|
| ||
|
|
||
Catalytic Behavior (catalytic + behavior)
Selected AbstractsChemInform Abstract: A New Aspect of Nickel-Catalyzed Grignard Cross-Coupling Reactions: Selective Synthesis, Structure, and Catalytic Behavior of a T-Shape Three-Coordinate Nickel(I) Chloride Bearing a Bulky NHC Ligand.CHEMINFORM, Issue 29 2010Satoshi Miyazaki 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] Exo- and Endocyclic Oxazolinyl,Phosphane Palladium Complexes: Catalytic Behavior in Allylic Alkylation Processes.CHEMINFORM, Issue 42 2004Delphine Franco Abstract For Abstract see ChemInform Abstract in Full Text. [source] Catalytic behavior of wool,Rh complex in asymmetric hydrogenation of 2-methyl furan,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3-5 2003Man He Abstract A Wool,Rh complex was prepared by the reaction of wool with RhCl3·3H2O in ethanol solution, and was found to be useful as a chiral catalyst for the asymmetric hydrogenation of 2-methyl furan to (S)-(+)-2-methyl tetrahydrofuran at 28,°C and under atmospheric hydrogen pressure. When an appropriate Rh content in the Wool,Rh complex was selected, the yield and optical yield amounted to 53.7 and 76.9%, respectively, and the Wool,Rh complex catalyst could be reused several times without any noticeable loss in its optical catalytic activity. Wool is a very cheap natural biopolymer ligand, and Wool,Rh complex is very easy to prepare, and it is a very active, enantioselective and stable chiral catalyst for asymmetric hydrogenation of 2-methyl furan. Copyright © 2003 John Wiley & Sons, Ltd. [source] Catalytic behaviors of silica-supported methylcellulose- L -phenyl alanine,platinum complexes in asymmetric hydrogenation of diacetone alcoholPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 3-4 2002Kai Huang Abstract A new chiral natural bio-polymer,metal complexe, silica-supported methylcellulose- L -phenyl alanine,platinum complex (SiO2 -MC- L -Phe,Pt) has been prepared by a very simple method, and the Pt complex has been found to be able to catalyze the asymmetric hydrogenation of diacetone alcohol to give (R)-(,)-2-methyl-2,4-pentandiol at room temperature and under atmospheric hydrogen pressure. The product and optical yields of 2-methyl-2,4-pentandiol amounted to 67.0 and 92.7%, respectively. The product and optical yields were remarkably affected by the Pt content in the complex, the kind of solvent and the reaction temperature. This catalyst was very stable and could be reused several times without any remarkable change in optical catalytic activity. Copyright © 2002 John Wiley & Sons, Ltd. [source] Catalytic behaviors of enzymes attached to nanoparticles: the effect of particle mobilityBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2003Hongfei Jia Abstract Nanoparticles provide an ideal remedy to the usually contradictory issues encountered in the optimization of immobilized enzymes: minimum diffusional limitation, maximum surface area per unit mass, and high effective enzyme loading. In addition to the promising performance features, the unique solution behaviors of the nanoparticles also point to a transitional region between the heterogeneous (with immobilized enzymes) and homogeneous (with soluble free enzymes) catalysis. The particle mobility, which is related to particle size and solution viscosity through Stokes-Einstein equation, may impact the reaction kinetics according to the collision theory. The mobility-activity relationship was examined through experimental studies and theoretical modeling in the present work. Polystyrene particles with diameters ranging from 110,1000 nm were prepared. A model enzyme, ,-chymotrypsin, was covalently attached to the nanoparticles up to 6.6 wt%. The collision theory model was found feasible in correlating the catalytic activities of particles to particle size and solution viscosity. Changes in the size of particles and the viscosity of reaction media, which all affect the mobility of the enzyme catalyst, evidently altered the intrinsic activity of the particle-attached enzyme. Compared to KM, kcat appeared to be less sensitive to particle size and viscosity. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng84: 406,414, 2003. [source] Carbosilane Dendrons Functionalized at Their Focal PointEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2005Román Andrés Abstract The Si,Ph bond of PhSi[(CH2)3SiMe2Bz]3 (5) is cleaved with triflic acid to give TfOSi[(CH2)3SiMe2Bz]3, which, in turn, reacts with triethylammonium chloride or potassium cyclopentadienide to give, respectively, ClSi[(CH2)3SiMe2Bz]3 (8) and (C5H5)Si[(CH2)3SiMe2Bz]3 (10). This strategy can be applied to the post-growth incorporation of nucleophiles to the focal point of carbosilane dendritic wedges. In this way, cyclopentadiene-functionalized dendritic wedges of second and third generation C5H5 -Gn -[(CH2)3SiMe2Bz]x (n = 2, x = 9, 11; n = 3, x = 27, 12) have been obtained starting from Ph-Gn -[(CH2)3SiMe2Bz]x (6, 7). The metallocenes [{(BzMe2SiCH2CH2CH2)3SiC5H4}2MCl2] (M = Ti, 14; Zr, 15) have also been obtained from 10 and their catalytic behavior in ethylene and propylene polymerization, using MAO as a cocatalyst, has been studied and compared to that of related non-dendritic complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Stable Platinum(0) Catalysts for Catalytic Hydrosilylation of Styrene and Synthesis of [Pt(Ar-bian)(,2 -alkene)] ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2003Jeroen W. Sprengers Abstract The use of alkenes and bidentate N-ligands in the platinum(0)-catalyzed hydrosilylation of styrene with triethylsilane has been evaluated. A number of bidentate N-ligands, phen, bpy, dafo, and phenyl-bian, were tested at various reaction temperatures using in situ formed catalysts with [Pt(nbe)3] as a precursor. The main conclusions are: (i) ligands, such as phen, which form stable platinum(0) complexes, give lower catalytic activities compared to the ligands which form less stable complexes; (ii) a small ligand effect is observed with dafo and phenyl-bian compared to [Pt(nbe)3], the precursor complex, displaying the lability of these ligands. The complex [Pt(nbe)3], that only has labile alkene ligands, is an active catalyst at low temperatures. At higher temperatures, the catalyst is no longer stable and a decrease in yield is observed. Several novel complexes have been synthesized: [Pt(m,m -(CF3)2 -C6H3 -bian)(tcne)], [Pt(m,m -(CF3)2 -C6H3 -bian)(ma)], [Pt(p -MeO-C6H4 -bian)(ma)], [Pt(p -MeO-C6H4 -bian)(dmfu)] and [Pt(phenyl-bian)(dmfu)]. Whereas the two [Pt(Ar-bian)(ma)] complexes are intrinsically more active than the two [Pt(Ar-bian)(dmfu)] complexes, the latter are much more stable, i.e. the nature of the alkene in these complexes is an important factor in determining their catalytic behavior. Compared to [Pt(Me-nq)(nbe)2], the two [Pt(Ar-bian)(dmfu)] complexes are much more stable resulting in significantly higher overall yields. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] The lipase/acyltransferase from Candida parapsilosisFEBS JOURNAL, Issue 6 2002Molecular cloning, characterization of purified recombinant enzymes Candida parapsilosis has been previously shown to produce a lipase (i.e. able to catalyze efficiently the hydrolysis of insoluble lipid esters such as triacylglycerols) that preferentially catalyses transfer reactions such as alcoholysis in the presence of suitable nucleophiles other than water, even in aqueous media with high (> 0.9) water thermodynamic activity. The present work describes the cloning and the overexpression of the gene coding for this enzyme. Two ORFs (CpLIP1 and CpLIP2) were isolated. The deduced 465-amino-acid protein sequences contained the consensus motif (G-X-S-X-G) which is conserved among lipolytic enzymes. Only one of the two deduced proteins (CpLIP2) contained peptide sequences obtained from the purified lipase/acyltransferase. Homology investigations showed that CpLIP2 has similarities principally with 11 lipases produced by C. albicans (42,61%) and the lipase A from Candida antarctica (31%) but not with the other lipases sequenced so far. Both CpLIP1 and CpLIP2 were expressed in Saccharomyces cerevisiae, but only CpLIP2 coded for an active protein. The substrate specificity and the catalytic behavior of purified recombinant CpLIP2, with or without a C-terminal histidine tag, were not changed compared to those of the native