Distribution by Scientific Domains
Distribution within Chemistry

Terms modified by Cobalt

  • cobalt atom
  • cobalt catalyst
  • cobalt chloride
  • cobalt complex
  • cobalt ion
  • cobalt oxide
  • cobalt particle
  • cobalt phthalocyanine

  • Selected Abstracts

    Selective Oxidation of Acetophenones Bearing Various Functional Groups to Benzoic Acid Derivatives with Molecular Oxygen

    Ryota Nakamura
    Abstract Acetophenones substituted by alkyl, alkoxy, acetoxy, and halogen groups were selectively oxidized with molecular oxygen to the corresponding benzoic acids by using the N,N,,N,, -trihydroxyisocyanuric acid (THICA)/cobalt(II) acetate [Co(OAc)2] and THICA/Co(OAc)2/manganese(II) acetate [Mn(OAc)2]. For example, 4-methylacetophenone was selectively oxidized with molecular oxygen to 4-acetylbenzoic acid (85%) by THICA/Co(OAc)2 and to 4-methylbenzoic acid (93%) by Mn(OAc)2, while terephthalic acid was obtained in 93% with the THICA/Co(OAc)2/Mn(OAc)2 catalytic system. It is interesting that the acetyl group on the aromatic ring is efficiently converted by a very small amount of Mn(OAc)2 to the corresponding carboxylic acid, and that the present method provides a versatile route to acetylbenzoic acids which are difficult to prepare by conventional methods. [source]

    Efficient Activation of 2-Iminomethylpyridine/Cobalt-Based Alkyne [2+2+2],Cycloaddition Catalyst by Addition of a Silver Salt

    Avijit Goswami
    Abstract The addition of silver triflate (AgOTf) or silver hexafluoroantimonate (AgSbF6) significantly increased the activity of the 2-(arylimino)methylpyridine/cobalt(II) chloride hexahydrate (CoCl2,6,H2O)/zinc catalyst in alkyne cyclotrimerizations thereby accelerating the reaction and enabling the use of unactivated, simple internal alkynes as the monoyne substrate: The rate of reaction was found to be highly dependent on the nature of the counter anion (X,) and the ligand (L) in the postulated cationic cobalt(I) complex [LCo(I)]+X,. [source]

    COPPER/COBALT: Democratic Republic of Congo

    Article first published online: 4 MAY 2010
    No abstract is available for this article. [source]

    COPPER/COBALT: Democratic Republic of Congo

    Article first published online: 9 MAR 200
    No abstract is available for this article. [source]

    Hot Isostatic Pressing of Cubic Boron Nitride,Tungsten Carbide/Cobalt (cBN,WC/Co) Composites: Effect of cBN Particle Size and Some Processing Parameters on their Microstructure and Properties

    V. Martínez
    Cubic boron nitride (cBN)-cemented carbide composites have gained attraction over the last few years because of their potential uses as wear parts. The densification behavior of cBN,hard metal composites by glass encapsulation hot isostatic pressing,has been investigated. Composites with different cBN grades (from 0/0.5 to 6/12 ,m particle sizes) and cBN content (up to 50 vol%) were selected for this study. Near-full densification was obtained at temperatures between 1100° and 1200°C, and pressures between 150 and 200 MPa, respectively, while no phase transformation of cBN into the low-hardness hexagonal form has been detected by X-ray diffraction. The addition of cBN to the hard metal base material led to an increase of hardness, a significant increase of fracture toughness (KIC measured by Vickers indentation), and a moderate decrease of mechanical strength (determined by three-point bending). [source]

    P02 Analysis of coupled patch test reactions to nickel, cobalt and chromate

    CONTACT DERMATITIS, Issue 3 2004
    Janice Hegewald
    Concomitant sensitizations to Nickel, Cobalt and Chromate are often observed among patch test patients. However, the reasons for being sensitized to two or more of these substances are not completely understood. Examination of IVDK ( patch test results with multivariate procedures has been conducted to further elucidate the mechanisms involved with these sensitizations and potential exposure factors that may have led to the concomitant sensitizations. Gender, age, occupational dermatitis, and construction work were considered and examined with multivariate logistic regression models with the dependent response variable being concurrent reactions to a metal pair versus no reactions. In addition to the aforementioned anamnestic data, examination of a poly-sensitizations variable (reactions to 1, 2, or 3 standard series allergens other than Nickel, Cobalt or Chromate) provided information regarding general susceptibility to positive patch test reactions. Combined reactions to Cobalt and Chromate were strongly linked to construction work (OR = 11.23 (7.46, 16.90)) and occupational dermatitis. Female patch test patients had a higher odds of a positive patch test reaction to both Nickel and Cobalt (OR = 4.73 (3.81, 5.87)). Sensitization to other, unrelated standard series substances was associated with concurrent reactions to all of the metal pairs. The association between construction work and Cobalt-Chromate reactions corresponds with the hypothesis that cement exposures lead to cobalt-chromate sensitizations. Individual susceptibility to delayed-type sensitizations, as represented by the poly-sensitization variable, also appears to be associated with coupled sensitizations to metals and warrants further examination. [source]

