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Selected AbstractsEthene Polymerization Behavior of MAO-Activated Dichloridotitanium Complexes Bearing Bi- and Tetradentate Salicylaldimine DerivativesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2010Antti Pärssinen Abstract New chiral bridged tetradentate (N2O2)TiIVCl2 -type complexes bearing dimethylbiphenyl (1-Ti,3-Ti) and previously published binaphthyl-bridged (4-Ti) complex were synthesized with high yields. This was achieved by treating the corresponding Schiff-base ligand (H2L) precursors with Ti(NMe2)4, followed by conversion of these diamido complexes to LTiCl2 derivatives by the addition of excess of Me3SiCl. A series of unbridged titanium complexes 5-Ti,8-Ti with similar substituents at the phenoxy group were studied and their polymerization properties, after methylaluminoxane (MAO) activation, compared with the above bridged complexes. It was found that the catalysts bearing chiral tetradentate biaryl-bridged salicylaldimine ligands produce multimodal polyethylene (PE) with low activity [below 10 kgPE/(molTi,h,bar)] while their unbridged analogues provide activities that are 10,1000 times greater under similar reaction conditions. The reasons for this dramatic difference in polymerization activities are discussed based on the stabilities of the different cationic species configurations. [source] Synthesis and Properties of Organometallic PtII and PtIV Complexes with Acyclic Selenoether and Telluroether Ligands and Selenoether MacrocyclesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006William Levason Abstract The first series of planar dimethyl(selenoether)PtII complexes, [PtMe2L] [L = MeSe(CH2)nSeMe (n = 2 or 3), o -C6H4(CH2SeMe)2, [8]aneSe2 (1,5-diselenacyclooctane), or [16]aneSe4 (1,5,9,13-tetraselenacyclohexadecane)], have been obtained by treatment of [PtMe2(SMe2)2] with L in Et2O solution and characterised by VT 1H, 13C{1H}, 77Se{1H} and 195Pt{1H} NMR spectroscopy, electrospray MS and microanalysis. The corresponding dimethyl(telluroether)PtII complexes do not form under similar reaction conditions. The distorted octahedral [PtMe3I(L)] [L = o -C6H4(CH2SeMe)2, [8]aneSe2, [16]aneSe4 or MeC(CH2SeMe)3] form as stable complexes in good yield from reaction of PtMe3I with L in refluxing CHCl3 and have been characterised similarly. These all show bidentate selenoether coordination, with fast pyramidal inversion occurring at room temperature. The distorted octahedral coordination environment at PtIV is also confirmed from a crystal structure of [PtMe3I{o -C6H4(CH2SeMe)2}]. Rare examples of (telluroether)PtIV complexes, [PtMe3I{o -C6H4(CH2TeMe)2}] and the dinuclear [Me3Pt(,2 -I)2(,2 -MeTeCH2TeMe)PtMe3], have also been prepared and characterised similarly (and also by 125Te{1H} NMR spectroscopy). The [8]aneSe2 and [16]aneSe4 species are the first examples of alkyl PtII or PtIV complexes with (macro)cyclic selenoether coordination. Halide abstraction (TlPF6) from [PtMe3I(,2 -[16]aneSe4)] affords [PtMe3(,3 -[16]aneSe4)]PF6; a rare example of a cationic PtIV selenoether. The (diselenoether)PtII complexes undergo oxidative addition of MeI to yield the corresponding PtIV species [PtMe3I(diselenoether)]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Hydrogenation of Phenol in Supercritical Carbon Dioxide Catalyzed by Palladium Supported on Al-MCM-41: A Facile Route for One-Pot Cyclohexanone FormationADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009M. Chatterjee Abstract The hydrogenation of phenol has been carried out in supercritical carbon dioxide (scCO2) under very mild reaction conditions at the temperature of 50,°C over palladium supported Al-MCM-41 (metal loading ,1%). This palladium catalyst is shown to be highly active and promotes the selective formation of cyclohexanone (,98%), an industrially important compound, in a "one-pot" way. The effects of different variables like carbon dioxide and hydrogen pressure, reaction time and also silica/alumina ratio of the MCM-41 support along with palladium dispersion are presented and discussed. The pressure effect of carbon dioxide is significantly prominent in terms of conversion and cyclohexanone selectivity. Moreover, the silica/alumina ratio was also found to be an important parameter to enhance the effectiveness of the catalyst