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Borane
Kinds of Borane Terms modified by Borane Selected AbstractsSelective B,H versus N,H Bond Activation in Ammonia Borane by [Ir(dppm)2]OTf,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2009Andrea Rossin Abstract Ammonia borane (AB, NH3·BH3) was activated selectively on the boron hydrogen atoms by [Ir(dppm)2]OTf, as shown by variable-temperature 31P, 11B and 1H NMR studies, to yield cis - and trans -[Ir(H)2(dppm)2]OTf dihydrides. X-ray crystal structures of these complexes were obtained. DFT calculations suggest the key reaction intermediate to be a Lewis base (L) stabilised adduct, cis -[Ir(H)(BH2·L)(dppm)2]+(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Lithium-Catalyzed Dehydrogenation of Ammonia Borane within Mesoporous Carbon Framework for Chemical Hydrogen StorageADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Li Li Abstract Ammonia borane (AB) has attracted tremendous interest for on-board hydrogen storage due to its low molecular weight and high gravimetric hydrogen capacity below a moderate temperature. However, the slow kinetics, irreversibility, and formation of volatile materials (trace borazine and ammonia) limit its practical application. In this paper, a new catalytic strategy involved lithium (Li) catalysis and nanostructure confinement in mesoporous carbon (CMK-3) for the thermal decomposition of AB is developed. AB loaded on the 5% Li/CMK-3 framework releases ,7,wt % of hydrogen at a very low temperature (around 60,°C) and entirely suppresses borazine and ammonia emissions that are harmful for proton exchange membrane fuel cells. The possible mechanism for enhanced hydrogen release via catalyzed thermal decomposition of AB is discussed. [source] ChemInform Abstract: Palladium Catalysts for Dehydrogenation of Ammonia Borane with Preferential B,H Activation.CHEMINFORM, Issue 43 2010Sung-Kwan Kim Abstract [Pd(allyl)]BF4 (I), [Pd(allyl)(2,4-hexadiene)]BF4 (II), and [Pd(MeCN)4](BF4)2 (III) catalyze the dehydrogenation of NH3BH3 most efficiently with a release of 2.0 equiv. [source] ChemInform Abstract: Synthesis of ,-Amino Alcohols via the Reduction of Lactamides Derived from Ethyl (2S)-Lactate with Borane,Methyl Sulfide.CHEMINFORM, Issue 50 2009Frank W. Lewis Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Complexes of Borane and N-Heterocyclic Carbenes: A New Class of Radical Hydrogen Atom Donor.CHEMINFORM, Issue 49 2008Shau-Hua Ueng Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Iron-Nanoparticle-Catalyzed Hydrolytic Dehydrogenation of Ammonia Borane for Chemical Hydrogen Storage.CHEMINFORM, Issue 23 2008Jun-Min Yan Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] A New and Efficient Epoxide Ring Opening via Poor Nucleophiles: Indole, p-Nitroaniline, Borane and O-Trimethylsilylhydroxylamine in Lithium Perchlorate.CHEMINFORM, Issue 45 2004Akbar Heydari No abstract is available for this article. [source] ChemInform Abstract: Exceptionally Facile Conversion of Carboxylic Acid Salts to Aldehydes by Reductive Oxidation with Borane and Pyridinium Chlorochromate.CHEMINFORM, Issue 14 2002Jin Soon Cha 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] ChemInform Abstract: Chiral Monoaminoalcohols and Diaminoalcohols of Squaric Acid: New Catalysts for the Asymmetric Reduction of Ketones by Borane.CHEMINFORM, Issue 23 2001Haibing Zhou 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] Corrigendum: Borane,Lewis Base Complexes as Homolytic Hydrogen Atom DonorsCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2010Johnny Hioe No abstract is available for this article. [source] Bimetallic Au,Ni Nanoparticles Embedded in SiO2 Nanospheres: Synergetic Catalysis in Hydrolytic Dehydrogenation of Ammonia BoraneCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2010Hai-Long Jiang Dr. Abstract Gold,nickel nanoparticles (NPs) of 3,4,nm diameter embedded in silica nanospheres of around 15,nm have been prepared by using [Au(en)2Cl3] and [Ni(NH3)6Cl2] as precursors in a NP-5/cyclohexane reversed-micelle system, and by in situ reduction in an aqueous solution of NaBH4/NH3BH3. Compared with monometallic Au@SiO2 and Ni@SiO2, the as-synthesized Au,Ni@SiO2 catalyst shows higher catalytic activity and better durability in the hydrolysis of ammonia borane, generating a nearly stoichiometric amount of hydrogen. During the generation of