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TiCl4
Selected AbstractsStructure,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] Reaction of 1,3,5-Triazacyclohexanes with TiCl4: Formation of Cationic ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2005Randolf D. Köhn Abstract N -substituted 1,3,5-triazacyclohexanes [R3TAC; R = cyclohexyl, p -fluorobenzyl or Ph(CH2)n (n = 1, 2, 3)] react with excess TiCl4 to give the corresponding cationic ,3 complexes [(R3TAC)TiCl3][Ti2Cl9]. Attempts to prepare complexes with titanium-free anions at lower Ti:R3TAC ratio or with added Me3SiOTf lead to the same cations with [Ti2Cl10]2, and [Ti2Cl8(OTf)], anions. Five complexes as well as (p -fluorobenzyl)3TAC have been characterised by X-ray crystallography. The ring C,H bonds engage in hydrogen bonding interactions in the crystals and strongly solvent and anion dependent 1H NMR signals are detected in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Preparation of Optically Active ,-Amino[3]ferrocenophanes , Building Blocks for Chelate Ligands in Asymmetric CatalysisEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2003Patrick Liptau Treatment of 1,1,-diacetylferrocene (4) with dimethylamine and TiCl4 yielded the unsaturated dimethylamino-substituted [3]ferrocenophane product 5. Its catalytic hydrogenation gave the corresponding saturated [3]ferrocenophane system 6 (trans/cis , 7:1). The rac -[3]ferrocenophane amine 6 was partially resolved (to ca. 80% ee) by means of L - or D - O,O, -dibenzoyltartrate salt formation. Treatment of 4 with the pure (R)- or (S)-methyl(1-phenylethyl)amine (8)/TiCl4 gave the corresponding optically active unsaturated [3]ferrocenophane amines (R)-(+)- 9 and (S)-(,)- 9, respectively. Their catalytic hydrogenation again proceeded trans -selectively, giving the corresponding saturated diastereomeric [3]ferrocenophane amines (1R,3R,5R)- 10a and (1S,3S,5R)- 10b [starting from (R)- 9], their enantiomers ent - 10a and ent - 10b were obtained from (S)- 9, but with a poor asymmetric induction (10a/10b < 2:1). Quaternization of 6 (CH3I) followed by amine exchange using (R)- or (S)-methyl(1-phenylethyl)amine (8), respectively, proceeded with overall retention. Subsequent chromatographic separation gave the pure diastereoisomers (1R,3R,5R)- 10a and (1S,3S,5R)- 10b [from (R)- 8, ent - 10a and ent - 10b from (S)- 8] in > 60% yield. Subsequently, the benzylic (1-phenylethyl) auxiliary was removed from the nitrogen atom by catalytic hydrogenolysis to yield the enantiomerically pure (> 98%) ([3]ferrocenophanyl)methylamines (1R,3R)- 11 and (1S,3S)- 11, respectively, which were converted into the corresponding dimethylamino-substituted [3]ferrocenophanes (1R,3R)- 6 and (1S,3S)- 6. Each enantiomer from the following enantiomeric pairs was isolated in its pure form and characterized by X-ray diffraction: (R)- 9/(S)- 9; (1R,3R,5R)- 10a/(1S,3S,5S)- 10a; (1R,3R,5S)- 10b/(1S,3S,5R)- 10b; (1R,3R)- 11/(1S,3S)- 11. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] (4-Acyl-5-pyrazolonato)titanium Derivatives: Oligomerization, Hydrolysis, Voltammetry, and DFT StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2003Francesco Caruso Abstract Twenty 4-acyl-5-pyrazolonato (Q) titanium derivatives of varied nuclearity have been synthesized from Ti(OR)4 or TiCl4 and characterized with spectroscopic methods (IR, NMR, ESI-MS). While Ti,(,-diketonato) cleavage is not seen in isolated solids, Ti,O(alkoxy) (or Ti,Cl) bonds cleave upon hydrolysis, leading to several structural forms, including oligomers. Ionic Q species with no Ti, i.e., obtained after Ti,Q cleavage, are seen for some Ti,Q derivatives by ESI-MS, which also indicates a varied nuclearity for a given species, e.g., the isolated polynuclear [Q2Ti-,-O]n has several "n" values. Mononuclear Ti complexes are obtained under rigorous anhydrous conditions. The cis structures of the mononuclear species (QT)2Ti(OCH3)2, QT = 3-methyl-4-(neopentylcarbonyl)-1-phenylpyrazol-5-onato have been analyzed with DFT methods. A trans influence is a major driving force that accounts for several sets of Ti,O bonds. One of the cis stereoisomers is 56 kcal/mol higher in energy than the other two. In contrast, all (QT)2TiCl2cis isomers show similar energies. Voltammetry of the mononuclear species (QT)2Ti(OnPr)2 and the antitumor tetranuclear compound [(QB)2Ti-,-O]4, (QB = 4-benzoyl-3-methyl-1-phenylpyrazol-5-onato) indicate that the TiIV is less prone to reduction to TiIII in the latter (Epc for the TiIV/TiIII couple is ,1.71 V and ,1.46 V versus Fc+/Fc, respectively). Potential antitumor compounds having a Ti/Q ratio of 1:1 do not disproportionate, unlike the equivalent acetylacetonato derivatives, and are water-soluble. