)TiMeCl] (3), which could absorb O2 gas to afford the oxygen-insertion product [{(L)TiCl}2(,-OMe)2] (4) with a five-coordinate metal center. Upon reaction of H2L with AlMe3, the binuclear, four-coordinate adduct [{(L)AlMe}2] (5) was formed. Complex 4 supported on MgCl2 and activated with aluminum alkyls reveals high catalytic activity for ethylene polymerization to produce polymers with molecular weight distributions of ca. 3.1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Functionalized Multi-Wall Carbon Nanotubes for Lipase Immobilization,ADVANCED ENGINEERING MATERIALS, Issue 5 2010I. V. Pavlidis Abstract We examine the immobilization of lipase B from Candida antarctica on functionalized multi-wall carbon nanotubes (MWCNTs) through physical adsorption. MWCNTs functionalized with carboxyl-, amine- and ester- terminal groups on their surface are used as immobilization carriers. Dispersion of the nanotubes and the immobilization procedure take place in aqueous and low-water media. High enzyme loadings are attained, up to 25% of the weight of the carbon nanotubes. These novel biomaterials are characterized though FT-IR and Raman spectroscopy. The MWCNT,lipase bioconjugates exhibit high catalytic activity and increased storage and operational stability. The biomaterials retain more than 55% of their initial activity after 6 months at 4,°C, while they retain approximately 25% of their initial activity after 30 d of incubation in hexane at 60,°C. The catalytic behaviour of the immobilized enzyme depends on the terminal group of the carbon nanotubes, the concentration of the enzyme and the immobilization method employed. [source] Synthesis of ,-Amino Nitriles from Carbonyl Compounds, Amines, and Trimethylsilyl Cyanide: Comparison between Catalyst-Free Conditions and the Presence of Tin Ion-Exchanged MontmorilloniteEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2010Jiacheng Wang Abstract In the absence of catalysts, the three-component, one-pot synthesis of ,-amino nitriles proceeded using various aldehydes and ketones together with amines and trimethylsilyl cyanide (TMSCN) in high yields under neat conditions at room temperature. The addition order of the reagents had a significant influence on the yields of the desired ,-amino nitriles. In contrast, when tin ion-exchanged montmorillonite (Sn-Mont), prepared by the ion-exchange of sodium montmorillonite (Na-Mont) with a tin tetrachloride solution, was used as a catalyst, the reaction rates significantly increased compared with those without catalysts, and the range of the applicable carbonyl compounds was also extended: structurally diverse aromatic, aliphatic and heteroatom-containing carbonyl compounds, including sterically hindered ketones as well as aliphatic and aromatic amines, were converted into the desired ,-amino nitriles in good to excellent yields with short reaction times under mild conditions. Sn-Mont showed a better catalytic activity than proton or other metal ion-exchanged montmorillonites, supported SnO2 catalysts and the previously reported homogeneous or heterogeneous catalysts. The recovered catalyst was reused several times without loss of catalytic performance. Along with the expansion of the interlayer space of Sn-Mont, the strong Brønsted acid and Lewis acid nature of Sn-Mont derived from protons and SnO2 nanoparticles present in the interlayers of Sn-Mont likely played important and cooperative roles in the high catalytic activity. [source] Reactive Template Method to Synthesize Gold Nanoparticles with Controllable Size and Morphology Supported on Shells of Polymer Hollow Microspheres and Their Application for Aerobic Alcohol Oxidation in WaterADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Jie Han Abstract A novel method has been developed to synthesize gold nanoparticles with tunable size and morphology supported on both inner and outer surfaces of poly(o -phenylenediamine) (PoPD) hollow microspheres, which act as both reductant and template/stabilizer. The size of gold nanoparticles supported on shells of PoPD hollow microspheres can be tuned from 3 to 15,nm by changing the concentration of the gold source, HAuCl4. Gold nanorods supported on shells of PoPD hollow microspheres can also be fabricated by introducing a well-known seed-growth strategy. In addition, silver nanoparticles supported on shells of PoPD hollow microspheres can also be successfully fabricated using the same strategy, which indicates the diversity of this proposed method for polymer hollow microspheres supporting noble metal nanoparticles. The products are characterized by X-ray diffraction and contact angle analysis. Furthermore, the catalytic activity of the obtained PoPD-microsphere-supported gold nanoparticles for aerobic alcohol oxidation is investigated. The results demonstrate that such polymer-supported gold nanoparticles can be used as reusable catalysts with high catalytic activity for aerobic alcohol oxidation in water. [source] Highly Enantioselective Iridium-Catalyzed Hydrogenation of Trisubstituted Olefins, ,,,-Unsaturated Ketones and Imines with Chiral Benzylic Substituted P,N LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Wei-Jing