    Synthesis, Structures, and Magnetic Properties of N -Trialkylsilyl-8-amidoquinoline Complexes of Chromium, Manganese, Iron, and Cobalt as well as of Wheel-Like Hexanuclear Iron(II) and Manganese(II) Bis(8-amidoquinoline)

    Astrid Malassa
    Abstract The transamination of 8-(tert -butyldimethylsilylamino)quinoline with (thf)2Cr[N(SiMe3)2]2 yields monomeric bis[8-(tert -butyldimethylsilylamido)quinoline]chromium(II) (1). Similar reactions of M[N(SiMe3)2]2 (M = Mn, Fe, Co) with 8-(trialkylsilylamino)quinoline lead to the formation of monomeric bis[8-(trialkylsilylamido)quinoline]metal(II) [M = Mn, SiR3 = SiMe2tBu (2a), SiiPr3 (2b); M = Fe, SiR3 = SiMe2tBu (3a),SiiPr3 (3b); M = Co, SiR3 = SiMe2tBu (4a), SiiPr3 (4b)]. The transamination of 8-aminoquinoline with M[N(SiMe3)2]2 (M = Mn, Fe, Co) allows the isolation of the heteroleptic 1:1 and homoleptic 2:1 products. The 1:1 complexes bis[8-amidoquinoline metal(II)bis(trimethylsilyl)amide] [M = Mn (5), Fe (6), Co (7)] are dimeric with bridging 8-amidoquinoline moieties. The 2:1 complexes of Mn and Fe, bis(8-amidoquinoline)manganese(II) (8) and bis(8-amidoquinoline)iron(II) (9), form hexamers with wheel-like molecular structures consisting of metal-centered nitrogen octahedra interconnected by common N···N edges. The cobalt complex, bis(8-amidoquinoline)cobalt(II) (10), precipitates as a microcrystalline powder. Investigations of the magnetic properties by DFT corroborate the experimental data for the Mn derivative 8, where an antiferomagnetic coupling is observed. By contrast, calculations on the Fe6 -wheel 9 yield very close-lying ferromagnetically and antiferromagnetically coupled states. [source]

    Synthesis, Structural, Thermal and Magnetic Characterization of a Pyrophosphato-Bridged Cobalt(II) Complex

    Oluwatayo F. Ikotun
    Abstract The reaction in water of CoII sulfate heptahydrate with 1,10-phenanthroline (phen) and sodium pyrophosphate (Na4P2O7) in a 2:4:1 stoichiometric ratio resulted in the crystallization of a neutral dinuclear CoII complex, {[Co(phen)2]2(,-P2O7)}·6MeOH (1), as revealed by a single-crystal X-ray diffraction study. The bridging pyrophosphato ligand between the two [Co(phen)2]2+ units in a bis(bidentate) coordination mode places the adjacent metal centers at 4.857 Å distance, and its conformation gives rise to intramolecular ,,, stacking interaction between adjacent phen ligands. Indeed, intermolecular ,,, stacking interactions between phen ligands from adjacent dinuclear complexes create a supramolecular 2D network in 1. Magnetic susceptibility measurements on a polycrystalline sample of 1 in the temperature range 1.9,295 K are typical of an overall antiferromagnetic coupling with a maximum of the magnetic susceptibility at 3.0 K. The analysis of the magnetic data in the whole temperature range allows the determination of the value of the intramolecular magnetic coupling (J = ,1.23 cm,1). The ability of the pyrophosphato ligand to mediate magnetic interactions between different first-row transition-metal ions when adopting the bis(bidentate) bridging mode is analyzed and discussed in the light of the small number of magneto-structural reports on this type of compound, bearing in mind the number of unpaired electrons and type of magnetic orbitals on each metal center. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Cobalt(III) Complexes of a Tripodal Ligand Containing Three Imidazole Groups: Properties and Structures of Racemic and Optically Active Species