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Lewis Acid Mediated Aminobenzannulation Reactions of ,-Ketoalkynes: Synthesis of 1-Aminocarbazoles and 9-Aminopyrido[1,2- a]indolesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2009Diego Facoetti Abstract 2-Acyl- N -propargylindoles 1 and 2-acyl-3-propargylindoles 5 undergo aminobenzannulation reactions with pyrrolidine in the presence of an appropriate Lewis acid to give 9-aminopyrido[1,2- a]indoles 6 and 1-aminocarbazoles 7, respectively. The selection of the appropriate Lewis acid, TiCl4 or GaCl3 for 1 and InCl3 for 5, allows the domino process involving the initial formation of an enamine intermediate, followed by a regioselective 6- exo - dig intramolecular nucleophilic attack of the nucleophilic terminus of the unsaturated system (the ,-carbon of the enamino moiety) to the carbon,carbon triple bond. Moreover, several features concerning the reaction mechanism and the role of both catalysts, in connection with the electronic properties of the reacting alkynes, are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Asymmetric Homoaldol Reactions with Cyclohex-2-enyl N,N -Diisopropylcarbamate: Kinetic Resolution, Elucidation of the Stereochemical Course and Applications in the Synthesis of Hexahydroisobenzofuran-4-(1H)-onesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2007Jochen Becker Abstract Enantio-enriched cyclohex-2-enyl N,N -diisopropylcarbamate (5) is stereospecifically deprotonated by sec -butyllithium/(,)-sparteine (9) to form the configurationally stable lithium complex 7·9. A kinetic resolution of rac - 5 by n -butyllithium/(,)-sparteine (9) yielded (R)- 5 with up to 99,% ee. Electrophilic substitution with tin electrophiles proceeds in a anti -SE, fashion as shown by chemical correlations. The synthesized allylstannanes 10 undergo a highly stereospecific TiCl4 -mediated homoaldol reaction with various aldehydes, yielding syn -configured homoaldol products 12. These were transferred into all - cis -configured hexahydroisobenzofuran-4(1H)-ones 22 by BF3·OEt2 -mediated reactions with aldehydes. The configurations of several products were determined by X-ray structure analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Highly Diastereoselective [3+2] Cyclopenta[b]annulation of Indoles with2-Arylcyclopropyl Ketones and Diesters,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2006Chelvam Venkatesh Abstract A highly diastereoselective Lewis acid (BF3·Et2O or TiCl4) induced [3+2] cycloaddition of substituted and unsubstituted indoles with 2-arylcyclopropyl ketones/diesters yielding cyclopenta[b]indoles in high yields is reported. This methodology has also been extended to tetrahydrocarbazole, cyclopenta[b]- and cyclohepta[b]indoles affording tetracyclic propellane type frameworks in modest yields. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The Synthesis and Reactivity of Group 4 Zwitterionic Complexes of the Type Mt+CH2AlCl3,: One-Component Stereoselective Polymerization and Oligomerization Catalysts for Olefins and AcetylenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2004John J. Eisch Abstract A reinvestigation of the interaction of TiCl4 with 2 equiv. of Me3Al in toluene between ,78 °C and 25 °C over 24 h has now established that the ultimate black product obtained is an associated zwitterion of the type [Ti+,CH2,AlCl3,]n, supported by multinuclear NMR spectroscopy and mass spectrometric and gasometric analyses of the gases evolved (CH4, H2) upon its protolysis. Chemical reactions of the zwitterion have corroborated specific