lipase. [source] Highly Active and Recyclable Heterogeneous Iridium Pincer Catalysts for Transfer Dehydrogenation of AlkanesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Zheng Huang Abstract Pincer-ligated iridium complexes have proven to be highly effective catalysts for the dehydrogenation and transfer-dehydrogenation of alkanes. Immobilization onto a solid support offers significant potential advantages in the application of such catalysts particularly with respect to catalyst separation and recycling. We describe three approaches toward such immobilization: (i) covalent attachment to a Merrifield resin, (ii) covalent bonding to silica via a pendant alkoxysilane group, and (iii) adsorption on ,-alumina (,-Al2O3), through basic functional groups on the para- position of the pincer ligand. The simplest of these approaches, adsorption on ,-Al2O3, is also found to be the most effective, yielding catalysts that are robust, recyclable, and comparable to or even more active than the corresponding species in solution. Spectroscopic evidence (NMR, IR) and studies of catalytic activity support the hypothesis that binding occurs at the para- substituent and that this has only a relatively subtle and indirect influence on catalytic behavior. [source] Surface properties and catalytic behavior of MoO3/SiO2 in esterification of acetic acid with ethanolJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2006Abd El-Aziz A Said Abstract A series of MoO3/SiO2 catalysts was prepared by an impregnation method with Mo loadings ranging from 1 to 50 wt%. The original and calcined samples at 400 °C were characterized by thermogravimetry (TG), differential thermogravimetry (DTG), differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infra-red (FTIR) spectroscopy, and nitrogen adsorption measurements. The surface acidity and basicity of the catalysts were investigated by the dehydration,dehydrogenation of isopropanol and the chemisorption of pyridine. The catalytic esterification of acetic acid with ethanol was carried out at 220 °C in a conventional fixed-bed reactor at 1 atm using air as a carrier gas. The results clearly revealed that silica,molybdena catalysts were active and selective towards the formation of ethyl acetate. Moreover, the catalyst containing 20 wt% MoO3 was the most active and selective one. The results emphasize the importance of the surface acid sites together with the specific surface area of the prepared catalyst, towards ester formation. Copyright © 2005 Society of Chemical Industry [source] Catalytic porous ceramic prepared in-situ by sol-gelation for butane-to-syngas processing in microreactorsAICHE JOURNAL, Issue 7 2009Nico Hotz Abstract In this study, a novel flow-based method is presented to place catalytic nanoparticles into a reactor by sol-gelation of a porous ceramic consisting of Rh/ceria/zirconia nanoparticles, silica sand, ceramic binder, and a gelation agent. This method allows for the placement of a liquid precursor containing the catalyst into the final reactor geometry without the need of impregnating or coating of a substrate with the catalytic material. The so generated foam-like porous ceramic shows properties highly appropriate for use as catalytic reactor material, e.g., reasonable pressure drop due to its porosity, high thermal and catalytic stability, and excellent catalytic behavior. To investigate the catalytic activity, microreactors containing this foam-like ceramic are employed for the production of hydrogen and carbon monoxide-rich syngas from butane. The effect of operating parameters such as the inlet flow rate on the hydrocarbon processing is analyzed and the limitation of the reactor by diffusion mass transport is investigated. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Performance study of heptane reforming in the dense ceramic membrane reactorsAICHE JOURNAL, Issue 1 2008Wenliang Zhu Abstract Heptane reforming was investigated in three dense ceramic membrane reactors, where the membranes were modified differently with reforming catalyst. Each reactor displayed distinctive catalytic behavior. The reactor with a bare membrane showed low catalytic activity and low oxygen permeation flux (JO2), but gave stable performance. The left two membranes reactors modified with catalyst both displayed shift processes at the preliminary stage of membrane reaction, not only in JO2 but also in the selectivity of all products. Moreover, the membrane reactor with more catalyst gave higher performance in the case of JO2 and CO selectivity. The observed shift phenomena are due to the activation of catalyst on the membrane surface, and the different amounts of catalyst produce different impaction on the membrane reactions. On the basis of the results in three membrane reactors, a reaction pathway of hydrocarbon reforming in dense ceramic membrane reactor is proposed. Being some different from combustion and reforming mechanism (CRR), hydrocarbon reforming in dense ceramic membrane reactor has its own characteristics. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Preparation of macroporous functionalized polymer beads by a multistep polymerization and their application in zirconocene catalysts for ethylene polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2003Chengbin Liu Abstract Macroporous functionalized polymer beads of poly(4-vinylpyridine- co -1,4-divinylbenzene) [P(VPy- co -DVB)] were prepared by a multistep polymerization, including a polystyrene (PS) shape template by emulsifier-free emulsion polymerization, linear PS seeds by staged template suspension polymerization, and macroporous functionalized polymer beads of P(VPy- co -DVB) by multistep seeded polymerization. The polymer beads, having a cellular texture, were made of many small, spherical particles. The bead size was 10,50 ,m, and the pore size was 0.1,1.5 ,m. The polymer beads were used as supports for zirconocene catalysts in ethylene polymerization. They were very different from traditional polymer supports. The polymer beads could be exfoliated to yield many spherical particles dispersed in the resulting polyethylene particles during ethylene polymerization. The influence of the polymer beads on the catalytic behavior of the supported catalyst and morphology of the resulting polyethylene was investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 873,880, 2003 [source] Triisobutylaluminum as cocatalyst for zirconocenes.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2001Abstract An investigation of the catalytic behavior of the dimethylated zirconocenes Me2SiCp*NtBuZrMe2 [Cp* = C5(CH3)4; 1Me], Me2SiCp2ZrMe2 (2Me), Cp2ZrMe2 (3Me), Ind2ZrMe2 (4Me), Me2SiInd2ZrMe2 (5Me), Et(2-MeInd)2ZrMe2 (6Me), and Me2Si(2-MeInd)2ZrMe2 (7Me) with the combined activator triisobutylaluminum (TIBA)/CPh3B(C6F5)4 (Al/Zr = 250; B/Zr = 1) in ethylene polymerizations at increased monomer pressures (5,11 bar, 30 °C) was carried out. Sterically opened zirconocenes in ternary catalysts gave rise to active species effective in the formation of low molecular weight polyethylenes (PEs). These active species tended to increase the PE molecular weight [1Me (2100) < 2Me (20,000) < 5Me (89,000) < 3Me (94,500)] under similar conditions. PE obtained with 4Me showed a bimodal gel permeation chromatography curve with a 64% peak area [weight-average molecular weight (Mw) = 43,000] and a 36% peak area (Mw = 255,000). The increase in sterical demands from the zirconocenes was also demonstrated by the reduction of the chain transfer to monomer, the reinsertion of vinyl-ended PE chains, and their ability for isomerization. These reactions were most pronounced for the zirconocenes 1Me and 2Me. The active species responsible for the formation of low molecular weight PEs deactivated quickly. The zirconocenes 6Me, 7Me, and (2-PhInd)2ZrMe2 (8Me) bearing substituent at the 2-position of the indenyl ring was activated with TIBA alone, yielding active species effective in ethylene and propylene polymerizations. PEs formed with 6Me,8Me complexes activated with TIBA had high molecular weights. An increase in the Al/Zr ratio in the catalytic system 8Me/TIBA from 50 to 300 led to an enhancement of the molecular weight of polypropylene (PP) samples from oligomeric products to an viscosity-average molecular weight of 220,000. The increase in the molecular weights of PPs with an increase in the propylene concentration was also observed. An analysis of the catalytic performance of the 8Me/TIBA system showed first-order dependency of the initial polymerization rates on the TIBA concentration and close to second-order dependency on propylene. The second-order dependency on the monomer concentration is explained in terms of the monomer participation in the initiation step of the polymerization reaction. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1915,1930, 2001 [source] Fluorenyl based syndiotactic specific metallocene catalysts structural features, origin of syndiospecificityMACROMOLECULAR SYMPOSIA, Issue 1 2004Abbas Razavi Abstract The stereochemistry of propylene insertion/propagation reactions with a variety of Cs symmetric fluorenyl- containing single site catalysts is discussed. Our recent results indicate that independent of the chemical composition of the ancillary ligand fragments, or nature of the transition metal, active sites with local Cs symmetry and enantiotopic coordination positions behave syndioselectively in the general context of chain migratory insertion mechanism. Perfect bilateral symmetry neither exists nor is required in these processes. In this context the mechanism of syndiospecific polymerization is revisited by taking into account the structural characteristics and catalytic behavior of the original metallocene based (,5 -C5H4 -CMe2 -,5 -C13H8) MCl2/ MAO; M = Zr (1), Hf (2) catalyst systems and new syndiotactic specific systems including (,5 -C5H4 -CPh2-,5-3,6-di-tBut-C13H6)ZrCl2 (3), ,1,,5 -(,Me2Si)(3,6-di-tBut-Flu)(t-ButN)MCl2/ MAO; M =Ti (4), Zr (5) and ,1,,5 -(,Me2Si)(2,7-di-tBut-Flu)(t-ButN)MCl2/ MAO; M = Ti (6), Zr (7). [source] Synthesis, structure characterization and catalytic activity of lanthanide complexes containing an ansa carbonous-bridged cyclopentadienyl,thienyl ligandAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 1 2009Xiaomin Xie Abstract A kind of new lanthanocene complex with an ansa carbonous-bridged cyclopentadienyl/aromatic heterocycle ligand was prepared and characterized. Based on the data of elemental analyses, MS and IR, they were presumed to be solvent-free complexes (cyclo-C4H3SCMe2C5H4)2LnCl [Ln = Er (1), Dd (2), Y (3), Sm (4)]. These complexes were effective for the polymerization of methyl methacrylate in the presence of co-catalyst. When AlEt3 and NaH (nanometric) were used as different co-catalysts, the lanthanocene complexes 1,4 showed different catalytic behavior. These differences resulted from the formation of different active species. The catalyst system (cyclo-C4H3SCMe2C5H4)2LnCl/NaH (nanometric) showed high catalytic activity (yield , 95% and M, > 105) in a short time at the ambient temperature. Copyright © 2008 John Wiley & Sons, Ltd. [source] Efficient Simultaneous Dry Removal of SO2 and NOx from Flue Gas over Copper-Based Catalytic MaterialsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5-6 2000Gabriele Centi The combined removal of SO2 (DeSOx) and NOx (DeNOx) from flue gas of power plants can be efficiently realized with a dry process using copper-based sorbent-catalysts which oxidize-adsorb SO2 in the form of an easily regenerable copper-sulphate and catalyze the reduction of NO in the presence of NH3/O2. This contribution reviews the results on this topic, discussing in particular the following main aspects: (i) Sorption and catalytic chemistry of the process, (ii) Development and features of the copper-based sorbent-catalyst. (iii) Optimization of the reaction conditions. (iv) Kinetic models of the sorption and catalytic behavior and role of the textural properties of the catalyst, (v) Flowsheet and economics of the process, (vi) Behavior in extended operations and life time cycles. The key features of the technology and its fields of application are also discussed. [source] Water-in-ionic liquid microemulsion-based organogels as novel matrices for enzyme immobilizationBIOTECHNOLOGY JOURNAL, Issue 8 2010Ioannis V. Pavlidis Abstract The use of water-in-ionic liquid microemulsion-based organogels (w/IL MBGs) as novel supports for the immobilization of lipase B from Candida antarctica and lipase from Chromobacterium viscosum was investigated. These novel lipase-containing