H2, the synergy effect between gold and nickel is apparent: The nickel species stabilizes the gold NPs and the existence of gold helps to improve the catalytic activity and durability of the nickel NPs. [source] Selective B,H versus N,H Bond Activation in Ammonia Borane by [Ir(dppm)2]OTf,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2009Andrea Rossin Abstract Ammonia borane (AB, NH3·BH3) was activated selectively on the boron hydrogen atoms by [Ir(dppm)2]OTf, as shown by variable-temperature 31P, 11B and 1H NMR studies, to yield cis - and trans -[Ir(H)2(dppm)2]OTf dihydrides. X-ray crystal structures of these complexes were obtained. DFT calculations suggest the key reaction intermediate to be a Lewis base (L) stabilised adduct, cis -[Ir(H)(BH2·L)(dppm)2]+(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Influence of Surface Chemistry on Dehydrogenation in Carbon Cryogel Ammonia Borane NanocompositesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2009Saghar Sepehri Abstract This paper reports the synthesis and characterization of boron- and nitrogen-modified carbon cryogel (CC) ammonia borane (AB) nanocomposites (BNCC-AB) for hydrogen storage. Resorcinol,formaldehyde (RF) derived CCs were modified by homogeneous dispersion of AB in RF hydrogel prior to pyrolysis. Nanocomposites were fabricated by immersing CC in the AB solution. Nitrogen sorption analysis, X-ray photoelectron spectroscopy, and differential scanning calorimetry at multiple heating rates were used to study the structure and dehydrogenation properties of the nanocomposites. The results demonstrated lower dehydrogenation temperatures and reduced activation energies for AB when confined inside pores of B- and N-modified CCs relative to AB when confined in the unmodified CC with the same pore size.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Structural and Theoretical Insights into Metal,Scorpionate Ligand ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2007Matthias Schwalbe Abstract The syntheses of the complexes [M(TmMe)(CO)2(NO)] (M = Mo, W) by reaction of NOBF4 with [M(TmMe)(CO)3], are reported and their spectroscopic characterisation and crystal structures are described. The analogous Cr complex could not be prepared by this methodology. The complexes adopt the expected pseudo-octahedral geometry. Complexes [M(L)(CO)2(NO)] (M = Cr, Mo, W; L = Cp, Tp and TmMe) together with the hypothetical [Mo(CO)2(NO)]+ cation were subjected to DFT calculations. Geometry-optimised structures closely parallel the crystallographic determinations and indicate that the complex [Cr(TmMe)(CO)2(NO)] is not inherently unstable. The DFT calculations allow the assignment of the C,O and N,O stretches in the IR spectrum and give insight into both the M,NO bonding and the metal to tripodal ligand bonding. The electron-donor strengths are confirmed to lie in the order TmMe > Tp > Cp. A side reaction of the B,H moiety of the TmMe anion with NO+ results in the isolation of the dimethylformamide adduct of (trismethimazolyl)borane, providing further evidence that the reaction pathways of the TmR ligands are more varied and less passive than in the chemistry of the nitrogen-based scorpionates.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Chelating Phosphane,Boranes as Hemilabile Ligands , Synthesis of[Mn(CO)3(,2 -H3B·dppm)][BArF4] and [Mn(CO)4(,1 -H3B·dppm)][BArF4]EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2006Nicolas Merle Abstract Manganese complexes bearing the chelating phosphane,borane ligand H3B·dppm [dppm = bis(diphenylphosphanyl)methane] have been prepared. Addition of H3B·dppm to Mn(CO)5Br using Na[BArF4] as a halide-abstracting reagent affords [Mn(CO)3(,2 -H3B·dppm)][BArF4] (1). This reacts with CO to open the bidentate borane to afford [Mn(CO)4(,1 -H3B·dppm)][BArF4] (2) in which the borane is now bound in a monodentate manner. The CO addition is reversible, and placing 2 under vacuum (hours) regenerates 1 quantitatively, demonstrating that the chelating phosphane,boranes can act as hemilabile ligands. The complexes 1 and 2 have been fully characterised by NMR spectroscopy and X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The Synthesis and Characterisation of Bis(phosphane)-Linked (6 - p -Cymene)ruthenium(II),Borane CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2005Adrian B. Chaplin Abstract The reaction of [(,6 - p -cymene)RuCl2]2 with some bis(phosphane) ligands (dppm, dppe, dppv, dppa, dpp14b, dppf) has been investigated. In general mixtures of products were obtained, although the pendant phosphane complexes [(,6 - p -cymene)RuCl2(,1 -dppv)] and [(,6 - p -cymene)RuCl2(,1 -dppa)] were isolated and characterized in the solid state by X-ray diffraction. The later complex was obtained in lower yield and undergoes an equilibration reaction resulting in the formation of a dimeric species, where the dppa bridges two ruthenium centres, and uncoordinated phosphane; the bridging species was also structurally characterised in the solid state. In contrast, the reaction of [(,6 - p -cymene)RuCl2(PPh3)] with dppa in the presence of [NH4]PF6 results in the formation of [(,6 - p -cymene)RuCl(PPh3)(,1 -dppa)]PF6, which is stable in solution. A series of linked ruthenium,borane complexes, viz. [(,6 - p -cymene)RuCl2(,1 -phosphane-BH3)] (phosphane = dppm, dppe, dppv, dppa, dpp14b, dppf) and [(,6 - p -cymene)RuCl(PPh3)(,1 -dppa-BH3)]PF6 have been prepared from isolated pendant phosphane complexes, those generated in situ, or from a preformed phosphane,borane adduct. The solid-state structures of [(,6 - p -cymene)RuCl2(,1 -dppm-BH3)], [(,6 - p -cymene)RuCl2(,1 -dppe-BH3)] and [(,6 - p -cymene)RuCl2(,1 -dppv-BH3)] have been determined by X-ray diffraction analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Designing Ionic Liquids: 1-Butyl-3-Methylimidazolium Cations with Substituted Tetraphenylborate CounterionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2003Joep van den Broeke Abstract The hydrophobic, low melting, 1-butyl-3-methylimidazolium (BMIm) salts [BMIm][BPh4] (1), [BMIm][B(C6H4Me-4)4] (2), [BMIm][B{C6H4(CF3)-4}4] (3), [BMIm][B{C6H3(CF3)2 -3,5}4] (4), [BMIm][B{C6H4(C6F13)-4}4] (5), [BMIm][B{C6H4(SiMe3)-4}4] (6), [BMIm][B(C6H4{SiMe2(CH2CH2CF3)}-4)4] (7), [BMIm][B{C6H4(SiMe2C8H17}-4}4] (8) and [BMIm][B(C6H4{SiMe2(CH2CH2C6F13)}-4)4] (9) have been prepared. Systematic variation of the substituents on the tetraphenylborate anion allowed an assessment of their influence on the physical properties of the imidazolium salts. Structural investigations using NMR and IR spectroscopy, combined with single crystal X-ray structure determinations for 2, 3, 5 and 6, revealed hydrogen-bonding interactions between the imidazolium ring protons and the borate anion, both in the solid state and in solution. These interactions are weakened upon the introduction of electron-withdrawing substituents in the anion and follow the order 3,5-(CF3)2 < ,C6F13 < ,CF3 < ,SiMe2CH2CH2C6F13 < ,SiMe2CH2CH2CF3 < ,H < ,Me < ,SiMe3. The melting points of the salts depend primarily on the bulk of the lipophilic substituents, and decrease with increasing size. Bulky lipophilic substituents dramatically enhance the solubility of the imidazolium borates 8 and 9 in hexane and reduce their relative polarity. These unique properties make imidazolium borates 8 and 9 interesting as amphiphilic ionic liquids with low polarity. Attempts to crystallise 7 resulted in decomposition. A single-crystal X-ray structure determination of the product, isolated in 6% yield, showed that a carbene,tris[4-{dimethyl(3,3,3-trifluoropropyl)silyl}phenyl]borane adduct was formed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Synthesis of Enantiopure 1- r -Aryl-2- c,5- t -diphenylphospholane Oxides and Boranes by Pd-Catalyzed C,P Bond FormationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2006Martial Toffano Abstract New chiral enantiopure phospholane oxides 1 and boranes 5 were obtained from efficient carbon,phosphorus bond formation by organocuprate or palladium-catalyzed reactions. C,P cross-coupling reactions between chiral phosphane oxide 3 or borane 4 and various aryl derivatives are presented.