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Alkoxides
Kinds of Alkoxides Terms modified by Alkoxides Selected AbstractsEnantioselective Silylcyanation of Aldehydes and Ketones by a Titanium Catalyst Prepared from a Partially Hydrolyzed Titanium Alkoxide and a Schiff Base LigandADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Kazuhiko Yoshinaga Abstract In the presence of small amount (0.2,1.0 mol%) of a titanium complex catalyst prepared from a partially hydrolyzed titanium alkoxide and an optically active tridentate Schiff base ligand, the enantioselective silylcyanation of aldehydes and ketones proceeded in a short reaction time at room temperature to afford the corresponding optically active cyanohydrin derivatives in excellent chemical yield with high enantiomeric excess (86,97% ee). The results indicate that partially hydrolyzed titanium alkoxides are a promising titanium source for the preparation of efficient catalysts for asymmetric synthesis. [source] Anatase Titanium Dioxide Crystallization by a Hydrolysis Reaction of Titanium Alkoxide without AnnealingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Kunio Funakoshi The crystallization of anatase titanium dioxide (TiO2) was achieved by a hydrolysis reaction of titanium alkoxide without annealing. The hydrolysis reaction rates of tetraethyl orthotitanate were indicated by a function of the concentration of acetylacetone added. The degree of crystallinity of the product particles was influenced by the amounts of acetylacetone and seed crystals. Anatase TiO2 was crystallized by restraining the rapid increase in supersaturation of TiO2 and the consequent nucleation of amorphous TiO2. The degree of crystallinity of the product particles also changed with the types of seed crystals used, and was strongly influenced by the specific surface areas of the seed crystals. [source] Thin Films of ZrO2 for High- k Applications Employing Engineered Alkoxide- and Amide-Based MOCVD Precursors,CHEMICAL VAPOR DEPOSITION, Issue 2-3 2007R. Thomas Abstract Ultrathin ZrO2 films were deposited on SiOx/Si in a multiwafer planetary metal-organic (MO)CVD reactor combined with a liquid delivery system. Two different alkoxide-based precursors, [Zr(OiPr)2(tbaoac)2] and [Zr(OtBu)2(tbaoac)2] are compared with two amide-based precursors, [Zr(NEt2)2(dbml)2] and [Zr(NEtMe)2(guanid)2]. Growth rate, surface roughness, density, and crystallization behavior are compared over a wide range of deposition temperatures (400,700,°C). In addition, the influence of the solvents, n -butylacetate, toluene, and hexane, is discussed. The best growth results in terms of low temperature deposition rate, surface roughness, film density, and carbon content were obtained for the new [Zr(NEtMe)2(guanid)2] precursor. The electrical properties were investigated with metal,insulator,semiconductor (MIS) capacitors. The relative dielectric permittivity was in the range 17,24, depending on the precursor. Compared to standard SiO2 capacitors of similar equivalent oxide thickness, low leakage currents were obtained. [source] The Synthesis of ZrO2/SiO2 Nanocomposites by the Two-Step CVD of a Volatile Halogen-Free Zr Alkoxide in a Fluidized-Bed Reactor,CHEMICAL VAPOR DEPOSITION, Issue 1 2007W. Xia Abstract ZrO2/SiO2 nanocomposites with Zr loadings in the range 0.88 wt,% to 12.2 wt,% were prepared by a two-step metal-organic (MO)CVD process in a fluidized-bed reactor with the Zr alkoxide [Zr(OiPr)2(tbaoac)2] as the precursor. The high surface area of silica was hardly diminished by the deposition, and the deposited zirconia species were highly dispersed, as indicated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) investigations. The XPS data reveal a linear increase of the Zr surface concentration with increasing Zr loading. The high degree of dispersion is attributed to a strong interaction between the zirconia species and the support through the formation of Si-O-Zr bonds. Correspondingly, the intensity of the isolated silanol bands detected by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was found to decrease with increasing Zr