w/IL MBGs can be effectively used as solid phase biocatalysts in various polar and non-polar organic solvents or ILs, exhibiting up to 4.4-fold higher esterification activity compared to water-in-oil microemulsion-based organogels. The immobilized lipases retain their activity for several hours at 70°C, while their half life time is up to 25-fold higher compared to that observed in w/IL microemulsions. Fourier-transform infrared spectroscopy data indicate that immobilized lipases adopt a more rigid structure, referring to the structure in aqueous solution, which is in correlation with their enhanced catalytic behavior observed. [source] Pt Nanoparticles Supported on Highly Dispersed Alumina Coated inside SBA-15 for Enantioselective HydrogenationCHEMCATCHEM, Issue 10 2010Hongna Wang Abstract A series of Al2O3@SBA-15 composites with different alumina loadings have been prepared using a solid-state grinding method. Various techniques, such as X-ray diffraction, N2,sorption, FT-IR spectroscopy, and NMR spectroscopy, are used to characterize their structures and acidity. The Al2O3@SBA-15 composites retain the mesostructure of the SBA-15 host and the alumina is highly dispersed and uniformly coated inside the mesopores. The Al2O3@SBA-15 composites serve as remarkable supports for Pt nanoparticles, which can be used as catalysts in the enantioselective hydrogenation of ethyl pyruvate. Both the Brřnsted acid sites that originate from the interface of Al2O3 and SBA-15 in the Al2O3@SBA-15 composites and the appropriate interaction of Pt nanoparticles with alumina coated inside the mesopores of SBA-15 can improve the catalytic behavior of Pt/Al2O3@SBA-15 catalysts. [source] Catalytic and Heating Behavior of Nanoscaled Perovskites under Microwave RadiationCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2008T. Krech Abstract Perovskite powders of the types La0.5Ca0.5AlyM1,yO3,, (y = 0,0.8), M = Fe, Cr, Mn, Co and LaxSr1,xMnyCo1,y (x = 0.5,1, y = 0,1) were prepared via a sol-gel route according to the modified Pechini method. Incineration of the resins was performed before final sintering at 1000,°C for 6,h. The phase composition of the samples was established by X-ray powder diffraction analysis, and the lattice parameters were calculated using Rietveld analysis. The shape and size of the particles were determined via scanning electron microscopy and the specific surface area of the powder perovskites was established by the BET method. The principal particles were ca. 100,nm in size and formed agglomerates larger than 1.0,,m. The composition of the perovskites was established by EDX analysis. Following this, the catalytic behavior was tested by means of total oxidation of propane. The catalytic performance was measured at atmospheric pressure with 3,g of catalyst in a fixed-bed quartz reactor (i.d. = 18,mm) under thermal-assisted and microwave-assisted conditions. Initial results show a strong dependence of the catalytic and heating behavior on the nature of the M-atom and its number of unpaired d-electrons as well as on the particle size and its specific surface area. No significant difference in the results could be detected from comparison of the two heating methods. [source] CO2 and SnII Adducts of N-Heterocyclic Carbenes as Delayed-Action Catalysts for Polyurethane SynthesisCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2009Bhasker Bantu Abstract Catalytic rivals: Both CO2 -protected tetrahydropyrimidin-2-ylidene-based N-heterocyclic carbenes (NHCs) and SnII -1,3-dimesitylimidazol-2-ylidene, as well as SnII -1,3-dimesitylimidazolin-2-ylidene complexes (example displayed), have been identified as truly latent catalysts for polyurethane (PUR) synthesis rivaling all existing systems both in activity and latency. A series of CO2 -protected pyrimidin-2-ylidenes as well as 1,3-dimesitylimidazol-2-ylidene and dimesitylimidazolin-2-ylidene complexes of SnII have been prepared. Selected single-crystal X-ray structures are reported. The new compounds were investigated for their catalytic behavior in polyurethane (PUR) synthesis. All compounds investigated showed excellent catalytic activity, rivaling the industrially most relevant catalyst dibutyltin dilaurate. Even more important, all compounds displayed pronounced latent behavior, in selected cases rivaling and exceeding the industrially relevant latent catalyst phenylmercury neodecanoate both in terms of latency and catalytic activity. This allows for creating one-component PUR systems with improved pot lifetimes. Pseudo-second-order kinetics were found for both CO2 -protected tetrahyropyrimidin-2-ylidenes and for [SnCl2(1,3-dimesityldihydroimidazol-2-ylidene)], indicating a fast pre-catalyst decomposition prior to polyurethane formation. 