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Zirconium
Terms modified by Zirconium Selected AbstractsPhotochromic Properties of a Spirooxazine and a Spiropyran in Alcoholic Solutions of Zirconium and Aluminium Alkoxides: Influence of the Ethyl Acetoacetate Chelating Agent on the Optical PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2003Aurélie Lafuma Abstract The photochromism of two spiro compounds, a spiropyran and a spirooxazine, dissolved in alcoholic solutions of metal alkoxides M(OR)n (M = Zr, Al) has been studied. In the case of the aluminium alkoxide Al(OsBu)3, special photochromic behaviour is observed characteristic of complexation between the coloured form of the dyes and the aluminium. This chemical interaction induces a considerable shift in the absorption spectra and a significant retardation rate in the dark. Addition of ethyl acetoacetate, a bidentate chelate of aluminium, leads to the disappearance of this particular photochromic behaviour. (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003) [source] Phase Transformations During High-Pressure Torsion of Pure Zr and of a Zr-2.5%Nb Alloy,ADVANCED ENGINEERING MATERIALS, Issue 8 2010Alexander P. Zhilyaev Zirconium at normal conditions (room temperature and atmospheric pressure) has an HCP structure with lattice parameters a,=,3.2313,Å and c,=,5.1477,Å (,-phase). During loading under hydrostatic conditions in diamond anvil cells, a transition from the , -phase to an , -phase occurs at a pressure between 2 and 6 GPa and from , to , (bcc) at 30 GPa. It has been recently reported that the , to ,,+,, transformation might be induced by HPT processing. The resulting microstructures are stable at room temperature and atmospheric pressure. This paper explores the influence of previous processing steps and of composition in the feasibility of the HPT induced , to ,,+,, transformation. It will be shown that neither previous quenching nor high temperature HPT processing prevents the transformation from occurring during subsequent room temperature HPT. The addition of elements such as Nb also seems to favor the transformation. Understanding well the potential of HPT to stabilize high-pressure phases at normal conditions might be critical, as it will open a whole new range of applications for already existing materials. [source] Isolation of Catalytic Intermediates in Hydroamination Reactions: Insertion of Internal Alkynes into a Zirconium,Amido Bond,ANGEWANDTE CHEMIE, Issue 36 2010David Alkin dazu, und weiter geht,s: Eine Insertion ungesättigter C-C-Bindungen in M-N-Bindungen wurde als Schlüsselschritt in Reaktionen an Lanthanoidzentren und kürzlich auch in Hydroaminierungen unter Katalyse durch Gruppe-4-Metalle vorgeschlagen. Mit der im Schema gezeigten Reaktion konnten erstmals solche Zwischenstufen an einem katalytisch aktiven d0 -Metallzentrum isoliert und charakterisiert werden. [source] Non-Innocent Behavior of a Tridentate NHC Chelating Ligand Coordinated onto a Zirconium(IV) Center,ANGEWANDTE CHEMIE, Issue 12 2010Charles Romain Gar nicht unschuldig: Ein dreizähniger Bis(aryloxid)NHC-Chelatligand koordiniert leicht an ZrIV. Der resultierende Komplex geht eine neuartige THF-unterstützte Benzylwanderung vom Zirconiumzentrum zum NHC-Carben-Kohlenstoffatom ein. [source] Zirconium- and Silicon-Containing Intermediates with Three Fused Rings in a Zirconocene-Mediated Intermolecular Coupling Reaction,ANGEWANDTE CHEMIE, Issue 39 2009Wen-Xiong Zhang Prof. Die Zr/Si-haltigen Schlüsselintermediate einer Zirconocen-vermittelten intermolekularen Kupplung wurden isoliert und charakterisiert (siehe Schema). Der weitere Verbleib der funktionellen Gruppen und das Reaktionsverhalten der Zwischenstufe 1 mit etlichen ungesättigten Substraten wurden ermittelt. [source] A Rearrangement to a Zirconium,Alkenylidene in the Insertion of Dihalocarbenoids and Acetylides into Zirconacycles.CHEMINFORM, Issue 9 2007Emma Thomas 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] Zirconium Bis(amido) Catalysts for Asymmetric Intramolecular Alkene Hydroamination.CHEMINFORM, Issue 6 2007Donald A. Watson 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] Iron(III),Zirconium(IV) Combined Salt Immobilized on N-(Polystyrylbutyl)pyridinium Triflylimide as a Reusable Catalyst for a Dehydrative Esterification Reaction.CHEMINFORM, Issue 47 2006Yuka Nakamura 