Lu Abstract The benzylic substituted P,N ligands, diphosphinobenzyloxazolines, showed their high catalytic activity as well as asymmetric induction in the iridium-catalyzed asymmetric hydrogenation of unfunctionalized alkenes, ,,,-unsaturated esters, allyl alcohols, ,,,-unsaturated ketones, and imines, providing the corresponding chiral products in high ee with high conversion. [source] Highly Efficient and Selective Synthesis of (E)-,,,-Unsaturated Ketones by Crossed Condensation of Ketones and Aldehydes Catalyzed by an Air-Stable Cationic Organobismuth PerfluorooctanesulfonateADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Renhua Qiu Abstract An air-stable cationic organobismuth perfluorooctanesulfonate possessing both acidic and basic characters was synthesized, and showed high catalytic activity, diastereoselectivity, stability, and reusability in the one-pot synthesis of (E)-,,,-unsaturated ketones through highly selective crossed condensation of ketones and aldehydes in water. [source] "Click" Polymer-Supported Palladium Nanoparticles as Highly Efficient Catalysts for Olefin Hydrogenation and Suzuki Coupling Reactions under Ambient ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Cátia Ornelas Abstract Complexation of palladium(II) acetate [Pd(OAc)2] or dipotassium tetrachloropalladate [K2PdCl4] to "click" polymers functionalized with phenyl, ferrocenyl and sodium sulfonate groups gave polymeric palladium(II)-triazolyl complexes that were reduced to "click" polymer-stabilized palladium nanoparticles (PdNPs). Transmission electron microscopy (TEM) showed that reduction using sodium borohydride (NaBH4) produced PdNPs in the 1,3,nm range of diameters depending on the nature of the functional group, whereas slow reduction using methanol yielded PdNPs in the 22,25,nm range. The most active of these PdNPs (0.01% mol Pd), stabilized by poly(ferrocenyltriazolylmethyl)styrene, catalyzed the hydrogenation of styrene at 25,°C and 1 atm hydrogen, with turnover numbers (TONs) of 200,000. When stabilized by the water-soluble poly(sodium sulfonate-triazolylmethyl)styrene, the PdNPs (0.01% mol Pd) catalyze the Suzuki,Miyaura coupling between iodobenzene (PhI) and phenylboronic acid [PhB(OH)2] in water/ethanol (H2O/EtOH) at 25,°C with TONs of 8,200. This high catalytic activity is comparable to that obtained with "click" dendrimer-stabilized PdNPs under ambient conditions. [source] Lanthanide Bis[(trifluoromethyl)sulfonyl]imides as Reusable Catalysts for Mononitration of Substituted Benzenes in Ionic LiquidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Shuojin Wang Abstract Lanthanide bis[(trifluoromethyl)sulfonyl]imides as a kind of effective catalyst were used in quaternary ammonium ionic liquids to afford a useful new method for the nitration of substituted benzenes with concentrated nitric acid (95%) as nitrating agent. The less expensive lanthanum bis[(trifluoromethyl)sulfonyl]imide was found to be the most effective catalyst employed in the ionic liquid tributylammonium bis[(trifluoromethyl)sulfonyl]imide. The lanthanum bis[(trifluoromethyl)sulfonyl]imide/tributylammonium bis[(trifluoromethyl)sulfonyl]imide system demonstrated high catalytic activity for the nitration of halobenzenes and rendered good to excellent yields. This catalyst/ionic liquid system could be recovered by simple procedures and recycled for at least 5 times. [source] Towards Continuous Flow, Highly Enantioselective Allylic Amination: Ligand Design, Optimization and SupportingADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Dana Popa Abstract A family of enantiopure diphenylphosphinooxazolines (PHOX) containing in their structures a sterically tunable alkoxymethyl group (-CH2OR) has been optimized for the palladium-catalyzed asymmetric allylic amination. The optimal catalyst (R=CH3), depicting very high catalytic activity and broad scope applicability, has been further modified to include an ,-alkynyloxy substituent of variable length for polymer supporting via click chemistry, and has been anchored onto slightly cross-linked azidomethyl poly(styrene). The length of a polymethylene chain connecting the PHOX unit with the 1,2,3-triazole linker has been optimized, and the first polymer-supported PHOX ligands for the highly enantioselective allylic amination have been prepared in this manner. Conditions for catalyst recovery and reuse in microwave-promoted amination reactions have been established, and the system has been finally adapted to continuous flow operation. [source] Highly Active, Well-Defined (Cyclopentadiene)(N-heterocyclic carbene)palladium Chloride Complexes for Room-Temperature Suzuki,Miyaura and Buchwald,Hartwig Cross-Coupling Reactions of Aryl Chlorides and Deboronation Homocoupling of Arylboronic AcidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Zhong Jin Abstract A new class of well-defined N-heterocyclic carbene (NHC)-(cyclopentadiene)palladium chloride complexes such as CpPd(NHC)Cl wasw synthesized from the readily available starting NHC-palladium(II) chloride dimers. These air-stable, coordinatively saturated NHC-Pd complexes bearing the cyclopentadiene (Cp) unit