aspects of its proposed structure: 1) its methylene character, by its transformation of benzophenone into 1,1-diphenylethylene; 2) its divalent titanium content, by the substantial reductive dimerization of benzophenone to tetraphenylethylene, and 3) its Lewis acidic Ti center, by its catalytic isomerization of trans -stilbene oxide to 1,1-diphenylacetaldehyde. Similar individual reactions of ZrCl4 or HfCl4 with Me3Al have led to the analogous zwitterions [Zr+,CH2,AlCl3,]n and [Hf+,CH2,AlCl3,]n, respectively. These zwitterions of Ti, Zr and Hf have been proven to be capable of the cyclotrimerization and/or polymerization of acetylenes with varying facility, as evidenced by their catalytic action on 1-hexyne, phenylacetylene, di- n -butylacetylene, and diphenylacetylene. Furthermore, all three zwitterions were able to polymerize ethylene, without any added cocatalyst, with an activity following the order Zr > Ti > Hf. The Ti and Zr zwitterions effected the stereoselective polymerization of propylene to yield 50% of isotactic polymer, and all three catalysts induced the polymerization of 1-hexene to yield 85% (Zr, Hf) or 100% (Ti) of isotactic polymer. These oligomerizations and stereoselective polymerizations of acetylenes and olefins can be rationalized through a model for the active site resembling a three-membered metallacyclopropa(e)nium ion intermediate formed from the attack of the Group 4 metal zwitterion on the unsaturated hydrocarbon. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Toward Diels,Alder Reactions on a Solid Support Using Polymer Bound N -Substituted 3-Hydroxy-4,4-dimethyl-2-pyrrolidinone Acrylate DerivativesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2004Rhalid Akkari Abstract Several N -substituted 3-hydroxy-4,4-dimethyl-2-pyrrolidinone acrylate derivatives, selected to allow their attachment to a polymer, have been prepared and tested as dienophiles in the Diels,Alder reaction. The experiments, performed under TiCl4 catalysis in solution or the solid phase with isoprene and cyclopentadiene as dienes, pointed out the difficulties associated with some of these compounds that failed to give the corresponding cycloadduct. 13C NMR studies provided some evidence regarding the nature of the interactions between the acrylate compounds and TiCl4. It appears that the outcome of the reaction is dependent on the acrylate structure and that the 4-(3-hydroxy-4,4-dimethyl-2-oxopyrrolidin-1-yl)benzoic acid acrylate derivatives are highly efficient to give the cycloadduct in good yield and with high regio- or endoselectivity in both solution and solid-phase reaction conditions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] A Delivery System for Self-Healing Inorganic Films,ADVANCED FUNCTIONAL MATERIALS, Issue 22 2008Harvey A. Liu Abstract Multilayer composites that utilize polymeric and brittle inorganic films are essential components for extending the lifetimes and exploiting the flexibility of many electronic devices. However, crack formation within the brittle inorganic layers that arise from defects as well as the flexing of these multilayer composite materials allows the influx of atmospheric water, a major source of device degradation. Thus, a composite material that can initiate self-healing upon the influx of environmental water through defects or stress-induced cracks would find potential applications in multilayer composite materials for permeation barriers. In the present study, the reactive metal oxide precursor TiCl4 is encapsulated within the pores of a degradable polymer, poly(lactic acid) (PLA). Electrospun PLA fibers are found to be reactive to atmospheric water leading to the hydrolysis of the degradable polymer shell and subsequent release of the reactive metal oxide precursor. Release of the reactive TiCl4 from the pores results in hydrolysis of the metal oxide precursor, forming solid titanium oxides at the surface of the fibers. The efficacy of this self-healing delivery system is also demonstrated by the integration of these reactive fibers in the polymer planarization layer, poly(methyl methacrylate), of a multilayer film, upon which an alumina