    Hirofumi Nakamura
    Abstract The complex [Co(H3L)](ClO4)3·H2O (1), where H3L {tris[2-(4-imidazoylmethylideneamino)ethyl]amine} is a tripodal ligand obtained by condensation of tris(2-aminoethyl)amine and 4-formylimidazole in a 1:3 molar ratio, was synthesized and optically resolved by fractional crystallization of the diastereomeric salt with [Sb2{(R,R)-tart}2]2, [(R,R)-tart = (2R,3R)-tartrate(4,) ion]. From the less soluble part, ,-[Co(H2L)][Sb2{(R,R)-tart}2]·4H2O (2) was isolated. Starting from 2, two optically active complexes, ,-[Co(H3L)](ClO4)3·1.5H2O (,- 1) and ,-[Co(L)] (,- 3), were obtained. The crystal structures of these complexes are compared with those of the racemic structures. ,- 1 shows an unusually strong circular dichroism (, = 488 nm, ,, = ,7.74 M,1,cm,1) in the first d,d absorption band region. The effects of deprotonation,reprotonation of the uncoordinated imidazole NH groups of ,-[Co(H3L)]3+ on the UV/Vis and CD spectra and on the cyclic voltammograms were studied in methanol. Although the deprotonation,reprotonation reactions are reversible, the redox couple for the completely deprotonated species [CoIII/II(L)]0/, is not observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Cobalt and Nickel Complexes Bearing Pyrazolyliminophosphorane Ligands: Synthesis, Characterisation and Catalytic Ethylene Oligomerisation Behaviour

    Cheng Zhang
    Abstract Treatment of 1-(2,-azidophenyl)-3,5-dimethylpyrazole (1) with Ph2PR (R = Ph, Me) and (Ph2P)2CH2, respectively, affords the pyrazolyliminophosphoranes 2, 3 and 4. Reaction of 2 or 3 with [NiCl2(dme)] or NiBr2 yields the N,N-chelate nickel complexes 5,8, and with CoCl2 complexes 9 and 10. Reaction of 4 with [NiCl2(dme)], NiBr2 and CoCl2, respectively, affords the N,N,P-chelate complexes 11,13. Compounds 2,4 were characterised by 1H, 13C, 31P NMR and IR spectroscopy and elemental analysis, while complexes 5,13 were characterised by IR spectroscopy and elemental analysis. The structures of complexes 5, 9 and 12 were further characterised by single-crystal X-ray diffraction techniques. Complexes 5,13 are active catalysts for ethylene oligomerisation upon activation with alkylaluminium derivatives(Et2AlCl, MAO or MMAO). These complexes exhibit good to high catalytic activities (up to 3.54,×,106 g,mol,1,h,atm for the nickel complexes and 5.48,×,105 g,mol,1,h,atm for the cobalt complexes). The effects of varying ethylene pressure, temperature and aluminium co-catalyst/Ni or Co ratios with complexes 5, 9, 11 and 12 are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Copper, Cobalt and Platinum Complexes with Dithiothiophene-Based Ligands

    Dulce Belo
    Abstract The preparation and characterisation of new thiophenedithiolate complexes of Cu, Co and Pt with the ligands ,-tpdt and tpdt (,-tpdt = 2,3-thiophenedithiolate, tpdt = 3,4-thiophenedithiolate) is reported. The Co and Pt complexes present regular square-planar coordination geometry and low oxidation potentials when compared with complexes with simpler ligands, but their monoanionic state is found to be rather unstable. The Co(tpdt)2 complex can be isolated both in the monoanionic and dianionic states as a stable compound but the Co(,-tpdt)2 and the Pt complexes can be obtained only in the dianionic state, while their monoanionic state is unstable. The Co and Pt complexes can, however, be easily oxidised to the neutral state, giving a fine-powdered microcrystalline material without high electrical conductivity. With Cu only a less frequent geometry based on a tetrametallic CuI cluster and three ligands is observed as [Cu4(,-tpdt)3]2, and [Cu4(tpdt)3]2,. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Cobalt(II) Complexes with Substituted Salen-Type Ligands and Their Dioxygen Affinity in N,N -Dimethylformamide at Various Temperatures