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] Synthesis and Crystal Structures of Zirconium(IV) Nitrate Complexes (NO2) [Zr(NO3)3(H2O)3] 2(NO3)3 (I), Cs[Zr(NO3)5] (II), and (NH4)[Zr(NO3)5](HNO3) (III).CHEMINFORM, Issue 47 2005I. V. Morozov Abstract For Abstract see ChemInform Abstract in Full Text. [source] Zirconium(IV) Chloride as a New, Highly Efficient, and Reusable Catalyst for Acetylation of Phenols, Thiols, Amines, and Alcohols under Solvent-Free Conditions.CHEMINFORM, Issue 31 2004Asit K. Chakraborti Abstract For Abstract see ChemInform Abstract in Full Text. [source] Zirconium(IV) Chloride Catalyzed New and Efficient Protocol for the Selective Cleavage of p-Methoxybenzyl Ethers.CHEMINFORM, Issue 40 2003Gangavaram V. Madhava Sharma Abstract For Abstract see ChemInform Abstract in Full Text. [source] Bonding and Bending in Zirconium(IV) and Hafnium(IV) HydrazidesCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2008Heike Herrmann Dr. Abstract Reaction of the dichloro complexes [M(N2TBSNpy)Cl2] (M=Zr: 1, Hf: 2; TBS: tBuMe2Si; py: pyridine) with one molar equivalent of LiNHNPh2 gave mixtures of the two diastereomeric chlorohydrazido(1,) complexes [M(N2TBSNpy)(NHNPh2)Cl] (M=Zr: 3,a,b, Hf: 4,a,b) in which the diphenylhydrazido(1,) ligand adopts a bent ,1 coordination. This mixture of isomers could be cleanly converted into the deep green diphenylhydrazido(2,) complexes [Zr(N2TBSNpy)(NNPh2)(py)] (5) and [Hf(N2TBSNpy)(NNPh2)(py)] (6), respectively, by dehydrohalogenation with lithium hexamethyldisilazide (LiHMDS) in the presence of one molar equivalent of pyridine. Both complexes contain a linearly coordinated hydrazinediide for which a DFT-based frontier orbital analysis established bonding through one , and two , orbitals. A high polarity of the MN bond was found, in accordance with the description of hydrazinediide(2,) acting as a six-electron donor ligand. The pyridine ligand in [M(N2TBSNpy)(NNPh2)(py)] (M=Zr: 5, Hf: 6) is substitutionally labile as established by line-shape analysis of the dynamic spectra (,G,=19,kcal,mol,1). A change in denticity of the hydrazido unit from ,1 to ,2 was studied by DFT methods. Both forms are calculated to be very close in energy and are only separated by shallow activation barriers, which supports the notion of a rapid ,1 to ,2 interconversion. This process is believed to happen early on in the NN scission in the presence of coupling reagents. Frontier orbital and natural population analyses suggest that a primarily charge-controlled nucleophilic attack at N, is unlikely whereas interaction with an electrophile could play an important role. This hypothesis was tested by the reaction of 5 and 6 with one molar equivalent of B(C6F5)3 to give [Zr(N2TBSNpy)(NNPh2){B(C6F5)3}] (7) and [Hf(N2TBSNpy)(NNPh2){B(C6F5)3}] (8). In these products, B(C6F5)3 becomes attached to the N, atom of the side-on bound hydrazinediide and there is an additional interaction of an ortho -F atom of a C6F5 ring with the metal centre. [source] Synthesis of 4H- indeno[1,2- b]thiophenes, 8H -indeno[2,1- b]-thiophenes and 8H -indeno[2,1- b]furans having acrylic acid unitJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2008Ki Joon Jeon Treatment of methyl propiolate and 2-(thiophen-2-yl)benzaldehyde, 2-(thiophen-3-yl)benzaldehyde or 2-(furan-3-yl)benzaldehyde with tetrabutylammonium iodide/zirconium (IV) chloride or treatment of methyl acrylate and the same aldehydes with 1,4-diazabicyclo[2,2,2]octane and triethanolamine induce an aldol-type reaction to furnish Baylis-Hillman adducts ,-iodo-,-(hydroxymethyl)acrylates or ,-(hydroxy-methyl)acrylates, respectively. These can be used for the preparation of indenothiophenes and indenofurans having acrylic acid unit by intramolecular Friedel-Crafts reaction with sulfuric acid in tetrachloromethane. [source] A TEM study on ZrO2 -rich phases in the quasibinary system ZrO2 -Zr3N4: Comparison between fast and slowly cooled samplesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005A. T. Tham Abstract A thorough comparison between the slowly and fast cooled ,,-type oxynitrides of zirconium has been carried out by means of transmission electron microscopy. This work aims at detecting and analyzing the so-called "modulated" ,, phase, which has been involved in the introduction of ordered anion vacancies through nitridation of zirconia. The gained information from the occurrence of such a modulated phase and the manner, in what it appears, do support the suggested structure model, which had been developed in early works in order to get a better understanding of the typical phase transitions in zirconium oxynitrides. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synthetic Explorations Towards Sterically Crowded 1,2,3-Substituted Bis(indenyl)zirconium(IV) DichloridesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2005Andreas C. Möller Abstract The systematic synthesis of 1,3-dialkyl-substituted 2-silylindenes and their suitability as zirconocene ligands is discussed. Unexpected reactivities rendered a number of substitution patterns unfeasible, especially for alkyl groups other than methyl in 2-(trimethylsilyl)indene derivatives, and essentially for all derivatives of 2-(dimethylsilyl)indene. The syntheses of rac/meso -bis[1-methyl-2-(trimethylsilyl)indenyl]zirconium(IV) dichloride (12) and bis[1,3-dimethyl-2-(trimethylsilyl)indenyl]zirconium(IV) dichloride (13b) are described. The solid-state structure of the latter displays strong deformations within the ligand framework and an unusually large Cpcentroid -Zr,Cpcentroid angle. Both, 12/MAO and 13b/MAO, displayed ethene and ethene-co-1-hexene polymerization activity. Curiously, 13b/MAO shows an extraordinary monomer selectivity, which can be rationalized by means of DFT calculations on the active site. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Iminohydroxamato Early and Late Transition Metal Halide Complexes , New Precatalysts for Aluminoxane-Cocatalyzed Olefin Insertion PolymerizationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2004Alexander Krajete Abstract We report on new families of non-metallocene metal precatalysts for olefin polymerization with titanium, zirconium, vanadium and nickel as the active metal sites. The novel ligand design concept is based on iminohydroxamic acids and their derivatives as the principal chelating units. Various anionic and neutral [N,O] and [N,N] ligand systems are easily accessible by a modular synthetic sequence of imidoyl chlorides with substituted hydroxylamines or hydrazines, respectively. Steric protection of the metal coordination site, a necessary requirement for suppression of chain termination pathways of non-metallocene catalysts, is brought about by bulky aryl substituents on the imino nitrogen atoms. Crystal structures of some of the hydroxamato ligands reveal interesting intermolecular hydrogen-bridged structures, whereas in the solid-state structure of one titanium precatalyst a five-membered chelate was observed, in line with the design principle of these systems. Preliminary ethylene polymerization studies with methylaluminoxane-activated metal complexes (M = Ti, Zr, V, Ni) show that the most active systems are [N,O]NiBr2 catalysts containing neutral O -alkyl iminohydroxamate ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Semi-Solid Processing of Tailored Aluminium-Lithium Alloys for Automotive Applications,ADVANCED ENGINEERING MATERIALS, Issue 4 2007R. Sauermann Abstract This paper describes the development and evaluation of thixoformable Al-Li-Mg-based alloys performed at the collaborative research center SFB 289, RWTH Aachen. Scandium and zirconium were added to AlLi2.1Mg5.5 (A1420) with the aid of DoE (Design of Experiments), and precursor billets were manufactured by pressure induction melting (PIM). To evaluate the thixoformability of the synthesized alloys semi-solid processed connecting rods were manufactured by the rheo container process (RCP). Subsequent heat treatment raised the mechanical properties to maximum values of tensile strength, 430,MPa, yield strength of 250,MPa, and an elongation to fracture of 13,%. The RCP process was designed for the special requirements of highly reactive alloys. The paper presents the remarkable property and process benefits of the semi-solid processing of Al-Li alloys. [source] New Metallic Glass/Alloy (MeGA) Rods Produced by Co-extrusion,ADVANCED ENGINEERING MATERIALS, Issue 10 2006S. Gravier New Metallic Glass/Alloy (MEGA)-rods with a core in bulk metallic glass (zirconium or magnesium based BMG) and a sleeve in conventional light alloys (Al-5056 and Mg-AZ31) have been elaborated by co-extrusion carried out at temperatures corresponding to the supercooled liquid region of the glass. For most glass/alloy combinations, this process leads to