barrier layer is deposited. The introduction of nanocracks in the alumina barrier layer lead to the release of the metal oxide precursor from the pores of the fibers and the formation of titanium dioxide nanoparticles within the crack and upon the thin film surface. In this study the first delivery system that may find utility for the self-healing of multilayer barrier films through the site-specific delivery of metal oxide nanoparticles through smart reactive composite fibers is established. [source] Photocatalytic Selective Oxidation of 4-Methoxybenzyl Alcohol to Aldehyde in Aqueous Suspension of Home-Prepared Titanium Dioxide CatalystADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2007Giovanni Palmisano Abstract The photocatalytic oxidation of 4-methoxybenzyl alcohol to p -anisaldehyde (PAA) was performed in water with organic-free suspensions of home-prepared and commercial titanium dioxide (TiO2) catalysts. The nanostructured TiO2 samples were synthesised by boiling aqueous solutions of titanium tetrachloride (TiCl4), under mild conditions, for different times. The crystallinity increased with the boiling time. The 4-methoxybenzyl alcohol oxidation rate followed the same pattern but the highest yield (41.5,% mol) to PAA was found for the least crystalline sample, that showed a quantum efficiency of 0.116,%. A comparison with two commercial TiO2 samples showed that all the home-prepared catalysts exhibited a PAA yield higher than that of commercial ones. The only by-products present were traces of 4-methoxybenzoic acid and aliphatic products, carbon dioxide being the other main oxidation product. [source] One-pot synthesis of 2H -thiochromenes via TiCl4 -promoted reaction of 2- tert -butylthiobenzaldehydes with activated alkenesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2009Chang Hoon Lee A facile synthesis of 2H -thiochromenes through TiCl4 -promoted reaction of 2- tert -butylthiobenzaldehydes with activated alkenes is described. J. Heterocyclic Chem., (2009). [source] Synthesis of heterocycles from molecular nitrogen as a nitrogen sourceJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2000Miwako Mori Nitrogen fixation is a very attractive process. We succeeded in nitrogen fixation using a TiCl4 - or Ti(O- i -Pr)4 -Li-TMSCl system. Nitrogen fixation proceeds at room temperature under 1 atmosphere pressure of nitrogen to give a mixture of titanium nitride complex 12, titanium nitrogen complex 13, and N(TMS)4. Using the titanium nitrogen complexes 1, various heterocycles were synthesized from the corresponding ketocarbonyl compounds. Nitrogen in air could be fixed using this method. The total syntheses of lycopodine and monomolin I were achieved from nitrogen in air as the nitrogen source. On the other hand, transmetalation of the nitrogen moiety of titanium nitrogen complexes 1 to a palladium complex was realized, and the non-substituted anilines could be synthesized from ArX and N2 in the presence of the palladium catalyst. Furthermore, amide could be synthesized from ArX, CO, and N2 using the palladium catalyst. [source] Carbon-14 radiosynthesis of combretastatin A-1 (CA1) and its corresponding phosphate prodrug (CA1P)JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 14 2009Rodney T. Brown Abstract The natural product combretastatin A-1 (CA1) is isolated from the African bush willow tree, a member of the Combretaceae family. CA1 has important medicinal value, due in part to its ability to inhibit tubulin assembly. The prodrug combretastatin A-1 diphosphate (CA1P; OXi4503) is currently in human Phase I clinical trials as a vascular disrupting agent. This paper describes the carbon-14 radiosynthesis of [4,- 14C]CA1 and the corresponding phosphate prodrug salt [4,- 14C]CA1P in high specific activity (55,mCi/mmol). The carbon-14 label was introduced by methylation of the C-4, protected phenolic moiety of the CA1 precursor following removal of the tert -butyldimethylsilyl protecting group in the presence of [14C]methyl iodide. This was accomplished in excellent yield without significant Z to E isomerization. The [14C]-precursor ((Z)-1-[3,,[4,- 