    Andreas Huber
    Abstract Several unsymmetrically substituted salen-type cobalt(II) Schiff-base complexes CoL [H2L = 1,6-bis(2-hydroxyphenyl)-3,3-dimethyl-2,5-diaza-1,5-hexadiene (1); 1,6-bis(2-hydroxyphenyl)-3,3-dimethyl-2,5-diaza-1,5-heptadiene (2); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-6-(2-hydroxyphen-yl)-3,3-dimethyl-2,5-diaza-1,5-heptadiene (3); 1-(2-hydroxyphenyl)-6-methyl-2,5-diaza-1,5-nonadien-8-one (4); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-6-methyl-2,5-di-aza-1,5-nonadien-8-one (5); 1-(2-hydroxyphenyl)-3,3,6-trimethyl-2,5-diaza-1,5-nonadien-8-one (6); 1-(3- tert -butyl-2-hydroxy-5-methylphenyl)-3,3,6-trimethyl-2,5-diaza-1,5-nonadien-8-one (7)] were prepared and characterized by their UV/Vis absorption spectra, magnetic moments, and oxidation potentials. Except for complex 4 (irreversible oxidation with t½ , 3 h), complexes 1,3 and 5,7 are remarkably resistant against irreversible auto-oxidation in air-saturated N,N -dimethylformamide (DMF) at ambient temperature. To characterize the Lewis acidity of the cobalt center in 1,7, the equilibrium constant Kpy was determined for monoadduct formation with pyridine (CoL + pyCoL·py). An O2 -sensitive optode was used to determine the Henry constant, KH, for the system O2/DMF in the temperature range 298,228 K. The formation of 1:1 adducts of complexes 1,7 with O2 in DMF, as characterized by the equilibrium constant K, was followed spectrophotometrically in the temperature range 298,228 K. The parameters ,Ho, ,So, and K are reported. At 298 K, K ranges from 21.9 M,1 (5) to 155 M,1 (7). The overall spectroscopic information, including EPR spectra obtained with frozen solutions of 3 and 7 in O2 -saturated DMF, confirm that the 1:1 adducts CoL·O2 are cobalt(III) superoxo compounds. The symmetrically substituted salen complex8 [H2L = 1,6-bis(3- tert -butyl-2-hydroxy-5-methylphenyl)-3,3,4,4-tetramethyl-2,5-diaza-1,5-hexadiene in 8] is shown to catalyze the oxidation of triphenylphosphane and 2,6-di- tert -butylphenol by O2 in DMF at ambient temperature. The correlation of the data obtained for K, Kpy, and the oxidation potential E½ is discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Synthesis and Molecular Structures of Nickel(II) and Cobalt(III) Complexes with 2-(Arylimino)-3-(hydroxyimino)butane

    Ennio Zangrando
    Abstract We report new series of NiII and CoIII complexes with nitrogen-donor chelating ligands of the (E,E)-2-(arylimino)-3-(hydroxyimino)butane type (Ar,N,N,OH). These ligands are characterized by a hydrophilic (OH group) and a hydrophobic region (aryl group). NiII derivatives were obtained either as trimers of formula [Ni3(Ar,N,N,OH)3Br4(OH)][Br], with the hydrophobic groups oriented on the same side, or as bis(chelated) derivatives with cis geometry, depending on the steric hindrance of the aryl groups. CoIII complexes were obtained only as bis(chelated) derivatives, with the two ligands coplanar. The "iso -oriented" arrangement of ligands in bis(chelated) CoIII complexes is favored by weak interactions between the two ligands, namely O,H···O hydrogen bond and stacking interactions between the aryl groups. CoIII complexes might find application as catalysts for living or controlled radical polymerization of polar olefins, and preliminary results are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Resolution of Racemic N -Benzyl ,-Amino Acids by Liquid-Liquid Extraction: A Practical Method Using a Lipophilic Chiral Cobalt(III) Salen Complex and Mechanistic Studies