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis and Characterization of Ferroferriborate (Fe3BO5) NanorodsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Yi Liu Abstract Fe3BO5 nanorods with diameters from 4,nm to 16,nm and length from 43,nm to 60,nm are synthesized by a facile thermal decomposition of iron acetylacetonate and t -butylamine borane (TBAB). TBAB is used to control the 1D growth and the aspect ratio of the nanorods. These Fe3BO5 nanorods are antiferromagnetic with TN,=,174,K, which is higher than that of bulk Fe3BO5 (114,K). [source] Lithium-Catalyzed Dehydrogenation of Ammonia Borane within Mesoporous Carbon Framework for Chemical Hydrogen StorageADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Li Li Abstract Ammonia borane (AB) has attracted tremendous interest for on-board hydrogen storage due to its low molecular weight and high gravimetric hydrogen capacity below a moderate temperature. However, the slow kinetics, irreversibility, and formation of volatile materials (trace borazine and ammonia) limit its practical application. In this paper, a new catalytic strategy involved lithium (Li) catalysis and nanostructure confinement in mesoporous carbon (CMK-3) for the thermal decomposition of AB is developed. AB loaded on the 5% Li/CMK-3 framework releases ,7,wt % of hydrogen at a very low temperature (around 60,°C) and entirely suppresses borazine and ammonia emissions that are harmful for proton exchange membrane fuel cells. The possible mechanism for enhanced hydrogen release via catalyzed thermal decomposition of AB is discussed. [source] Anionic ring-opening polymerization of small phosphorus heterocycles and their borane adducts: An ab initio investigationHETEROATOM CHEMISTRY, Issue 2 2007Michelle L. Coote The kinetics and thermodynamics of anionic ring-opening reactions of phosphiranes, phosphetanes, and phospholanes and their borane adducts have been studied by high-level ab initio procedures. For the free heterocycles, model propagation reactions involving nucleophilic attack by Me2P, at the ring ,-carbon were found to be feasible for the three- and four-membered rings, but not for the five-membered ring. For the borane adducts, nucleophilic attack by Me2(BH3)P, was only facile for the three-membered ring, despite an increased thermodynamic tendency toward ring opening for the borane adducts of both the three- and four-membered rings. The formation constants of the borane adducts of methylphosphirane and methylphosphetane were K = 2.6 × 1013 L mol,1 and K = 1.2 × 1020 L mol,1, respectively. A Marcus analysis of the ring-opening reactions of methylphosphirane, methylphosphetane, and their borane adducts showed that the release of ring strain and an "additional factor" contribute to rate enhancement compared with their strain-free analogues. The additional factor was larger for the three-membered rings than for the four-membered rings and was larger in the free heterocycles than in their borane adducts. The additional factor is complex in origin and appears to reflect an increase in the separation between the bonding and antibonding orbitals of the breaking bond on going from the three-membered rings to the four-membered rings, and on going from the free heterocycles to the borane adducts. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:118,128, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20323 [source] Reaction of Bis(alkynyl)silanes with Tris(pentafluorophenyl)borane: Synthesis of Bulky Silole Derivatives by Means of 1,1-Carboboration under Mild Reaction ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009Gereon Dierker Abstract The strong Lewis acid tris(pentafluorophenyl)borane [B(C6F5)3] reacts rapidly with dimethylbis(phenylethynyl)silane (1c) at room temperature in toluene by shift of a pentafluorophenyl (C6F5) group and formation of a new carbon-bis(pentafluorophenyl)boron linkage [CB(C6F5)2] in a sequence of 1,1-carboboration reactions to yield the 4-bis(pentafluorophenyl)boryl/3-pentafluorophenyl-substituted 1,1-dimethyl-2,5-diphenylsilole derivative 7c. The analogous reaction of bis(trimethylsilylethynyl)diphenylsilane (1d) with tris(pentafluorophenyl)borane gave the corresponding boryl-substituted silole derivative (7d) featuring six bulky substituents attached at the central heterocyclic framework. Both the starting materials (1c, 1d) and the products (7c, 7d) were characterized by X-ray crystal structure analyses. [source] Synthesis of a cellulose-grafted polymeric support and its application in the reductions of some carbonyl compoundsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Poonam K. Dhiman Abstract The reduction of carbonyl compounds by borohydride supported on a cellulose,anion exchange resin is known. The synthesis of a graft copolymer of cellulose and poly(4-vinyl pyridine) [CellO- g -poly(4-VP)] has been carried out with ceric ions as a redox initiator. A postgrafting treatment of CellO- g -poly(4-VP) with sodium borohydride has produced