14C],5,-trimethoxyphenyl]-2-[2,,3,-di-[(isopropyl)oxy]-4,-methoxyphenyl] ethene) was subjected to a de- isopropylation reaction with TiCl4. The tetrabenzyl phosphate derivative of the resulting diol was prepared using fresh dibenzyl phosphite. Debenzylation with trimethylsilylbromide, followed by hydrolysis of the trimethylsilyl ester and adjustment of the pH with dilute aqueous hydrochloric acid yielded [4,- 14C]CA1P with an overall radiochemical yield of 8.4%. Copyright © 2009 John Wiley & Sons, Ltd. [source] Michael Polanyi and the discovery of co-catalysis: Discussion of an autobiographical letter from Michael Polanyi, FRS to Peter H. Plesch of 17 December 1963JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2004P. H. Plesch Abstract The origin of this memoir was a letter from Michael Polanyi (M. P.) to the present writer (P. H. P.) about their researches in the mid-1940s into the mechanism of what are now called cationic polymerizations, at the University of Manchester (England). M. P. analyzes his tactics and the mistakes made in directing this research. When the Manchester-trained researchers made little progress with what was a very recalcitrant problem, M. P. thinking that scientists from a different background might be more sucessful, got P. H. P., from Cambridge, to work with an Oxford-trained chemist. They recognized that the likely cause of the irreproducibility of these polymerizations was the apparatus used which permitted access of atmospheric moisture to the reaction mixtures containing the moisture-sensitive catalytic metal halides. Because the only method for following the very fast polymerizations was by monitoring the accompanying temperature rise, and the reactions had to be done below ambient temperature, the reaction vessel needed to be adiabatic, that is a Dewar (Thermos) flask; hence the problem of how to cool its contents. The solution was P. H. P.'s invention of the pseudo-Dewar vessel, the Dewar space of which, instead of being evacuated permanently, could be filled with air or evacuated. This device permitted the reaction mixture to be made up and cooled, and the reactions to be started without contact with the atmosphere. Thus it was found that isobutene polymerizations, which had stopped unaccountably, could be restarted by water vapor. P. H. P. termed water a "co-catalyst". The consequent "Manchester" theory recognized the monohydrate of TiCl4 as a protonic acid and saw the initiation as due to the protonation of the monomer, with the formation of a tert -carbenium ion, and these ions, formed repetitively, became the propagating species. The Manchester theory was rapidly accepted because it could also explain observations on other related reactions. The involvement of ions established a link with non-aqueous electrochemistry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1537,1546, 2004 [source] Hydrothermal Synthesis of Tetragonal Barium Titanate from Barium Chloride and Titanium Tetrachloride under Moderate ConditionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2002Huarui Xu Tetragonal BaTiO3powders were prepared hydrothermally at 240°C, in only 12 h, using BaCl2·2H2O and TiCl4, which are rather easy to manipulate. Characterization via X-ray diffractometry, scanning electron microscopy, Brunauer,Emmett,Teller analysis, and differential scanning calorimetry confirmed that increasing the NaOH excess concentration (from 0.5M to 2.0M) and decreasing the initial TiCl4concentration (from 0.625M to 0.15M) promotes the formation of tetragonal BaTiO3powders. After reaction, the powders were proved to be phase-pure BaTiO3, with no impurities, such as Cl, and CO32,. [source] Simple Synthesis of Submicrometer Lead Titanate Powder by Precipitation of TiO2 Precursor on PbO ParticulatesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2000Kyoung R. Han A simple way to prepare phase-pure, submicrometer PbTiO3 powder was tried by precipitation. Precipitation was carried out in an aqueous PbO slurry using aqueous TiCl4 and dilute NH4OH at pH 9.5 ± 0.1. The TG/DSC curves of the PT precursor show weight loss of ,7% and two exotherms at 492° and 522°C. They are attributed to the