    Pawel Dzygiel
    Abstract The efficient resolution of racemic N -benzyl ,-amino acids (N -Bn-AA) has been achieved by a liquid-liquid extraction process using the lipophilic chiral salen,cobalt(III) complex [CoIII(3)(OAc)]. As a result of the resolution by extraction, one enantiomer (S) of the N -benzyl ,-amino acid predominated in the aqueous phase, while the other enantiomer (R) was driven into the organic phase by complexation to cobalt. The complexed amino acid (R) was then quantitatively released by a reductive (CoIII,,,CoII) counter-extraction with aqueous sodium dithionite or L -ascorbic acid in methanol. Thereductive cleavage allowed to recover the [CoII(3)] complex in good yield, which could be easily re-oxidized to[CoIII(3)(OAc)] with air/AcOH and reused with essentially no loss of reactivity and selectivity. Investigation on the nitrogen substitution indicates that the presence of a single benzyl group on the amino acid nitrogen is important to obtain high enantioselectivity in the extraction process. The kinetic vs. thermodynamic nature of the resolution process was also investigated with an enantiomeric exchange experiment, which shows that the liquid-liquid extraction with [CoIII(3)(OAc)] is an equilibrium process operating under thermodynamic control. In the absence of a suitable crystal structure of the [CoIII(3)(N -Bn-AA)] complexes, computational and spectroscopic studies were used to investigate how the N -benzyl ,-amino acids are accommodated in the "binding pocket" of the chiral cobalt complex. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Synthesis and Physicochemical Characterization of meso -Functionalized Corroles: Precursors of Organic,Inorganic Hybrid Materials

    Jean-Michel Barbe
    Abstract Cobalt(III) corroles exhibit an infinite selectivity for the coordination of carbon monoxide towards dioxygen and dinitrogen. This peculiar property thus allows their use as sensing devices for CO detection. Here are described the syntheses and physico-chemical characterization of meso mono-, bis- and tris(triethoxysilyl)-functionalized corroles, precursors of organic,inorganic materials. The corrole ring formation was achieved in every case using the "2+1" method involving the reaction of two equivalents of an encumbered dipyrromethane with one equivalent of an aromatic aldehyde in the presence of a catalytic amount of trifluoroacetic acid. The functionalization of the corrole by triethoxysilyl chains was carried out by a condensation reaction of an isocyanate, bearing a triethoxysilyl termination, either on an amino or hydroxy group. Each final compound and intermediate were characterized by various physico-chemical techniques such as 1H NMR, UV/Vis, MALDI/TOF or EI mass spectrometry and elemental analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

    Kinetically Controlled Synthesis of Hexagonally Close-Packed Cobalt Nanorods with High Magnetic Coercivity

    Yaghoub Soumare
    Abstract High-quality monodisperse metallic cobalt nanorods are obtained by the reduction of carboxylate salts of CoII in 1,2-butanediol using a rapid, simple, and solid-template-free procedure. In this polyol process, particle shape can be controlled via the growth rate, which depends on three parameters: i) the nature of the cobalt carboxylate, ii) the temperature ramp, and iii) the basicity of the medium. Cobalt in the hexagonally close-packed phase favored the growth of anisotropic particles. Magnetic measurements of the cobalt nanorods indicate they are ferromagnetic at room temperature. They have a very high coercivity of 9.0 kOe at 140,K, much higher than that observed for wires prepared with solid templates. This can be attributed to their small mean diameter and high crystallinity. [source]

    Magnetically Anisotropic Cobalt and Iron Nanofibers via Electrospinning

    ADVANCED MATERIALS, Issue 23 2007
    M. Graeser
    Magnetically anisotropic cobalt and iron nanofibers (see figure) are obtained via oriented polymer-supported electrospinning and subsequent reduction and thermal treatment. The cobalt and iron nature of the fibers is confirmed by XRD analysis. Fibers of both metals show ferromagnetic behavior. Parallel aligned iron nanofibers revealed anisotropic hysteresis loops depending on field-fiber orientation. [source]

    Highly Chemo- and Regioselective Reduction of Aromatic Nitro Compounds Catalyzed by Recyclable Copper(II) as well as Cobalt(II) Phthalocyanines

    Upendra Sharma
    Abstract Copper/cobalt phthalocyanines were established for the first time as catalysts for the very efficient chemo- and regioselective reduction of aromatic nitro compounds to generate the corresponding amines. The selective reduction of nitro compounds was observed in the presence of a large range of functional groups such as aldehyde, keto, acid, amide, ester, halogen, lactone, nitrile and heterocyclic functional groups. Furthermore, the present method was found to be highly regioselective towards the reduction of aromatic dinitro compounds in a short time with high yields. In most of the cases the conversion and selectivity were >99% as monitored by GC-MS. The reduction mechanism was elucidated by UV-vis and electrospray ionization quadrupole time-of-flight tandem mass spectrometry. [source]