loading. [source] ChemInform Abstract: Synthesis of 2-Oxazolines and 2-Thiazolines Using Lanthanide Amino Alkoxide.CHEMINFORM, Issue 8 2008V. Padmavathi 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] One-Pot Synthesis of Metalated Pyridines from Two Acetylenes, a Nitrile, and a Titanium(II) Alkoxide.CHEMINFORM, Issue 42 2005Ryoichi Tanaka No abstract is available for this article. [source] Synthesis of para -Amino Benzoic Acid,TiO2 Hybrid Nanostructures of Controlled Functionality by an Aqueous One-Step ProcessEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 6 2008Raed Rahal Abstract In situ amino acid surface-modified TiO2 nanoparticle syntheses were performed by a simple one-pot hydrolysis of heteroleptic titanium alkoxide [Ti(OiPr)3(O2CC6H4NH2)]m in water with NnBu4Br. This process allowed precise control of the surface grafting rate by varying the amount of precursors and provided highly functionalized nanomaterials. Their compositions and microstructures were determined by C, H and N elemental analyses, TGA-MS, 13C CP-MAS NMR, XRD, TEM, BET, Raleigh diffusion, FTIR, Raman, XPS and UV/Vis experiments. The results indicated that (i) the aggregation rate increased with an increase in the loading of the organic substrate and (ii) the amino acid is chemisorbed as a carboxylate group onto the TiO2 nanoparticles, which leads to a strong interaction between the amino acid and the TiO2 nanoparticle and good stability of these hybrids. Applications of low-aggregated nanomaterials were demonstrated as efficient protection additive against UVA + UVB radiations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Self-Organized Nanocrystalline Organosilicates in Organic-Inorganic Hybrid FilmsADVANCED MATERIALS, Issue 17 2009Masahide Takahashi Organic-inorganic hybrid films containing layered organosilica nanocrystals are obtained by an alcohol-free hydrolytic sol-gel process from a mono-functionalized organically modified alkoxide. Kinetically controlled self-organization is used to design the hybrid nanocomposite films. The layered nanocrystals are shown to be oriented within the films, which exhibited optical anisotropy (,n,>,10,3); the hybrid nanocomposite material is shown to be suitable for microfabrication by soft lithography. [source] A Remarkable Titanium-Catalyzed Asymmetric Strecker Reaction using Hydrogen Cyanide at Room TemperatureADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Balamurugan Ramalingam Abstract Close to perfect enantioselectivity (up to 98% ee) is obtained for the formation of amino nitriles using hydrogen cyanide (HCN) as the cyanide source at room temperature for the first time. In an operationally simple process, the catalyst generated from a partially hydrolyzed titanium alkoxide (PHTA) and (S)- N -salicyl-,-amino alcohol ligand, catalyzes the cyanation of imines in a short reaction time. [source] Enantioselective Silylcyanation of Aldehydes and Ketones by a Titanium Catalyst Prepared from a Partially Hydrolyzed Titanium Alkoxide and a Schiff Base LigandADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Kazuhiko Yoshinaga Abstract In the presence of small amount (0.2,1.0 mol%) of a titanium complex catalyst prepared from a partially hydrolyzed titanium alkoxide and an optically active tridentate Schiff base ligand, the enantioselective silylcyanation of aldehydes and ketones proceeded in a short reaction time at room temperature to afford the corresponding optically active cyanohydrin derivatives in excellent chemical yield with high enantiomeric excess (86,97% ee). The results indicate that partially hydrolyzed titanium alkoxides are a promising titanium source for the preparation of efficient catalysts for asymmetric synthesis. [source] Coimmobilization of malic enzyme and alanine dehydrogenase on organic,inorganic hybrid gel fibers and the production of L -alanine from malic acid using the fibers with coenzyme regenerationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010Koji Nakane Abstract Malic enzyme (EC 1.1.1.39) and alanine dehydrogenase (EC 1.4.1.1) were entrap-immobilized on hybrid gel fibers of cellulose acetate (CA) and zirconium (Zr) alkoxide by air-gap wet spinning. The production of L -alanine from malic acid with coenzyme regeneration was examined with the enzymes immobilized on the fibers. The productivity of L -alanine of the immobilized enzymes decreased to approximately one-fifth of that of free enzymes, but the CA,Zr-fiber-immobilized enzymes retained a high level of productivity after repeated use. Reduced form of nicotinamide adenine dinucleotide (NADH) recycling also occurred effectively for the enzymes immobilized on the fiber. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Synthesis of 13C3 -hydroxyacetoneJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 9 2003Christopher W. Dicus Abstract 13C3 -Hydroxyacetone is prepared in three steps from 13C2 -2-bromoacetic acid. Bromide displacement by sodium p -methoxybenzyl alkoxide followed by treatment of the carboxylic acid with 13C-methyl lithium furnishes PMB-protected hydroxyacetone. Deprotection using DDQ delivers the title compound. Copyright © 2003 John Wiley & Sons, Ltd. [source] Nanocoating hybrid polymer films on large quantities of cohesive nanoparticles by molecular layer depositionAICHE JOURNAL, Issue 4 2009Xinhua Liang Abstract The conformal coating of ultra-thin aluminum alkoxide (alucone) polymer films on primary silica and titania nanoparticles using molecular layer deposition (MLD) in a fluidized bed reactor from 100 to 160 °C is described. In situ mass spectrometry revealed that the growth of alucone MLD films was self-limiting as a function of the individual trimethylaluminum and ethylene glycol exposures. The composition and highly conformal alucone films throughout the surface of both silica and titania nanoparticles were confirmed. The highest growth rate was observed at the lowest sample temperature. Primary nanoparticles were coated individually despite their strong tendency to aggregate during fluidization. Based on the results of chemical and thermogravimetric analysis, the value of x in the formula of Al(OCH2CH2O)x was estimated to be 1.9. The calculated film density slightly increased from 2.0 ± 0.1 to 2.2 ± 0.1 g/cm3 with the increasing of temperature from 100 to 160 °C. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Titanium-mediated living radical styrene polymerizations.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2006Abstract The effects of solvents, additives, ligands, and solvent in situ drying agents as well as catalyst and initiator concentrations have been investigated in the Cp2TiCl-catalyzed radical polymerization of styrene initiated by epoxide radical ring opening. On the basis of the solubilization of Cp2Ti(III)Cl and the polydispersity of the resulting polymer, the solvents rank as follows: dioxane , tetrahydrofuran > diethylene glycol dimethyl ether > methoxybenzene > diphenyl ether , bulk > toluene , pyridine > dimethylformamide > 1-methyl-2-pyrrolidinone > dimethylacetamide > ethylene carbonate, acetonitrile, and trioxane. Alkoxide additives such as aluminum triisopropoxide and titanium(IV) isopropoxide are involved in alkoxide ligand exchange with the epoxide-derived titanium alkoxide and lead to broad molecular weight distributions, whereas similarly to strongly coordinating solvents, ligands such as bipyridyl block the titanium active site and prevent the polymerization. By contrast, softer ligands such as triphenylphosphine improve the polymerization in less polar solvents such as toluene. Although mixed hydrides such as lithium tri- tert -butoxyaluminum hydride, sodium borohydride, and lithium aluminum hydride react with bis(cyclopentadienyl)titanium dichloride to form mixed titanium hydride species ineffective in polymerization control, simple hydrides such as lithium hydride, sodium hydride, and especially calcium hydride are particularly effective as in situ trace water scavengers in this polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2015,2026, 2006 [source] Formation of a living anionic oligomer of ethylphenylketene on polystyrene beads and its application to the solid-supported synthesis of poly(methyl