exhibit high catalytic activity in the room temperature Suzuki,Miyaura and Buchwald,Hartwig cross-coupling reactions involving unactive aryl chlorides as the substrates. In addition, they are found to be extremely efficient catalysts in the deboronation homocoupling of arylboronic acids at room temperature. [source] Copper Nanoparticles on Charcoal for Multicomponent Catalytic Synthesis of 1,2,3-Triazole Derivatives from Benzyl Halides or Alkyl Halides, Terminal Alkynes and Sodium Azide in Water as a "Green" SolventADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Hashem Sharghi Abstract A one-pot procedure for synthesis of 1,2,3-triazole derivatives via the three-component coupling (TCC) reaction between terminal alkynes, benzyl or alkyl halides, and sodium azide in the presences of 1,mol% nanoparticles copper/carbon (Cu/C) catalyst has been developed. The catalyst showed high catalytic activity and 1,4-regioselectivity for the [3+2],Huisgen cycloaddition in water as a "green" solvent and good to excellent yields were obtained in all cases. This procedure eliminates the need to handle organic azides, and they are generated in situ. The reaction has a broad scope and is especially practical for the synthesis of new azacrown ether and anthraquinone derivatives of triazole. The heterogeneous catalysts were fully characterized by scanning electron microscopy (SEM), atomic forced microscopy (AFM), X-ray diffraction (XRD), inductively coupled plasma (ICP) analysis and FT-IR experimental techniques. The catalyst was recycled ten times without significant loss of activity. [source] Enhanced Cooperativity in Hydrolytic Kinetic Resolution of Epoxides using Poly(styrene) Resin-Supported Dendronized Co-(Salen) CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2008Poorva Goyal Abstract Excellent enantioselectivities and isolated yields have been achieved for the hydrolytic kinetic resolution of epoxides using a resin-supported dendronized R,R-(salen)Co catalyst with catalyst loadings as low as 0.04 mol%, the lowest metal loadings of any heterogeneous resin-supported (salen)Co catalyst reported to date. In addition, the supported catalysts can be recycled and reused with comparable enantioselectivities. It is hypothesized that the high catalytic activity can be attributed to the flexible linker and the dendronized framework supporting the (salen)Co moieties on the resin thereby promoting cooperativity between two metal centers. This work opens up new opportunities for the design of highly active resin-supported catalysts that catalyze transformations through a bimetallic pathway. [source] Fluorapatite-Supported Palladium Catalyst for Suzuki and Heck Coupling Reactions of HaloarenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7 2007M. Lakshmi Kantam Abstract A fluorapatite-supported palladium catalyst (PdFAP) was synthesized by treatment of fluorapatite (prepared by incorporating the basic species fluoride ion into apatite in situ by co-precipitation) with bis(benzonitrile)palladium(II) chloride in acetone. The catalyst displayed high catalytic activity for Suzuki coupling of aryl iodides and bromides with boronic acids at room temperature and chloroarenes at 130,°C in the presence of tetrabutylammonium bromide to give biaryls in excellent yields. Heck olefination of chloroarenes was also successfully carried out by this catalyst. PdFAP was recovered quantitatively by simple filtration and reused with consistent activity. PdFAP was well characterized by XRD, FTIR, XPS, ICP-AES, CO2 TPD and CHN elemental analysis. [source] Synthesis of carvacrol by Friedel,Crafts alkylation of o -cresol with isopropanol using superacidic catalyst UDCaT-5JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 10 2009Ganapati D. Yadav Abstract BACKGROUND: Alkylation of o -cresol with propylene or isopropyl alcohol (IPA) over solid acid catalysts results in the formation of carvacrol, which finds potential applications in the synthesis of fine chemicals, intermediates, specialty chemicals, flavours and fragrances. RESULTS: The present work covers evaluation of novel mesoporous superacidic catalysts namely UDCaT-4, UDCaT-5 and UDCaT-6 in the greener synthesis of carvacrol. The catalysts are modified versions of zirconia showing high catalytic activity, stability and reusability. The catalytic activity increases in the following order: UDCaT-5 > UDCaT-4 > UDCaT-6 > sulfated zirconia. The process was optimized and a mathematical model developed to describe the reaction pathway in liquid phase. Carvacrol could be efficiently obtained with a selectivity up to 82% at an isopropanol conversion of 98% after 2 h over UDCaT-5 at 180 °C. CONCLUSION: The reaction is free from any external mass transfer as well as intraparticle diffusion limitations and is intrinsically kinetically controlled. An overall second-order kinetic equation was used to fit the experimental data. The activation energy was found to be 19.2 kcal/mol. The reaction was carried out without any solvent in order to make the process cleaner and greener. Copyright © 2009 Society of Chemical Industry [source]
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