    Catalytic Asymmetric Cycloaddition of Carbon Dioxide and Propylene Oxide Using Novel Chiral Polymers of BINOL-Salen- Cobalt(III) Salts

    Peng Yan
    Abstract Four new chiral polymers of BINOL-Salen-cobalt(III) salt complexes have been designed, synthesized and applied to the direct fabrication of chiral propylene carbonate from racemic propylene oxide. The (R/S)-polymer catalyst 2 and (S/R)-polymer catalyst 4 exhibit better enantioselectivity than the (R/R)-polymer catalyst 1 and the (S/S)-polymer catalyst 3 and have been recovered and reused more than ten times without loss of activity and enantioselectivity. [source]

    Hypoxia-like effect of Cobalt Chromium alloy micro particles on fibroblasts in vitro

    Bernadette K. Madathil
    Abstract Periprosthetic osteolysis leading to asceptic loosening remains the primary cause of failure of joint replacement. Although many inflammatory cell types have been implicated, the exact pathomechanisms of asceptic loosening have not been delineated. In the present study we have adopted a proteomic approach to elucidate the initial signals that are expressed to particulate material, using an in vitro cell culture system. Human lung fibroblasts MRC-5 were cultured with Cobalt Chromium (CoCr ASTM F-75, 1,7,µm) particles. Cells were harvested after 72,h incubation and total cellular proteins extracted for downstream analysis via 2D Gel Electrophoresis and tandem mass spectrometry using MALDI-TOF-TOF-MS. Thirteen protein spots showed greater than twofold increase, following 72,h incubation of fibroblast with CoCr particles. Four of these proteins were identified by tandem mass spectrometry. These were Annexin II, Pyruvate kinase, Triose phosphate isomerase, and N-myc downstream regulated gene 1 protein. Cobalt is a hypoxia mimicking agent and N-myc downstream regulated gene 1 protein, Triose phosphate isomerase, Pyruvate kinase, and Annexin II are important hypoxia regulated gene products that are found to be over expressed in cellular oxidative stress response. Our data indicates that exposure of fibroblast to CoCr alloy induces the transition of these cells into a hypoxia like state and oxidative stress even in normoxic culture conditions. The study reflects the possibility of the presence of a hypoxic environment in the periprosthetic tissue surrounding metallic implants. Published by Wiley Periodicals, Inc. J Orthop Res 28:1360,1367, 2010 [source]

    Cobalt(II) octanoate and cobalt(II) perfluorooctanoate catalyzed atom transfer radical polymerization of styrene in toluene and fluorous media,A versatile route to catalyst recycling and oligomer formation

    Marc-Stephan Weiser
    Abstract Cobalt(II) perfluorooctanoate-catalyzed atom transfer radical polymerization (ATRP) and reverse ATRP were developed to prepare oligostyrenes (Mn < 2500) with low polydispersities Mw/Mn < 1.5. Fluorous biphase catalysis was applied for effective recycling of catalyst and fluorous solvent. The homogeneous polymerization reaction was performed at 90 °C in toluene/cyclohexane/perfluorodecalin mixture (1:1:1) and fluorine-free solvents. Temperature-induced phase separation of this fluorous solvent mixture occurred at room temperature and proved to be the key for the very effective separation of the cobalt(II) perfluorooctanoate from the oligostyrene and fluorine-free solvents. Both the fluorine-tagged cobalt catalysts and the fluorous media were recycled and reused up to three times without encountering catalyst activity losses. The roles of cobalt catalysts, fluorous media, and monomer/initiator ratio were examined with respect to the polymerization kinetics. Fluorine-containing and fluorine-free cobalt(II) octanoate catalyzed controlled styrene oligomerization according to the ATRP mechanism. The molar mass control range was limited in fluorous biphase catalysis most likely because of precipitation of high molar mass polystyrenes in the fluorous reaction medium. To the best of our knowledge, this is the first time temperature-induced phase separation of fluorous and fluorine-free solvents has been successfully applied to polymerization processing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3804,3813, 2005 [source]

    Alternating Copolymerization of Carbon Dioxide and Propylene Oxide Catalyzed by Cobalt Schiff Base Complex