methacrylate)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2002Atsushi Sudo The anionic oligomerization of ethylphenylketene (EPK) by lithium benzyl alkoxide on a polystyrene resin readily afforded the corresponding lithium enolate immobilized on beads through a benzyl ester linker. The lithium enolate so prepared was applied as a solid-supported initiator for the anionic synthesis of poly(methyl methacrylate), which was readily isolated from the resin by selective cleavage of the benzyl ester linker. [source] Anatase Titanium Dioxide Crystallization by a Hydrolysis Reaction of Titanium Alkoxide without AnnealingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006Kunio Funakoshi The crystallization of anatase titanium dioxide (TiO2) was achieved by a hydrolysis reaction of titanium alkoxide without annealing. The hydrolysis reaction rates of tetraethyl orthotitanate were indicated by a function of the concentration of acetylacetone added. The degree of crystallinity of the product particles was influenced by the amounts of acetylacetone and seed crystals. Anatase TiO2 was crystallized by restraining the rapid increase in supersaturation of TiO2 and the consequent nucleation of amorphous TiO2. The degree of crystallinity of the product particles also changed with the types of seed crystals used, and was strongly influenced by the specific surface areas of the seed crystals. [source] Fine Patterning of Hybrid Titania Films by Ultraviolet IrradiationJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2003Hiyoro Segawa Photosensitive hybrid titania films have been prepared from titanium butoxide modified with ,-diketone and methacrylic acid. When this film is exposed to UV light, the ,-diketonato chelate from the alkoxide and ,-diketone is dissociated, and the unsaturated hydrocarbon of methacrylic acid is polymerized. These structural changes in the gel film have led to a difference between the solubility of irradiated and unirradiated parts in the film; therefore, a fine patternable hybrid titania film has been fabricated. [source] Encapsulation and/or Release Behavior of Bovine Serum Albumin within and from Polylactide-Grafted Dextran MicrospheresMACROMOLECULAR BIOSCIENCE, Issue 4 2004Tatsuro Ouchi Abstract Summary: Polylactide (PLA)-grafted dextran (Dex- graft -PLA) of various contents of sugar units was synthesized by anionic polymerization of L -lactide (L -LA) using the alkoxide of partially trimethylsilylated dextran (TMSDex) and subsequently removing the trimethylsilyl (TMS) groups. The copolymer showed different solubility from L -LA homopolymer with increasing the content of sugar units. We prepared bovine serum albumin (BSA)-loaded microspheres (MS)s according to a water-in-oil-in-water emulsion-solvent evaporation/extraction method using methylene chloride/DMSO as an organic cosolvent. MSs prepared from Dex- graft -PLA [MS(Dex- graft -PLA)s] exhibited higher loading efficiency of BSA than MSs prepared from PLLA [MS(PLLA)s]. The in vitro release rate of BSA from MS(Dex- graft -PLA) was faster than that from MS(PLLA). BSA released from MS(Dex- graft -PLA) maintained the secondary structure of native BSA to a great extent, compared with BSA released from MS(PLLA). Confocal fluorescence images of the differential interference micrographs over the fluorescence images of MS(PLLA) and MS(Dex- graft -PLA). [source] Kinetics Approximation Considering Different Reactivities of the Structural Units Formed by the Anionic Copolymerization of 1,3-Butadiene and Styrene Using Al/Li/Ba as InitiatorMACROMOLECULAR REACTION ENGINEERING, Issue 8 2009José. A. Tenorio López Abstract The copolymerization reaction of butadiene and styrene copolymers prepared by anionic living polymerization using an initiator composed of alkyl aluminum, n -butyl lithium, and barium alkoxide is studied using a kinetic model that considers the reactivity of active sites to be different; this assumption is justified by the varying geometric configurations. With the first-order Markov model, the expressions for the fraction of active sites and dyad distribution are obtained. The rate constants are determined by