CellO- g -poly(4-VP) borane, a polymer-supported reducing agent. Optimum conditions pertaining to the maximum percentage of grafting have been evaluated as a function of the concentrations of the initiator, monomer, and nitric acid, amount of water, time, and temperature. The maximum percentage of grafting (585%) has been obtained with 0.927 mol/L of 4-vinyl pyridine and 0.018 mol/L of ceric ammonium nitrate in 120 min at 45°C. The polymeric support, CellO- g -poly(4-VP) borane, has been used for reduction reactions of different carbonyl compounds such as benzaldehyde, cyclohexanone, crotonaldehyde, acetone, and furfural. The graft copolymer has been characterized with IR and thermogravimetric analysis. The grafted cellulose has been found to be thermally stable. The reduced products have been characterized with IR and NMR spectral methods. The reagent has been reused for the reduction of a fresh carbonyl compound, and it has been observed that the polymeric reagent reduces the compounds successfully but with a little lower product yield. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Substitution-reduction: an alternative process for the [18F]N -(2-fluoroethylation) of anilinesJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 4 2004Emmanuelle Briard Abstract Substitution of a halo atom (chloro or bromo) in easily prepared N -haloacetyl-anilines with no-carrier added (NCA) cyclotron-produced [18F]fluoride ion (18F, t1/2= 109.8 min; ,+=96.9%), followed by reduction with borane,tetrahydrofuran (BH3,THF), provides an alternative route to NCA [18F]N -(2-fluoroethyl)-anilines. This two-step and one-pot process is rapid (,50 min) and moderately high yielding (,40% decay-corrected radiochemical yield (RCY) overall). In the nucleophilic substitution reaction, 18-crown-6 is preferred to Kryptofix® 222 as complexing agent for the solubilization of the counter-ion (K+), derived from an added metal salt, in acetonitrile. Weakly basic potassium bicarbonate is preferred as the added metal salt. Inclusion of a small amount of water, equating to 4,5 molar equivalents relative to 18-crown-6, base or precursor (held in equimolar ratio), is beneficial in preventing the adsorption of radioactivity onto the wall of the glass reaction vessel and for achieving high RCY in the nucleophilic substitution reaction. BH3,THF is effective for the rapid reduction of the generated [18F]N -fluoroacetyl-aniline to the [18F]N -(2-fluoroethyl)-aniline. Copyright © 2004 John Wiley & Sons, Ltd. [source] Effect of Lewis base coordination on boryl radical reactivity: investigation using laser flash photolysis and kinetic ESRJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2009Jacques Lalevée Abstract The effect of Lewis base coordination on boryl radical reactivity (L,BH where L is triethylamine, 2-picoline, 4-dimethylaminopyridine, quinoline and diphenyl phosphine) is examined. Direct detection of the different boryl radicals, their transient absorption spectra, their interaction with double or triple bonds, oxygen, oxidizing agent, alkyl halides and their hydrogen lability have been studied using laser flash photolysis (LFP), kinetic ESR (KESR), ESR spin trapping and MO calculations. For example, a strong decrease of both the bond dissociation energy (BDE)(BH) (33.8,kcal,mol,1) and the addition rate constant to MA (1300 105 to,>105 M,1,s,1) was noted when going from the triethylamine borane to the quinoline borane complex, in line with the spin delocalization (1.04 vs. 0.19). These structures are also proposed as new highly efficient co-initiators for the acrylate photopolymerization. Copyright © 2009 John Wiley & Sons, Ltd. [source] Nickel(II) and palladium(II) complexes with ,-dioxime ligands as catalysts for the vinyl polymerization of norbornene in combination with methylaluminoxane, tris(pentafluorophenyl)borane, or triethylaluminum cocatalyst systems,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002Bernd Berchtold Abstract Nickel(II) and palladium(II) complexes with ,-dioxime ligands dimethylglyoxime, diphenylglyoxime, and 1,2-cyclohexanedionedioxime represent six new precatalysts for the polymerization of norbornene that can be activated with methylaluminoxane (MAO), the organo-Lewis acid tris(pentafluorophenyl)borane [B(C6F5)3], and triethylaluminum (TEA) AlEt3. The palladium but not the nickel precatalysts could also be activated