1,3-Di(2-propyl)tetrahydropyrimidin-2-ylidene was additionally found to be active in the cyclotrimerization of various isocyanates, offering access to a broad variability in polymer structure, that is, creating both urethane and isocyanurate moieties within the same polymer. [source] Acid,Base Bifunctional Catalysis of Silica,Alumina-Supported Organic Amines for Carbon,Carbon Bond-Forming ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2008Ken Motokura Dr. Abstract Acid,base bifunctional heterogeneous catalysts were prepared by the reaction of an acidic silica,alumina (SA) surface with silane-coupling reagents possessing amino functional groups. The obtained SA-supported amines (SA,NR2) were characterized by solid-state 13C and 29Si,NMR spectroscopy, FT-IR spectroscopy, and elemental analysis. The solid-state NMR spectra revealed that the amines were immobilized by acid,base interactions at the SA surface. The interactions between the surface acidic sites and the immobilized basic amines were weaker than the interactions between the SA and free amines. The catalytic performances of the SA,NR2 catalysts for various carbon,carbon bond-forming reactions, such as cyano-ethoxycarbonylation, the Michael reaction, and the nitro-aldol reaction, were investigated and compared with those of homogeneous and other heterogeneous catalysts. The SA,NR2 catalysts showed much higher catalytic activities for the carbon,carbon bond-forming reactions than heterogeneous amine catalysts using other supports, such as SiO2 and Al2O3. On the other hand, homogeneous amines hardly promoted these reactions under similar reaction conditions, and the catalytic behavior of SA,NR2 was also different from that of MgO, which was employed as a typical heterogeneous base. An acid,base dual-activation mechanism for the carbon,carbon bond-forming reactions is proposed. [source] Iron halide mediated atom transfer radical polymerization of methyl methacrylate with N -alkyl-2-pyridylmethanimine as the ligandJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2004Huiqi Zhang Abstract The controlled atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) catalyzed by iron halide/N -(n -hexyl)-2-pyridylmethanimine (NHPMI) is described. The ethyl 2-bromoisobutyrate (EBIB)-initiated ATRP with [MMA]0/[EBIB]0/[iron halide]0/[NHPMI]0 = 150/1/1/2 was better controlled in 2-butanone than in p -xylene at 90 °C. Initially added iron(III) halide improved the controllability of the reactions in terms of molecular weight control. The p -toluenesulfonyl chloride (TsC1)-initiated ATRP were uncontrolled with [MMA]0/[TsC1]0/[iron halide]0/[NHPMI]0 = 150/1/1/2 in 2-butanone at 90 °C. In contrast to the EBIB-initiated system, the initially added iron(III) halide greatly decreased the controllability of the TsC1-initiated ATRP. The ration of iron halide to NHPMI significantly influenced the controllability of both EBIB and TsC1-initiated ATRP systems. The ATRP with [MMA]0/[initiator]0/[iron halide]0/[NHPMI]0 = 150/1//1/2 provided polymers with PDIs , 1.57, whereas those with [iron halide]0/[NHPMI]0 = 1 resulted in polymers with PDIs as low as 1.35. Moreover, polymers with PDIs of approximately 1.25 were obtained after their precipitation from acidified methanol. The high functionality of the halide end group in the obtained polymer was confirmed by both 1H NMR and a chain-extenstion reaction. Cyclic voltammetry was utilized to explain the differing catalytic behaviors of the in situ -formed complexes by iron halide and NHPMI with different molar ratios. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4882,4894, 2004 [source] | ||||||||||||||||||||||||||||