    Yongsheng Niu
    Abstract Cobalt 2,4-dinitrophenolate (complex 1) based upon a N,N,O,O -tetradentate Schiff base ligand framework was prepared. X-ray diffraction analysis confirmed that complex 1 was triclinic species with a six-coordinated central cobalt octahedron in the solid. Asymmetric alternating copolymerization of carbon dioxide (CO2) with racemic propylene oxide (rac -PO) proceeded effectively by complex 1 in conjunction with (4-dimethylamino)pyridine (DMAP), yielding a perfectly alternating and bimodal molecular weight distribution PO/CO2 poly(propylene carbonate) (PPC) with a small amount of cyclic carbonate byproducts. [source]

    Synthesis of Polybutadiene Nanocomposites: In situ Polymerization of 1,3-Butadiene Catalyzed by Phyllosilicate Interlayer Spacing-Confined Cobalt(II) Phosphine Complexes

    Giuseppe Leone
    Abstract Heterogeneous phyllosilicate interlayer spacing-confined cobalt catalysts were prepared by reaction of cobalt phosphine complexes with methylaluminoxane-modified clay. The catalytic systems obtained were used for the in situ polymerization of 1,3-butadiene. The polymerization taking place within the silicate galleries separates the pristine layer aggregates, allowing for the design of polybutadiene-based nanocomposites through the intercalation of the active polymerization centers. Depending on the type of cobalt complex used (i.e., type of phosphine bond to the metal) it is possible to control the microstructure (1,2 content) and the tacticity (percentage of rr, mr and mm triads) of the polymer growing directly in between the inorganic silicate host lamellae. [source]

    Uncharged Water-Soluble Metal-Bis-Porphyrins Like Molecular Tweezers for Amino Acids

    Emilio Scamporrino
    Abstract Some new water-soluble bis-porphyrins, constituted of two porphyrin units spaced by means of aliphatic bridges of different lengths, were synthesized and characterized by MALDI-TOF mass spectrometry, 1H NMR and UV-vis spectroscopy. The hydrosolubility of these uncharged compounds was guaranteed from the presence of six long PEG chains bound on the peripheral positions of the two porphyrins. Cobalt and zinc derivatives were also prepared. In the case of Co-bis-porphyrin, the appearance of induced circular dichroism (ICD) signals in water solution confirmed the formation of stable complexes with some amino acids, in which the bis-porphyrin behaves like molecular tweezers. [source]

    Novel Cobalt (II) Phthalocyanine-Containing Polyimides: Synthesis, Characterization, Thermal and Optical Properties

    Eva M. Maya
    Abstract Summary: A novel class of polymer has been prepared by reaction of a copolyimide containing carboxylic acid groups, and a cobalt phthalocyanine peripherally substituted with a reactive hydroxyl group. The incorporation of the phthalocyanine ring was achieved by esterification of the carboxylic acid groups of the polyimide with the free hydroxyl group of the phthalocyanine. In this work, a limited number of phthalocyanine rings have been introduced in order to avoid extensive modification of the copolyimide properties. The extent of modification (percentage of esterified carboxylic groups) was estimated to be about 18%. The resulting material showed good thermal stability and a high glass transition temperature (above 300,°C). The incorporation of the bulky phthalocyanine ring brought about a light decrease of thermal properties, relative to those of the initial polyimide. The presence of phthalocyanine was confirmed by the absorption band at 670 nm showing in the visible region for the modified polyimide. The novel copolyimide also exhibited a remarkable emission peak at 430 nm, when excited at 350 nm, corresponding to the emission of the cobalt phthalocyanine moiety. Schematic representation of the PI-CoPc molecule and the chemical structure of the repeat unit. [source]

    Erosion-corrosion of laser and thermally deposited coatings exposed in fluidised bed combustion plants

    A. Hjörnhede
    Abstract Coated low alloyed steel tubes were exposed in two combustion power plants of the type Circulating Fluidised Bed (CFB) and Pressurised Fluidised Bed Combustion (PFBC). The power plants were fired with wood chips and coal with a small addition of olive seeds, respectively. In addition to laser coating two thermal spray techniques were used; arc-spray (air as carrier gas) and High Velocity Oxy Fuel (HVOF). The sample locations in the PFBC plant were at the highest and lowest loops of a platen immersed in the fluidising bed. The material temperatures in each loop were 450 °C and 400 °C, respectively. The exposure lasted over two firing seasons for a total time of 8089 h. In the CFB plant a probe was located at the cyclone entrance where the material temperature was 630 °C for an exposure time of about 2100 h before being reduced to 480 °C for a further 920 h. The material wastage was determined from metallographic studies on cross-sections of rings cut from the exposed tubes. The nature and chemical composition of the corrosion products and deposits formed were determined by SEM/EDX, Auger spectroscopy, XPS and XRD. Cobalt based coatings show the best performance in both the PFBC plant and the CFB plant, while nickel based coatings are resistant to a corrosive atmosphere but very sensitive to erosion. The degree of corrosion is much larger in the CFB plant as is clearly seen from the chromium carbide containing coating, which totally degraded in this environment. Contrary the performance of the same coating was excellent in the fluidised bed due to its high erosion resistance. The material wastage of a coating with a specific composition is independent of the deposition method. No significant differences in spallation behaviour occurred among coatings deposited with the different techniques. [source]