crystallization of tetragonal PbTiO3. XRD shows that tetragonal PbTiO3 can be obtained by heat treatment around 500°C via a noncrystalline state. SEM shows that the PbTiO3 powder calcined at 600°C for 1 h is well crystallized and in the range of 100,300 nm. [source] Effects of MgCl2 Crystallographic Structure on Active Centre Formation in Immobilized Single-Centre and Ziegler,Natta Catalysts for Ethylene PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 21 2008Rubin Huang Abstract The ability of a MgCl2 support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu2 with HCl gave high activity with TiCl4 but low activity with (n -PrCp)2ZrCl2. High polymerization activities with the zirconocene were only obtained with supports of type MgCl2/AlRn(OEt)3,n prepared from the reaction of AlR3 with MgCl2,·,1.1EtOH. These supports are characterized by additional peaks in the X-ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species. [source] Reductive Formation of Isospecific Ti Dinuclear Species on a MgCl2 (110) Surface in Heterogeneous Ziegler-Natta CatalystsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 17 2008Toshiaki Taniike Abstract Dinucleation of TiCl4 on the MgCl2 (100) surface has been conventionally believed as the origin of the stereospecificity of heterogeneous Ziegler-Natta catalysts for propylene polymerization, while the MgCl2 (110) surface has been regarded as non-stereoselective in the absence of organic donors. Based on periodic density functional calculations, we propose a new isospecific Ti dinuclear species on the MgCl2 (110) surface, which is formed as a result of reduction of Ti from 4+ to 3+. The new species closely resembles the dinuclear species on the (100) surface, but two Ti ions are obliquely stacked along the (110) surface through Cl bridges. The results address the importance of the reduction and re-distribution of surface Ti species after contacting with cocatalysts in considering the origin of the stereospecificity. [source] Carbocationic Polymerizations for Profit and FunMACROMOLECULAR SYMPOSIA, Issue 1 2004Ralf M. Peetz Abstract This presentation consists of two largely independent parts: The first åfor Profit, part concerns a bird's eye view of recently commercialized carbocationic processes and materials created by these processes in the author's laboratories whose marketing started during the past ,5 years by various companies. These materials/processes include liquid telechelic polyisobutylene (PIB) for architectural sealants, poly(styrene- b -isobutylene- b -styrene) (PSt- b -PIB- b -PSt) triblocks for thermoplastic elastomers, PIB/PSt-based blocks for coating of medical devices, and PIB-based microemulsions for surface protection of painted metal surfaces. It is concluded that in order to enhance and solidify research in polymer synthesis it would behoove the scientific community to pay increased attention to intellectual property protection. Appropriately managed patenting and publishing activities are self-reinforcing and may be quite profitable. The second "for Fun" part concerns a brief review of the design, synthesis and characterization of two novel fully aliphatic star-block copolymers: ,(PIB- b -PNBD)3 and ,(PNBD- b -PIB)3 (where PNBD = polynorbornadiene). The constituent moieties of these star-blocks are identical except their block sequences are reversed. Motivation for the synthesis of ,(PIB- b -PNBD)3, consisting of a low Tg (,-73°C) PIB inner-corona attached to a high Tg (,320°C) PNBD outer corona, was the expectation that this star-block would exhibit thermoplastic elastomer characteristics, and that it could be used in applications where similar polyaromatic-based TPEs cannot be employed (e.g., magnetic signal storage). The other star-block, ,(PNBD- b -PIB)3, comprises the same building blocks with the PIB and PNBD sequences reversed. We found that the secondary chlorine at the PNBD chain end, in conjunction with TiCl4, is able to initiate the polymerization of isobutylene. Details of the carbocationic polymerization of NBD, together with the microstructure of PNBD, will be discussed. [source] Atmospheric Cold Plasmas for Synthesizing