as it exhibits a remarkable increase in phenol conversion from 20.6% to 98.4% as the support changes from only silica MCM-41 to Al-MCM-41. A plausible mechanism for the hydrogenation of phenol to cyclohexanone over the palladium catalyst has been proposed. The proposition is validated by transition state calculations using density functional theory (DFT), which reveal that cyclohexanone is a favorable product and stabilized by <19,kcal,mol,1 over cyclohexanol in scCO2 medium. Under similar reaction conditions, phenol hydrogenation was also carried out with rhodium, supported on Al-MCM-41. In contrast to the palladium catalyst, a mixture of cyclohexanone (57.8%) and cyclohexanol (42.2%) was formed. Detailed characterization by X-ray diffraction and transmission electron microscopy confirmed the presence of metal nanoparticles (palladium and rhodium) between 10,20,nm. Both the catalysts exhibit strikingly different product distributions in solventless conditions compared to scCO2. This method can also be successfully applied to the other hydroxylated aromatic compounds. [source] Novel regioselective synthesis of 3,H,4H -spiro[chromene-3,2,-[1,3,4]thiadiazol]-4-one containing compoundsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2006Mohamed I. Hegab A variety of 3,,5,-diaryl-3,H,4,H -dispiro[cyclohexane-1,2,-chromene-3,,2,-[1,3,4]thiadiazol]-4,-ones 3a-c were synthesized regioselectively through the reaction of 4,H,5H -trispiro[cyclohexane-1,2,-chromene-3,,2,-[1,3,4]oxadithiino[5,6- c]chromene-5,,1,,-cyclohexan]-4,-one (1) with nitrilimines (generated in situ via triethylamine dehydrohalogenation of the corresponding hydrazonoyl chlorides 2a-c) in refluxing dry toluene. Single crystal X-ray diffraction studies of 3a,b add support for the established structure. Similarly, 3,,5,-diaryl-2,2-dimethyl-3,H,4H -spiro[chromene-3,2,-[1,3,4]thiadiazol]-4-ones 5a-c were obtained in a regioselective manner through the reaction of 2,2,5,,5,-tetramethyl-4H,5,H -spiro[chromene-3,2,-[1,3,4]oxadithiino[5,6- c]chromen]-4-one (4a) with nitrilimines under similar reaction conditions. On the other hand, reaction of 2,5,-diethyl-2,5,-dimethyl-4H,5,H -spiro[chromene-3,2,-[1,3,4]oxadithiino-[5,6- c]chromen]-4-one (4b) with nitrilimines in refluxing dry toluene afforded the corresponding 3,,5,-diaryl-2-ethyl-2-methyl-3,H,4H -spiro[chromene-3,2,-[1,3,4]thiadiazol]-4-ones 5d-f as two unisolable diastereoisomeric forms. [source] Synthesis and chemical transformation of fused tetrazoles derived from 2-bromomethyl- and 2-iodomethyl-3,5,6,7-tetrahydro-4(2H)-benzofuranonesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 4 2006Malose J. Mphahlele The 2-bromomethyl-3,5,6,7-tetrahydrobenzofuranones 1a-d were subjected to triazidochlorosilanesodium azide-mediated Schmidt rearrangement to afford the corresponding tetrazolofuroazepine derivatives 2a-dvia methylene shift. Under similar reaction conditions, the 2-iodomethyl-3,5,6,7-tetrahydrobenzofuranones 1e-h afford mixtures of the corresponding tetrazolofuroazepines 2e-h and the 4-azido-2-iodomethyl-2,3-dihydrobenzofuran derivatives 3a-c. A mechanism is proposed to account for the divergence in the reactivity of these 2-halogenomethyltetrahydrobenzofuranones (X = Br versus I). In turn, the 2-halogenomethyltetrazolofuroazepines 2a,b,d-h and the 4-azido-2-iodomethyl-2,3-dihydrobenzofurans 3a,b underwent nucleophilic substitution with triethyl phosphite and dehydrohalogenation using DBU in refluxing toluene to give the corresponding tetrazolofuroazepines 4a-d and 5a-c and benzofurans 6a,b. [source] Copolymerization of vinylcyclohexane with ethene and propene using zirconocene catalystsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2006Erkki Aitola Abstract Vinylcyclohexane (VCH) was copolymerized with ethene and propene using methylaluminoxane-activated metallocene catalysts. The catalyst precursor for the ethene copolymerization was rac -ethylenebis(indenyl)ZrCl2 (1). Propene copolymerizations were further studied with Cs -symmetric isopropylidene(cyclopentadienyl)(fluorenyl)ZrCl2 (2), C1 -symmetric ethylene(1-indenyl-2-phenyl-2-fluorenyl)ZrCl2 (3), and "meso"-dimethylsilyl[3-benzylindenyl)(2-methylbenz[e]indenyl)]ZrCl2 (4). Catalyst 1 produced a random ethene,VCH copolymer with very high activity and moderate VCH incorporation. The