    Increased metal allergy in patients with failed metal-on-metal hip arthroplasty and peri-implant T-lymphocytic inflammation

    ALLERGY, Issue 8 2009
    P. Thomas
    Background:, In 16 patients with revised metal-on-metal arthroplasty and peri-implant lymphocytic inflammation, we verified the role of metal hypersensitivity by patch testing (PT) and lymphocyte transformation test (LTT). Methods:, In the 16 patients with lymphocyte dominated periprosthetic inflammation, allergy history was obtained by a questionnaire, specific serum IgE to aeroallergens was measured to assess atopy, PT to standard and metal series was performed and metal sensitivity was further assessed by LTT using blood mononuclear cells. Results:, Revision surgery was performed because of pain (8/16), osteolysis (4/16), dislocation (3/16) and loosening of the stem (1/16). Histological examination showed perivascular infiltrates of T lymphocytes, high endothelial venules, fibrin exudation and accumulation of macrophages with drop-like inclusions. Five patients had a history of cutaneous metal allergy and atopy was found in 25% of the patients. In 13/16 patients (81%), systemic metal sensitivity was found based on PT and/or LTT. Patch test reactions were seen in 11/16 patients (69%; partly multiple reactions/patient): 7/16 to Cobalt (Co), 7/16 to Chromium (Cr), 4/16 to Nickel (Ni), and one each to Molybdenum (Mo) and Manganese (Mn). Ten of 16 patients (62%) showed enhanced LTT reactivity to metals: 7/16 to Ni, 7/16 to Co, 5/16 to Cr, 5/16 to Mo and 4/16 to Mn. Conclusions:, The lymphocyte dominated peri-implant inflammation may well reflect an allergic hyper-reactivity in these patients, given the high rate of concomitantly found metal allergy. Despite the overall incidence of metal implant allergy being low, allergic reactions should be included as differential diagnosis in failed metal-on-metal arthroplasty. [source]

    Cobalt-katalysierte asymmetrische Hydrovinylierung

    ANGEWANDTE CHEMIE, Issue 40 2010
    Prof. Dieter Vogt
    Zurück in die erste Reihe: Ein überraschend einfaches Verfahren unter Verwendung chiraler Diphosphan-Komplexe von Cobalt(II)-Salzen ermöglicht die hoch enantioselektive Hydrovinylierung von 1,3-Dienen mit sehr hoher Selektivität und Ausbeute (siehe Schema). [source]

    Temperature-Induced Spin-Transition in a Low-Spin Cobalt(II) Semiquinonate Complex,

    ANGEWANDTE CHEMIE, Issue 5 2010
    Michèle Graf Dr.
    Ein neuer Aspekt in der Cobaltdioxolen-Chemie: Die Herstellung und Charakterisierung des ersten Low-Spin-Cobalt(II)-Semichinonatkomplexes wird beschrieben. Der temperaturinduzierte Wechsel des Spinzustands in diesem Komplex (siehe Schema) ist nicht wie gewöhnlich mit einer Valenztautomerisierung, sondern mit einem Spin-Crossover-Prozess verknüpft. [source]

    Mechanistic Studies on the Reaction between R2N-NONOates and Aquacobalamin: Evidence for Direct Transfer of a Nitroxyl Group from R2N-NONOates to Cobalt(III) Centers,

    ANGEWANDTE CHEMIE, Issue 47 2009
    Unglaubliche Geschichten: Das Übertragen einer Nitroxylgruppe von R2N-NONOaten auf Aquacobalamin, bei dem Nitroxylcobalamin entsteht, verläuft nicht über eine H+ -katalysierte R2N-NONOat-Zersetzung, sondern wahrscheinlich über ein NONOat-Cobalamin-Intermediat (siehe Schema; r.d.s.=geschwindigkeitsbestimmender Schritt). [source]