Nanocrystalline Anatase TiO2 using Dielectric Barrier DischargesPLASMA PROCESSES AND POLYMERS, Issue 5 2007Long-Hui Nie Abstract Nanocrystalline anatase TiO2 has been successfully synthesized using TiCl4 and O2 as precursors by atmospheric cold plasmas generated by dielectric barrier discharges (DBD) without extra heating or thermal treatment. For the TiO2 powders synthesized by DBD plasma at an energy density of 5.9 kJ,·,L,1, XRD and TEM analyses revealed that the nanocrystallite size is about 10,15 nm. Only a single crystalline structure of anatase was observed performing XRD, HRTEM and SAED measurements. It was found that the particle size decreased with increasing the discharge power, and that the chlorine contamination dramatically decreased when using high discharge power levels. [source] In situ polymerization of polyethylene/clay nanocomposites using a novel clay-supported Ziegler-Natta catalystPOLYMER COMPOSITES, Issue 10 2009Ahmad Ramazani S.A. Polyethylene/clay nanocomposites (PECNC) were synthesized via in situ Ziegler-Natta catalyst polymerization. Activated catalyst for polymerization of ethylene monomer has been prepared at first by supporting of the cocatalyst on the montmorillonite (MMT) smectite type clay and then active complex for polymerization formed by reaction of TiCl4 and aluminum oxide compound on the clay. Acid wash treatment has been used for increasing hydroxyl group and porosity of the clay and subsequently activity of the catalyst. The nanostructure of composites was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Obtained results show that silica layers of the mineral clay in these polyethylene/nanocomposites were exfoliated, intercalated, and uniformly dispersed in the polyethylene matrix even at very high concentration of the clay. Thermogravimetric analysis (TGA) shows good thermal stability of the PECNCs. Differential scanning calorimeter (DSC) results reveal considerable decrease in the crystalline phase of the PECNC samples. Results of permeability analysis show an increase in barrier properties of PECNC films. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers [source] Polyethylene-Palygorskite nanocomposite prepared via in situ coordinated polymerizationPOLYMER COMPOSITES, Issue 4 2002Junfeng Rong A polyethylene/palygorskite nano-composite (IPC composite) was prepared via an in-situ coordinated polymerization method, using TiCl4 supported on palygorskite fibers as catalyst and alkyl aluminum as co-catalyst. These composites were compared with those prepared by melt blending (MBC composites). It was found that in the IPC composites, nano-size fibers of palygorskite were uniformly dispersed in the polyethylene matrix. In contrast, in the MBC composites, the palygorskite was dispersed as large clusters of fibers. Regarding the mechanical properties of the IPCs, the tensile modulus increased and the elongation at break decreased with increasing fiber content, while the tensile strength passed through a maximum. The tensile strength and elongation at break were much smaller for the MBC composites. The final degree of crystallinity of the IPC composites decreased with increasing palygorskite content. Regarding the kinetics of crystallization, the ratio between the degree of crystallinity at a given time and the final one was a universal function of time. It was found that large amouns of gel were present in the IPC composites and much smaller amountes in the MBC composites. [source] Biomacromolecular engineering: design, synthesis and characterization.POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9-10 2006One-pot synthesis of block copolymers of arborescent polyisobutylene, polystyrene Abstract Novel arborescent block copolymers comprising of an arborescent rubbery polyisobutylene (PIB) midsegment and glassy polystyrene (PSt) end blocks were prepared by sequential addition of monomers. Synthesis was conducted by the use of 4-(2-methoxyisopropyl) styrene as an inimer-type initiator in conjunction with titanium tetrachloride (TiCl4) in 60:40 (v/v) methylcyclohexane/methyl chloride solvent mixture. Isobutylene was polymerized for 1,2,hr and