by B(C6F5)3 alone, whereas two of the three nickel precatalysts but none of the palladium systems are somewhat active with only TEA as a cocatalyst. It was possible to achieve very high polymerization activities up to 3.2 · 107 gpolymer/molmetal · h. With the system B(C6F5)3/AlEt3, the activation process can be formulated as the following two-step reaction: (1) B(C6F5)3 and TEA lead to an aryl/alkyl group exchange and result in the formation of Al(C6F5)nEt3,n and B(C6F5)3,nEtn; and (2) Al(C6F5)nEt3,n will then react with the precatalysts to form the active species for the polymerization of norbornene. Variation of the B:Al ratio shows that Al(C6F5)Et2 is sufficient for high activation. Gel permeation chromatography indicated that it was possible to control the molar mass of poly(norbornene)s by TEA or 1-dodecene as chain-transfer agents; the molar mass can be varied in the number-average molecular weight range from 2 · 103 to 9 · 105 g · mol,1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3604,3614, 2002 [source] Synthesis of new amphiphilic diblock copolymers containing poly(ethylene oxide) and poly(,-olefin)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2002Yingying Lu Abstract This article discusses an effective route to prepare amphiphilic diblock copolymers containing a poly(ethylene oxide) block and a polyolefin block that includes semicrystalline thermoplastics, such as polyethylene and syndiotactic polystyrene (s-PS), and elastomers, such as poly(ethylene- co -1-octene) and poly(ethylene- co -styrene) random copolymers. The broad choice of polyolefin blocks provides the amphiphilic copolymers with a wide range of thermal properties from high melting temperature ,270 °C to low glass-transition temperature ,,60 °C. The chemistry involves two reaction steps, including the preparation of a borane group-terminated polyolefin by the combination of a metallocene catalyst and a borane chain-transfer agent as well as the interconversion of a borane terminal group to an anionic (O,K+) terminal group for the subsequent ring-opening polymerization of ethylene oxide. The overall reaction process resembles a transformation from the metallocene polymerization of ,-olefins to the ring-opening polymerization of ethylene oxide. The well-defined reaction mechanisms in both steps provide the diblock copolymer with controlled molecular structure in terms of composition, molecular weight, moderate molecular weight distribution (Mw/Mn < 2.5), and absence of homopolymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3416,3425, 2002 [source] Synthesis of Optically Active Polymer with P-Stereogenic Phosphine UnitsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 19 2010Yasuhiro Morisaki Abstract Optically active polymer containing P-stereogenic bisphosphine as a repeating unit in the main was successfully synthesized. A coordinated borane on the phosphorus atom could be completely removed by an organic base under mild condition, and the successive reaction with Pd afforded the corresponding polymer complex. The chirality of P-stereogenic centers was transferred to the m-phenylene-ethynylene linkers by complexation because of the prohibition of the rotary motion of the bisphosphine-Pd unit. [source] (1R,3R,4S)-1-Benzyl-3-(tert -butyldimethylsilyloxy)-4-(hydroxymethyl)pyrrolidine,borane: novel B,H...H,O hydrogen bondingACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2010Graeme J. Gainsford The absolute configuration of the title cis -(1R,3R,4S)-pyrrolidine,borane complex, C18H34BNO2Si, was confirmed. Together with the related trans isomers (3S,4S) and (3R,4R), it was obtained unexpectedly from the BH3·SMe2 reduction of the corresponding chiral (3R,4R)-lactam precursor. The phenyl ring is disordered over two conformations in the ratio 0.65:0.35. The crystallographic packing is dominated by the rarely found donor,acceptor hydroxy,borane O,H...H,B hydrogen bonds. [source] Bis(,-amine,borane) Complexes: An Unusual Binding Mode at a Transition-Metal Center,ANGEWANDTE CHEMIE, Issue 37 2009Romaeo Dallanegra Zweifaches Motiv: Bis(,-Aminboran)-Rhodium-Komplexe mit neuartigem Bindungsmotiv (zwei Aminboranliganden) wurden hergestellt (siehe Bild; Rh gelb, P grün, B rosa, N blau). Die Komplexe gehen Dehydrokupplungen unter Bildung von di- und trimeren cyclischen Aminoborylprodukten ein. [source] | ||||||||||||||||||||||||||||