fitting to the conversion and Bernoulli dyad data using the nonlinear least squares method. The conversion and dyad sequence distribution are correctly predicted, and the experimental results indicate that the microstructure and sequence distribution do not change with the conversion and temperature. [source] Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and DienesMACROMOLECULAR SYMPOSIA, Issue 1 2004Alain Deffieux Abstract The influence of MgR2 and AlR3 additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s-Bu2Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4- to 1,2- chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R3Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed. Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators. [source] Microstructure-thermal property relationship of high trans -1,4-poly(butadiene) produced by anionic polymerization of 1,3-butadiene using an initiator composed of alkyl aluminum, n -butyl lithium, and barium alkoxidePOLYMER ENGINEERING & SCIENCE, Issue 1 2009Juan J. Benvenuta-Tapia This article deals with the characterization of high trans -1,4-poly(butadiene) (TPBD) prepared by means of an anionic polymerization using an initiator composed of alkyl aluminum, n -butyl lithium, and barium alkoxide. By controlling both initiator composition and polymerization temperature, a set of TPBD was prepared with well-known number of 1,4-trans units, molecular weight distribution, and average molecular weight. Analyses by differential scanning calorimetry and diffraction of wide-angle X-rays showed a direct relationship between the microstructure of the polymer and its thermal properties. By increasing the number of 1,4-trans units (70,90%), the crystallinity of the polymer was increased (10,30%); polymers with less than 65% of 1,4-trans units were amorphous, whereas TPBD with a number of 1,4-trans units greater than 80% were polymorphous and presented two endothermic transitions. Summing up, the results presented in this article indicate that cyclohexane solutions of alkyl aluminum, n -butyl lithium, and barium alkoxide allow produce polybutadienes with enough amount of 1,4-trans units to display a regular microstructure that makes them susceptible to experience-induced crystallization, likewise at a reaction rate similar to that observed for the commercial production of poly(butadiene) with n -butyl lithium. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers [source] Fast and clean dechlorination of alkyl and aryl (poly)chlorides catalysed by bimetallic Ni,Al clusters in the presence of t -BuOHAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 9 2001Xavier Jurvilliers Abstract The dechlorination of alkyl and aryl (poly)chlorides is rapid and complete upon treatment with a new reduction system consisting of NaH as reagent, Ni,Al clusters as catalyst and t -BuOH as catalytic co-factor. The high efficiency of this combination is presumed to be due to the stabilization of the subnanometre nickel particles formed during reduction by the in-situ -generated alkoxide. Copyright © 2001 John Wiley & Sons, Ltd. [source] Thin Films of ZrO2 for High- k Applications Employing Engineered Alkoxide- and Amide-Based MOCVD Precursors,CHEMICAL VAPOR DEPOSITION, Issue 2-3 2007R. Thomas Abstract Ultrathin ZrO2 films were deposited on SiOx/Si in a multiwafer planetary metal-organic (MO)CVD reactor combined with a liquid delivery system. Two different alkoxide-based precursors, [Zr(OiPr)2(tbaoac)2] and [Zr(OtBu)2(tbaoac)2] are compared with two amide-based precursors, [Zr(NEt2)2(dbml)2] and [Zr(NEtMe)2(guanid)2]. Growth rate, surface roughness, density, and crystallization behavior are compared over a wide range of deposition temperatures (400,700,°C). In addition, the influence of the solvents, n -butylacetate, toluene, and hexane, is discussed. The best growth results in terms of low temperature deposition rate, surface roughness, film density, and carbon content were obtained for the new [Zr(NEtMe)2(guanid)2] precursor. The electrical properties were investigated with metal,insulator,semiconductor (MIS) capacitors. The relative