defect-free interfaces and therefore to good compressive strengths which can be described by the rule of mixtures. [source] Effects of metals on skin permeability barrier recoveryEXPERIMENTAL DERMATOLOGY, Issue 8 2010Mitsuhiro Denda Please cite this paper as: Effects of metals on skin permeability barrier recovery. Experimental Dermatology 2010; 19: e124,e127. Abstract:, We previously demonstrated that the electrical state of the skin surface influences epidermal permeability barrier homeostasis. At the interface between different materials, electrons are localized heterogeneously and induce electrical potential. In the present study, we evaluated the effects of metals on the barrier recovery. When we put pure gold plate on skin immediately after tape stripping, the barrier recovery rate was faster than the control. The acceleration of barrier recovery was blocked when the plate was earthed (grounded). When a plastic membrane was sandwiched between the plate and the skin, the recovery was delayed in comparison with the control. We then used a germanium diode to regulate the current flow between the plate and the earth. When the current was blocked, the barrier recovery was accelerated, but when the current was not blocked, the recovery was not accelerated. These results suggest that localization of electron might affect for the barrier recovery rate. The level of interfacial electric potential would be different due to the electrochemical property of metal. Thus, we next evaluated the effects of other metals. With samarium, zirconium, iridium and silver, the barrier recovery rate was faster than in the case of gold, while a platinum plate induced slower recovery than in the case of gold. There was a significant correlation between work function of each metal and barrier recovery rate. These results suggest that electron donation from outside accelerated the skin barrier recovery. [source] Oxidative Inorganic Multilayers for Polypyrrole Film GenerationADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Mikko Salomäki Abstract A controlled nanoscale fabrication of conducting polymer films sets severe requirements for the preparation method and substrate. A new and versatile approach for producing thin polypyrrole films on a variety of surfaces is presented. Purely inorganic thin films are first prepared from poly(metaphosphate) and tetravalent metal ions using a sequential layer-by-layer technique. Redox-active cerium(IV) polyphosphate multilayer and redox-inactive zirconium(IV) and hafnium(IV) polyphosphate multilayers are prepared. Cerium-based polyphosphate films grow exponentially with the number of layers but multilayers containing zirconium or hafnium exhibit a linear buildup process. All the studied systems produce relatively smooth films with initial bilayer thickness less than 2,nm. The cerium(IV) containing film is redox-active, which is shown by its capability to form a polypyrrole layer on its surface by oxidation of pyrrole monomers in the adjacent aqueous solution. This is a general method to produce thin oxidative films of arbitrary size and form on a wide variety of surfaces. [source] Geochemistry and petrography of basalt grindstones from the Karak Plateau, central JordanGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 1 2004Brandon G. Watts Seventeen basalt grindstone fragments from central Jordan's Karak Plateau were studied. Most of these artifacts are vesicular or amygdaloidal with calcite as the dominant mineral filling the voids. The major minerals are olivine (with iddingsite rims), plagioclase, clinopyroxene, magnetite, and apatite. Glass is present in some samples. One basalt fragment is quite different in appearance and composition and may have come from flows closer to the Dead Sea. Grindstone fragment compositions plot in the tephrite-basanite and basalt fields. A plot of the concentrations of niobium, zirconium, and yttrium reveal that the sample compositions plot in the "within-plate alkali basalt" and "within-plate tholeiite" fields. The acquisition of basalts for preparing such implements appears to have been random. Some may have been introduced through trade and migration. Archaeological and environmental studies on the Karak Plateau are urgently needed because Jordan's population growth and economic development are destroying many sites and their environmental contexts. © 2004 Wiley