highest comonomer content in the copolymer was 3.5 mol %. Catalysts 1 and 4 produced poly(propene- co -vinylcyclohexane) with moderate to good activities [up to 4900 and 15,400 kg of polymer/(mol of catalyst × h) for 1 and 4, respectively] under similar reaction conditions but with fairly low comonomer contents (up to 1.0 and 2.0% for 1 and 4, respectively). Catalysts 2 and 3, both bearing a fluorenyl moiety, gave propene,VCH copolymers with only negligible amounts of the comonomer. The homopolymerization of VCH was performed with 1 as a reference, and low-molar-mass isotactic polyvinylcyclohexane with a low activity was obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6569,6574, 2006 [source] Fast living cationic polymerization accelerated by SnCl4.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2005A conventional catalyst, SnCl4, for cationic polymerization, combined with EtAlCl2 and an ester as an added base, has been used to realize the fast living cationic polymerization of not only alkyl vinyl ethers but also those containing hetero atoms in the pendant. Two important features of this system are the clearly defined roles of two Lewis acids: EtAlCl2 generates initiating species quantitatively from 1-(isobutoxy)ethyl acetate [CH3CH(OiBu)OCOCH3], and SnCl4 accelerates the polymerization, which proceeds with livingness (weight-average molecular weight/number-average molecular weight = 1.02,1.08) at a rate 103,105 greater than that with only EtAlCl2 (or Et1.5AlCl1.5). SnCl4 alone induces rapid and living-like polymerization but produces byproducts under similar reaction conditions. [source] Atom transfer radical polymerization of n -butyl acrylate catalyzed by CuBr/N -(n -hexyl)-2-pyridylmethanimineJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2002Huiqi Zhang Abstract The homogeneous atom transfer radical polymerization (ATRP) of n -butyl acrylate with CuBr/N -(n -hexyl)-2-pyridylmethanimine as a catalyst and ethyl 2-bromoisobutyrate as an initiator was investigated. The kinetic plots of ln([M]0/[M]) versus the reaction time for the ATRP systems in different solvents such as toluene, anisole, N,N -dimethylformamide, and 1-butanol were linear throughout the reactions, and the experimental molecular weights increased linearly with increasing monomer conversion and were very close to the theoretical values. These, together with the relatively narrow molecular weight distributions (polydispersity index , 1.40 in most cases with monomer conversion > 50%), indicated that the polymerization was living and controlled. Toluene appeared to be the best solvent for the studied ATRP system in terms of the polymerization rate and molecular weight distribution among the solvents used. The polymerization showed zero order with respect to both the initiator and the catalyst, probably because of the presence of a self-regulation process at the beginning of the reaction. The reaction temperature had a positive effect on the polymerization rate, and the optimum reaction temperature was found to be 100 °C. An apparent enthalpy of activation of 81.2 kJ/mol was determined for the ATRP of n -butyl acrylate, corresponding to an enthalpy of equilibrium of 63.6 kJ/mol. An apparent enthalpy of activation of 52.8 kJ/mol was also obtained for the ATRP of methyl methacrylate under similar reaction conditions. Moreover, the CuBr/N -(n -hexyl)-2-pyridylmethanimine-based system was proven to be applicable to living block copolymerization and living random copolymerization of n -butyl acrylate with methyl methacrylate. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3549,3561, 2002 [source] Coordination Chemistry of Conformation-Flexible 1,2,3,4,5,6-Cyclohexanehexacarboxylate: Trapping Various Conformations in Metal,Organic FrameworksCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2008Jing Wang Abstract To study the conformations of 1,2,3,4,5,6-cyclohexanehexacarboxylic acid (H6L), eleven new coordination polymers have been isolated from hydrothermal reactions of different metal salts with 1e,2a,3e,4a,5e,6a -cyclohexanehexacarboxylic acid (3e+3a, H6LI) and characterized. They are [Cd12(,6 - LII)(,10 - LII)3(,-H2O)6(H2O)6],16.5,H2O (1), Na12[Cd6(,6 - LII)(,6 - LIII)3],27,H2O (2), [Cd3(,13 - LII)(,-H2O)] (3), [Cd3(,6 - LIII)(2,2,-bpy)3(H2O)3],2,H2O (4), [Cd4(,4 - LVI)2(4,4,-Hbpy)4(4,4,-bpy)2(H2O)4],9.5,H2O (5), [Cd2(,6 - LII)(4,4,-Hbpy)2(H2O)10],5,H2O (6), [Cd3(,11 - LVI)(H2O)3] (7), [M3(,9 - LII)(H2O)6] (M=Mn (8), Fe (9), and Ni (10)), and [Ni4(OH)2(,10 - LII)(4,4,-bpy)(H2O)4],6,H2O (11). Three new conformations of 1,2,3,4,5,6-cyclohexanehexacarboxylate, 6e (LII), 4e+2a (LIII) and 5e+1a (LVI), have been derived from the conformational conversions of LI and trapped in these complexes by controlling the conditions of the hydrothermal systems. Complexes 1 and 2 have three-dimensional (3D) coordination frameworks with nanoscale cages and are obtained at relatively low temperatures. A quarter of the LI ligands undergo a conformational transformation into LII while the others are transformed into LIII in the presence of NaOH in 2, while all of the LI are transformed into LII in the absence of NaOH in 1. Complex 3 has a 3D condensed coordination framework, which was obtained under similar reaction conditions as 1, but at a higher temperature. The addition of 2,2,-bipyridine (2,2,-bpy) or 4,4,-bipyridine (4,4,-bpy) to the hydrothermal system as an auxiliary ligand also induces the conformational transformation of H6LI. A new LVI conformation has been trapped in complexes 4,7 under different conditions. Complex 4 has a 3D microporous supramolecular network constructed from a 2D LIII -bridged coordination layer structure by ,-, interactions between the chelating 2,2,-bpy ligands. Complexes 5,7 have different frameworks with LII/LVI conformations, which were prepared by using different amounts of 4,4,-bpy under similar synthetic conditions. Both 5 and 7 are 3D coordination frameworks involving the LVI ligands, while 6 has a 3D microporous supramolecular network constructed from a 2D LII -bridged coordination layer structure by interlayer N4,4,-HbpyH,,,O(LII) hydrogen bonds. 3D coordination frameworks 8,11 have been obtained from the H6LI ligand and the paramagnetic metal ions MnII, FeII, and NiII, and their magnetic properties have been studied. Of particular interest to us is that two copper coordination polymers of the formulae [{CuII2(,4 - LII)(H2O)4}{CuI2(4,4,-bpy)2}] (12,,) and [CuII(Hbtc)(4,4,-bpy)(H2O)],3,H2O (H3btc=1,3,5-benzenetricarboxylic acid) (12,,) resulted from the same one-pot hydrothermal reaction of Cu(NO3)2, H6LI, 4,4,-bpy, and NaOH. The Hbtc2, ligand in 12,, was formed by the in situ decarboxylation of H6LI. The observed decarboxylation of the H6LI ligand to H3btc may serve as a helpful indicator in studying the conformational transformation mechanism between H6LI and LII,VI. Trapping various conformations in metal-organic structures may be helpful for the stabilization and separation of various conformations of the H6L ligand. [source] Acid,Base Bifunctional Catalysis of Silica,Alumina-Supported Organic Amines for Carbon,Carbon Bond-Forming ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2008Ken Motokura Dr. Abstract Acid,base bifunctional heterogeneous catalysts were prepared by the reaction of an acidic silica,alumina (SA) surface with silane-coupling reagents possessing amino functional groups. The obtained SA-supported amines (SA,NR2) were characterized by solid-state 13C and 29Si,NMR spectroscopy, FT-IR spectroscopy, and elemental analysis. The solid-state NMR spectra revealed that the amines were immobilized by acid,base interactions at the SA surface. The interactions between the surface acidic sites and the immobilized basic amines were weaker than the interactions between the SA and free amines. The catalytic performances of the SA,NR2 catalysts for various carbon,carbon bond-forming reactions, such as cyano-ethoxycarbonylation, the Michael reaction, and the nitro-aldol reaction, were investigated and compared with those of homogeneous and other heterogeneous catalysts. The SA,NR2 catalysts showed much higher catalytic activities for the carbon,carbon bond-forming reactions than heterogeneous amine catalysts using other supports, such as SiO2 and Al2O3. On the other hand, homogeneous amines hardly promoted these reactions under similar reaction conditions, and the catalytic behavior of SA,NR2 was also different from that of MgO, which was employed as a typical heterogeneous base. An acid,base dual-activation mechanism for the carbon,carbon bond-forming reactions is proposed. [source] | ||||||||||