dielectric permittivity was in the range 17,24, depending on the precursor. Compared to standard SiO2 capacitors of similar equivalent oxide thickness, low leakage currents were obtained. [source] The Synthesis of ZrO2/SiO2 Nanocomposites by the Two-Step CVD of a Volatile Halogen-Free Zr Alkoxide in a Fluidized-Bed Reactor,CHEMICAL VAPOR DEPOSITION, Issue 1 2007W. Xia Abstract ZrO2/SiO2 nanocomposites with Zr loadings in the range 0.88 wt,% to 12.2 wt,% were prepared by a two-step metal-organic (MO)CVD process in a fluidized-bed reactor with the Zr alkoxide [Zr(OiPr)2(tbaoac)2] as the precursor. The high surface area of silica was hardly diminished by the deposition, and the deposited zirconia species were highly dispersed, as indicated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) investigations. The XPS data reveal a linear increase of the Zr surface concentration with increasing Zr loading. The high degree of dispersion is attributed to a strong interaction between the zirconia species and the support through the formation of Si-O-Zr bonds. Correspondingly, the intensity of the isolated silanol bands detected by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was found to decrease with increasing Zr loading. [source] Mononuclear Mixed ,-Ketoester-alkoxide Compound of Titanium as a Promising Precursor for Low-Temperature MOCVD of TiO2 Thin Films,CHEMICAL VAPOR DEPOSITION, Issue 6 2003R. Bhakta A monomeric titanium complex suitable for liquid-injection MOCVD applications is synthesized and its molecular structure is determined by single-crystal X-ray diffraction. [Ti(OiPr)2 -(tbaoac)2] (see Figure), (tbaoac),=,tertiarybutylacetoacetonate), is a volatile alkoxide-(beta)diketonate precursor that has a low melting point and very good solubility in common organic solvents. [source] Oxidant-Free Dehydrogenation of Alcohols Heterogeneously Catalyzed by Cooperation of Silver Clusters and Acid,Base Sites on AluminaCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2009Ken-ichi Shimizu Dr. Abstract Trifunctional green catalysis: In-depth characterization shows that oxidant-free selective oxidation of alcohols by silver nanoparticles on ,-Al2O3, as a new heterogeneous catalyst, proceeds through cooperation of silver, acid, and base sites (see figure). A ,-alumina-supported silver cluster catalyst,Ag/Al2O3,has been shown to act as an efficient heterogeneous catalyst for oxidant-free alcohol dehydrogenation to carbonyl compounds at 373,K. The catalyst shows higher activity than conventional heterogeneous catalysts based on platinum group metals (PGMs) and can be recycled. A systematic study on the influence of the particle size and oxidation state of silver species, combined with characterization by Ag,K-edge XAFS (X-ray absorption fine structure) has established that silver clusters of sizes below 1,nm are responsible for the higher specific rate. The reaction mechanism has been investigated by kinetic studies (Hammett correlation, kinetic isotope effect) and by in situ FTIR (kinetic isotope effect for hydride elimination reaction from surface alkoxide species), and the following mechanism is proposed: 1),reaction between the alcohol and a basic OH group on the alumina to yield alkoxide on alumina and an adsorbed water molecule, 2),CH activation of the alkoxide species by the silver cluster to form a silver hydride species and a carbonyl compound, and 3),H2 desorption promoted by an acid site in the alumina. The proposed mechanism provides fundamental reasons for the higher activities of silver clusters on acid,base bifunctional support (Al2O3) than on basic (MgO and CeO2) and acidic to neutral (SiO2) ones. This example demonstrates that catalysts analogous to those based on of platinum group metals can be designed with use of a less expensive d10 element,silver,through optimization of metal particle size and the acid,base natures of inorganic supports. [source] Hydrocarbon-Soluble Calcium Hydride: A "Worker-Bee" in Calcium ChemistryCHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2007Jan Spielmann Abstract The reactivity of the hydrocarbon-soluble calcium