Periodicals, Inc. [source] Evaluation of root-end cavity preparation using ultrasonic retrotipsINTERNATIONAL ENDODONTIC JOURNAL, Issue 9 2003H. Ishikawa Abstract Aim, To evaluate and compare the efficiency of root-end preparations using ultrasonic retrotips coated with diamond and zirconium nitride. Methodology, Eighty-five extracted single-rooted teeth were root filled, and then resected 3 mm from their apices. Root-end cavities were prepared with KiS (zirconium nitride-coated retrotip), CT-5 (stainless steel tip) or diamond-coated (DC) ultrasonic retrotips, and 10 teeth served as controls. Thirty teeth were used for evaluation of the time required to prepare the root-end cavity, the number of microcracks produced on the resected surface and the number of dentinal tubule openings on the root-canal wall using scanning electron microscope (SEM) images. A further 55 teeth were used for evaluation of dye penetration following filling of the root-end cavities with Super EBA. The degree of dye penetration in millimetres was measured under the microscope after 7 days of immersion in India ink. Statistical analyses were performed using the one-way anova and Scheffe's F -test as the post hoc test. Results, There was no significant difference in the number of microcracks and dentinal tubule openings present in the root apices prepared by the three retrotips. The time required for root-end cavity preparation using the DC retrotip was significantly less than that using the other groups (P < 0.01). Positive controls showed dye penetration throughout the length of the root-end cavity, and negative controls showed no dye penetration. There was no significant difference between the three experimental groups in dye penetration. Conclusions, In this laboratory study, the time required to prepare root-end cavities using KiS retrotips was the same as that using CT-5 retrotips, and longer than that using DC retrotips. There was no significant difference in the number of microcracks or dye penetration between the three kinds of retrotips. [source] Improved Stirling engine performance through displacer surface treatmentINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2010Halit Karabulut Abstract This study intended to improve the performance of the beta-type Stirling engine, being developed by the authors for solar energy and low-grade heat sources, by means of displacer surface treatments. Three different displacers were manufactured and tested where one of them was without any surface treatment, other was zirconium coated with 0.15,mm thickness, and the other was helically knurled with 0.30,mm track depth. Because of good thermo-physical properties, helium was used as the working fluid. The heat was supplied by an LPG burner. Tests were conducted at 360±10°C hot end temperature. The highest engine power was obtained with knurled displacer as 250,W at 545,rpm speed and corresponding to this power 4.38,Nm torque was obtained. This was followed by coated and smooth displacers. Power increments provided by the knurled displacer are 40 and 60% compared with the zirconium-coated and untreated displacers. Increments of knurled displacer's torque compared with that of coated and untreated displacers are 13 and 30%, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis of Functionalized Indoles with an ,-Stereogenic Ketone Moiety Through an Enantioselective Friedel,Crafts Alkylation with (E)-1,4-Diaryl-2-butene-1,4-dionesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Gonzalo Blay Abstract Chiral complexes of BINOL-based ligands with hafnium tert -butoxide catalyze the enantioselective Friedel,Crafts alkylation of indoles with (E)-1,4-diaryl-2-butene-1,4-diones at room temperature, with good yields and ee up to 94%. Hafnium(IV) was found to be a more effective Lewis acid than other frequently used metal ions such as titanium(IV) or zirconium(IV). Unlike the enantioselective Friedel,Crafts alkylation of indoles with ,,,-unsaturated compounds where the stereogenic center is generated in the ,-position to a carbonyl group, the Friedel,Crafts alkylation with 2-butene-1,4-diones described here generates an ,-stereogenic center with respect to one of the carbonyl groups. This can be regarded as an inversion of the normal reactivity pattern or umpolung. The enantioselective Friedel,Crafts alkylation of indoles with (E)-4-oxo-4-phenylbutenoates using a zirconium(IV)-BINOL catalyst is also reported. This reaction takes place regioselectively at the carbon in the ,-position to the ketone carbonyl group, generating an ,-ester stereogenic center. [source] Silica-Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 1.