then prechilled styrene in the same solvent mixture was sequentially added with select additives to the reaction flask. The recovered block copolymers were purified and then characterized by 1H-NMR, size exclusion chromatograph (SEC), tensile test, atomic force Microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Samples with 16.4,32.8,wt% PSt and Mn,=,47,600,125,900,g/mol (Mw/Mn,=,2.02,4.45) displayed thermoplastic elastomeric properties with 5,9.2,MPa tensile strength and 490,920% elongation. The arborescent block copolymers showed surface morphologies ranging from spherical to cylindrical/lamellar nanometer-sized discreet PSt phases dispersed in a continuous PIB matrix, with a 10,nm PIB layer on the surface. Drug release profiles of paclitaxel from two arborescent blocks were found to be similar to that measured from Translute®. Copyright © 2006 John Wiley & Sons, Ltd. [source] 2-(Diphenylphosphinoylmethyl)pyrrole,2-(diphenylphosphinomethyl)pyrrole (0.43/0.57) and tetrachlorido(5-diphenylphosphinomethyl-2H -pyrrole-,2N,P)titanium(IV)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010Lewis M. Broomfield The title phosphine oxide,phosphine, 0.43C17H16NOP·0.57C17H16NP, (I)/(II), was obtained as a 0.861,(6):1.139,(6) cocrystallized mixture. Hydrogen bonding between the two constituents leads to the formation of 2:2 solid-state assemblies. Instead of forming the expected simple N,P -chelated system via loss of the N-bound H atom, reaction of 2-(diphenylphosphinomethyl)pyrrole, (II), with TiCl4 leads to the formation of the title titanium(IV) complex, [TiCl4(C17H16NP)], (IV), containing a rearranged neutral ligand in which the N-bound H atom moves to one of the pyrrole C atoms, giving a partially unsaturated ring. [source] Growth and Properties of TiCl4 -Derived CVD Titanium Oxide Films at Different CO2/H2 Inputs,CHEMICAL VAPOR DEPOSITION, Issue 5 2003D.-H. Kuo Abstract Crystalline titanium oxide films with a thickness of 0.09,0.55,,m were prepared at temperatures below 500,°C by CVD using a mixture of titanium tetrachloride (TiCl4), carbon dioxide (CO2), and hydrogen (H2) as reactants. Film thickness decreased with increasing substrate temperature and CO2/H2 input. Nanosized microstructure was obtained at high CO2/H2 input due to the growth retardation of reacted HO-TiCl3* by the unreacted TiCl4 and CO2. That film composition, i.e., the O/Ti ratio, increased with temperature and the CO2/H2 input can be explained by growth kinetics. Unlike film thickness, internal film stress increased with increasing substrate temperature. Adhesion was controlled by compressive internal stress due to the weak bonding between film and substrate. Two growth mechanisms are proposed to explain the tensile and compressive stress states in films produced by CVD. The adsorption-controlled reaction has a film in compressive stress that increases with an increase in temperature. On the other hand, thermally activated CVD produces a film in tensile stress that decreases with an increase in substrate temperature. [source] ChemInform Abstract: A Novel Construction of 2-Benzazepine Scaffold Based on TiCl4 -Mediated Tandem Mannich Reaction , Aromatic Electrophilic Substitution.CHEMINFORM, Issue 18 2010Liangxi Li 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] Pinacol Coupling of Aromatic Aldehydes and Ketones Mediated by TiCl4,Zn in Ethyl Acetate under Ultrasound.CHEMINFORM, Issue 50 2007Ji-Tai Li 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, please click on HTML or PDF. [source] Efficient Method for the Deprotection of tert-Butyldimethylsilyl Ethers with TiCl4,Lewis Base Complexes: Application to the Synthesis of 1,-Methylcarbapenems.CHEMINFORM, Issue 49 2006Akira Iida 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, please click on HTML or PDF. [source] One-Pot Synthesis of Substituted Indole N-Oxides: TiCl4 -Mediated Baylis,Hillman Reaction of ,-Oxo Cyclic Ketene-S,S-acetal with o-Nitrobenzaldehydes and Subsequent Intramolecular Cyclization.CHEMINFORM, Issue 36 2006Wei Pan 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, please click on HTML or PDF. [source] | |||||||||||||||||||||||||