hydride complex [{CaH(dipp-nacnac)(thf)}2] (1; dipp-nacnac=CH{(CMe)(2,6- iPr2C6H3N)}2) with a large variety of substrates has been investigated. Addition of 1 to CO and CN functionalities gave easy access to calcium alkoxide and amide complexes. Similarly, reduction of the CN bond in a cyanide or an isocyanide resulted in the first calcium aldimide complexes [Ca{NC(H)R}(dipp-nacnac)] and [Ca{C(H)NR}(dipp-nacnac)], respectively. Complexation of 1 with borane or alane Lewis acids gave the borates and alanates as contact ion pairs. In reaction with epoxides, nucleophilic ring-opening is observed as the major reaction. The high reactivity of hydrocarbon-soluble 1 with most functional groups contrasts strongly with that of insoluble CaH2, which is essentially inert and is used as a common drying agent. Crystal structures of the following products are presented: [{Ca{OC(H)Ph2}(dipp-nacnac)}2], [{Ca{NC(H)Ph}(dipp-nacnac)}2], [{Ca{C(H)NC(Me)2CH2C(Me)3}(dipp-nacnac)}2], [{Ca{C(H)NCy}(dipp-nacnac)}2], [Ca(dipp-nacnac)(thf)]+[H2BC8H14], and [{Ca(OCy)(dipp-nacnac)}2]. The generally smooth and clean conversions of 1 with a variety of substrates and the stability of most intermediates against ligand exchange make 1 a valuable key precursor in the syntheses of a wide variety of ,-diketiminate calcium complexes. [source] A Family of 1,1,3,3-Tetraalkylguanidine (H-TAG) Solvated Zinc Aryloxide Precatalysts for the Ring-Opening Polymerization of rac -LactideEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2010Julia J. Ng Abstract Reaction of [Zn(,-TAG){N(SiMe3)2}]2 {TAG = N=C[N(CH2CH3)2N(CH3)2] (DEDMG), N=C{[NCH2CH2CH2CdH2(N,Cd)]N(CH2CH3)2} (DEPYRG) and N=C{[NCH2CH2CH2CH2CeH2(N,Ce)]N(CH2CH3)2} (DEPIPG)} with 2 equiv. of ethanol (EtOH) and 2 equiv. of HOAr {OAr = OC6H3(CMe3)-2-(CH3)-6 (BMP) or OC6H2[C(CH3)3]2 -2,6-(CH3)-4 (4MeDBP)} results in dizinc alkoxides with the general formula [Zn(,-OEt)(OAr)(H-TAG)]2 (1,3). Et2Zn was additionally treated with 2 equiv. of 1,1,3,3-tetramethylguanidine (H-TMG) and H-BMP or HOC6H3(C6H5)2 -2,6 to yield [Zn(BMP)2(H-TMG)2] (4) and [Zn{OC6H3(C6H5)2 -2,6}2(H-TMG)2] (5). Complexes 1, 2, 4, and 5 were characterized by single-crystal X-ray diffraction. Polymerization of rac -lactide with 1,5 and [Zn(,-OMe)(4MeDBP)(H-TMG)]2 (6) were found to generate polylactide (PLA). The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, FTIR spectroscopy, and 1H and 13C NMR spectroscopic studies. [source] Syntheses of O6 -Alkyl- and Arylguanine Derivatives: Nucleobase Adducts Derived from Styrene 7,8- and 3,4-OxidesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2006Jan Novák Abstract A series of O6 -alkyl and -arylguanine derivatives that may be formed in vivo after exposure to styrene has been prepared by reaction of 6-(4-aza-1-azoniabicyclo[2.2.2]octyl)-purine with alkoxides and aryloxides, respectively. Themonoprotected diols 2-allyloxy- or 2-benzyloxy-1-phenylethanol and 2-allyloxy- or 2-benzyloxy-2-phenylethanol were used as synthetic equivalents of styrene 7,8-oxide. 4-Vinylphenol, 2-(4-hydroxyphenyl)ethanol and 4-hydroxyphenylacetic acid were used as synthetic equivalents of arene oxide metabolites of styrene, i.,e., styrene 3,4-oxide, 4-(2-hydroxyethyl)benzene 1,2-oxide and 4-carboxymethylbenzene 1,2-oxide, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis and Molecular Structure of New Unsaturated Analogues of Nucleotides Containing Six-Membered RingsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2005Valery K. Brel Abstract The reaction of 1-(chloromethyl)-3-(diethoxyphosphonyl)allenes 15 and 16 with purine and pyrimidine bases in the presence of cesium carbonate afforded new acyclic analogs of nucleotides containing a 1,2-alkadienic skeleton (17,24). Intramolecular cyclization of the alkoxides tethered to the allenyl moiety yielded dihydropyrans 33,38 and dihydrofurans 39 and 40. Dealkylation of the dihydropyrans led to the corresponding phosphonic acids. The molecular structures of new nucleotide analogs 33 and 36 were determined by single-crystal X-ray analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] | |||||||||||||||||||||||||