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Characterization, Synthesis Abstract Various silica-supported acetylacetonate and alkoxy zirconium(IV) complexes have been prepared and characterized by quantitative chemical measurements of the surface reaction products, quantitative surface microanalysis of the surface complexes, in situ infrared spectroscopy, CP-MAS 13C,NMR spectroscopy and EXAFS. The complex (SiO)Zr(acac)3 (acac=acetylacetonate ligand) (1) can be obtained by reaction of zirconium tetraacetylacetonate [Zr(acac)4] with a silica surface previously dehydroxylated at 500,°C. The complexes (SiO)3Zr(acac) (2) and (SiO)3Zr(O- n- Bu) (n- Bu=butyl ligand) (3) can be synthesized by reaction of (SiO)3ZrH with, respectively, acetylacetone and n -butanol at room temperature. The spectroscopic data, including EXAFS spectroscopy, confirm that in compound 1 the zirconium is linked to the surface by only one SiOZr bond whereas in the case of compounds 2 and 3 the zirconium is linked to 3 surface oxygen atoms which are sigma bonded. EXAFS data indicate also that the acetylacetonate ligands behave as chelating ligands leading to a hepta-coordination around the zirconium atom in 1 and a penta-coordination in 2. In order to provide a molecular analogue of 1, the synthesis of the following polyoligosilsesquioxane derivative (c -C5H9)7Si8O12(CH3)2Zr(acac)3 (1,) was achieved. The compound 1, is obtained by reacting (c -C5H9)7Si8O11(CH3)2(OH), 4, with an equimolecular amount of Zr(acac)4. In the same manner, syntheses of complexes (c -C5H9)7Si7O12Zr(acac) (2,) and of (c-C5H9)7Si7O12Zr(O- n- Bu) (3,) were achieved by reaction of the unmodified trisilanol, (c -C5H9)7Si7O9(OH)3, with respectively Zr(acac)4 and Zr(O- n- Bu)4 at 60,°C in tetrahydrofuran. Compounds 1,, 2, and 3, can be considered as good models of 1, 2 and 3 since their spectroscopic properties are comparable with those of the surface complexes. The synthetic results obtained will permit us to study the catalytic properties of these surface complexes and of their molecular analogues with the ultimate goal of delineating clear structure-activity relationships. [source] Silica-Supported Zirconium Complexes and their Polyoligosilsesquioxane Analogues in the Transesterification of Acrylates: Part 2.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Activity, Recycling, Regeneration Abstract The catalytic activity of both supported and soluble molecular zirconium complexes was studied in the transesterification reaction of ethyl acrylate by butanol. Two series of catalysts were employed: three well defined silica-supported acetylacetonate and n -butoxy zirconium(IV) complexes linked to the surface by one or three siloxane bonds, (SiO)Zr(acac)3 (1) (SiO)3Zr(acac) (2) and (SiO)3Zr(O- n -Bu) (3), and their soluble polyoligosilsesquioxy analogues (c -C5H9)7Si8O12(CH3)2Zr(acac)3 (1,), (c -C5H9)7Si7O12Zr(acac) (2,), and (c -C5H9)7Si7O12Zr(O- n -Bu) (3,). The reactivity of these complexes were compared to relevant molecular catalysts [zirconium tetraacetylacetonate, Zr(acac)4 and zirconium tetra- n -butoxide, Zr(O- n- Bu)4]. Strong activity relationships between the silica-supported complexes and their polyoligosilsesquioxane analogues were established. Acetylacetonate complexes were found to be far superior to alkoxide complexes. The monopodal complexes 1 and 1, were found to be the most active in their respective series. Studies on the recycling of the heterogeneous catalysts showed significant degradation of activity for the acetylacetonate complexes (1 and 2) but not for the less active tripodal alkoxide catalyst, 3. Two factors are thought to contribute to the deactivation of catalyst: the lixivation of zirconium by cleavage of surface siloxide bonds and exchange reactions between acetylacetonate ligands and alcohols in the substrate/product solution. It was shown that the addition of acetylacetone to the low activity catalyst Zr(O- n- Bu)4 produced a system that was as active as Zr(acac)4. The applicability of ligand addition to heterogeneous systems was then studied. The addition of acetylacetone to the low activity solid catalyst 3 produced a highly active catalyst and the addition of a stoichiometric quantity of acetylacetone at each successive batch catalytic run greatly reduced catalyst deactivation for the highly active catalyst 1. [source] Stereoselective Synthesis of Metalated Cyclobutyl DerivativesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Einav Tsoglin Abstract Treatment of Z -vinyl carbamates with dicyclopentadienyl(diethyl)zirconium [Et2ZrCp2] leads to cyclobutyl-zirconocene derivatives in good yields and as a unique diastereoisomer. The reaction proceeds through a carbometalative ring-expansion followed by an intramolecular migratory insertion. [source] A Density Functional Study of Ethylene Insertion into the M-methyl (M = Ti, Zr) Bond for Different Catalysts, with a QM/MM Model for the Counterion, B(C6F5)3CH3,ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2002Kumar Vanka Single site homogeneous catalysts have been studied extensively in recent years as alternatives to traditional heterogeneous catalysts. The current theoretical study uses density functional theory to study the insertion process of the ethylene monomer into the titanium-carbon chain for contact ion-pair systems of the type [L1L2TiCH3 -,-CH3 -B(C6F5)3], where L1, L2, are Cp, NPH3, and other ligands. Different modes of approach cis and trans to the ,-CH3 bridge were considered. The counterion, B(C6F5)3CH3,, was modeled by QM/MM methods. The value of ,Htot,the total barrier to insertion,was found to be positive (in the range of 4,15 kcal/mol). The ability of the ancillary ligands, L1 and L2, to stabilize the ion-pair was found to be an important factor in determining the value of ,Htot. On replacing the titanium metal center with zirconium, the ,Htot values were found to be lowered (in the range of 2,9 kcal/mol), indicating that they would be better catalysts than their titanium analogues. The size of the ligands L1 and L2 was increased by replacing hydrogens in the ligands with tertiary butyl groups. The value of ,Htot was found to increase (in the range of 10,28 kcal/mol) in contrast to the simple systems, for both the cis and trans cases of approach, with the cis mode of approach giving lower values of ,Htot. Solvent effects were incorporated with cyclohexane (, = 2.023) as the solvent, and were found to have a minor influence, ±(0.5,1.5) kcal/mol) on the insertion barrier for all the cases studied. [source] 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] Comparative study of the hydrolytic degradation of glycolide/L -lactide/,-caprolactone terpolymers initiated by zirconium(IV) acetylacetonate or stannous octoateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Janusz Kasperczyk Abstract A series of copolymers have been synthesized by the ring-opening polymerization of glycolide, L -lactide, and ,-caprolactone with zirconium(IV) acetylacetonate [Zr(Acac)4] or stannous octoate [Sn(Oct)2] as the catalyst. The resulting terpolymers have been characterized by analytical techniques such as proton nuclear magnetic resonance, size exclusion chromatography, and differential scanning calorimetry. Data have confirmed that Sn(Oct)2 leads to less transesterification of polymer chains than Zr(Acac)4 under similar conditions. The various copolymers have been compression-molded and allowed to degrade in a pH 7.4 phosphate buffer at 37°C. The results show that the degradation rate depends not only on the copolymer composition but also on the chain microstructure, the Sn(Oct)2 -initiated copolymers degrading less rapidly than Zr(Acac)4 -initiated ones with more random chain structures. The caproyl component appears the most resistant to degradation as its content increases in almost all cases. Moreover, caproyl units exhibit a protecting effect on neighboring lactyl or glycolyl units. The glycolyl content exhibits different features: it decreases because of faster degradation of glycolyl units, which are more hydrophilic than caproyl and lactyl ones, remains stable in the case of abundant CGC sequences, which are very resistant to degradation, or even increases because of the formation of polyglycolide crystallites. Terpolymers can crystallize during degradation if the block length of one of the components is sufficiently long, even though they are amorphous initially. © 2007 Wiley Periodicals, Inc. 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