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991.
Sylvain Koeller Dr. Joji Kadota Dr. Frédéric Peruch Dr. Alain Deffieux Dr. Noël Pinaud Isabelle Pianet Dr. Stéphane Massip Dr. Jean‐Michel Léger Dr. Jean‐Pierre Desvergne Dr. Brigitte Bibal Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(14):4196-4205
The mechanism of the ring‐opening polymerization (ROP) of lactide catalyzed by two partner hydrogen‐bonding organocatalysts was explored. New amidoindoles 4 a , c , thioamidoindoles 4 b , d , amidobenzimidazoles 5 a , c , and thioamidobenzimidazoles 5 b , c were synthesized and used as activators of the monomer. In the solid state and in solution, compounds 4 and 5 showed a propensity for self‐association, which was evaluated. (Thio)Amides 4 and 5 do catalyze the ROP of lactide in the presence of a cocatalyst, tertiary amine 3 a or 3 b , which activates the growing polymer chain through hydrogen‐bonding. Reactions were conducted in 2–24 h at 20 °C; conversion yields ranged between 22 and 100 %. A detailed study of the intermolecular interactions undertaken between the participating species showed that, as expected, simultaneous weak hydrogen bonds do exist to activate the reagents. Moreover, interactions have been revealed between the partner catalysts 4 / 5 + 3 . ROP catalyzed by these partner activators is thus governed by multiple dynamic equilibria. The latter should be judiciously adjusted to fine‐tune the catalytic properties of (thio)amides and organocatalysts, more generally. 相似文献
992.
Rajendar Bandari Dr. Thomas Höche Dr. Andrea Prager Klaus Dirnberger Dr. Michael R. Buchmeiser Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4650-4658
Monolithic polymeric supports have been prepared by electron‐beam‐triggered free‐radical polymerization using a mixture of glycidyl methacrylate and trimethylolpropane triacrylate in 2‐propanol, 1‐dodecanol, and toluene. Under appropriate conditions, phase separation occurred, which resulted in the formation of a porous monolithic matrix that was characterized by large (convective) pores in the 30 μm range as well as pores of <600 nm. The epoxy groups in pores of >7 nm were hydrolyzed by using poly(styrenesulfonic acid) (Mw=69 400 g mol?1, PDI=2.4). The remaining epoxy groups inside pores of <7 nm were subjected to aminolysis with norborn‐5‐en‐2‐ylmethylamine ( 2 ) and provided covalently bound norborn‐2‐ene (NBE) groups inside these pores. These NBE groups were then treated with the first‐generation Grubbs initiator [RuCl2(PCy3)2(CHPh)]. These immobilized Ru–alkylidenes were further used for the surface modification of the small pores by a grafting approach. A series of monomers, that is, 7‐oxanorborn‐5‐ene‐2,3‐dicarboxylic anhydride ( 3 ), norborn‐5‐ene‐2,3‐dicarboxylic anhydride ( 4 ), N,N‐di‐2‐pyridyl‐7‐oxanorborn‐5‐ene‐2‐carboxylic amide ( 5 ), N,N‐di‐2‐pyridylnorborn‐5‐ene‐2‐carboxamide ( 6 ), N‐[2‐(dimethylamino)ethyl]bicyclo[2.2.1]hept‐5‐ene‐2‐carboxamide ( 7 ), and dimethyl bicyclo[2.2.1]hept‐5‐en‐2‐ylphosphonate ( 8 ), were used for this purpose. Finally, monoliths functionalized with poly‐ 5 graft polymers were used to permanently immobilize Pd2+ and Pt4+, respectively, inside the pores. After reduction, metal nanoparticles 2 nm in diameter were formed. The palladium‐nanoparticle‐loaded monoliths were used in both Heck‐ and Suzuki‐type coupling reactions achieving turnover numbers of up to 167 000 and 63 000, respectively. 相似文献
993.
Jinzhi Liu Jun Ling Xin Li Zhiquan Shen 《Journal of molecular catalysis. A, Chemical》2009,300(1-2):59-64
The mechanism of -caprolactone (CL) insertion into a Y–OCH3 bond was investigated using density functional theory (DFT) calculations. The optimized geometries and corresponding Gibbs-free energies of the intermediates were obtained, which confirmed a four-step coordination-insertion mechanism. The coordination of CL onto yttrium center led to a nucleophilic addition of the carbonyl group of CL, followed by an intramolecular alkoxide ligand exchange. A monomer insertion was completed by the CL ring opening via acyl–oxygen bond cleavage. The formation of the five-coordinated yttrium intermediate, 3, was found to be the rate-determining step. This study could be applicable to ring-opening polymerisation (ROP) of CL initiated by lanthanide metal complexes. 相似文献
994.
Hong-Bin Zhang Xue-Lian Liang Xin Dong Hai-Yan Li Guo-Dong Lin 《Catalysis Surveys from Asia》2009,13(1):41-58
Multi-walled carbon-nanotubes (MWCNTs) are drawing increasing attention in recent years. This material possesses a series
of unique features, such as its nanometer-sized channel, highly conductive graphitized tube-wall, sp
2-C-constructed surface, and excellent performance for adsorption and spillover of hydrogen, which make the MWCNTs full of
promise to be a novel catalyst support or promoter. This article will review the recent progress in applied research of MWCNTs
as a novel promoter in heterogeneous catalysis for active components, including metals and their oxides, with the emphasis
on the study and development of MWCNT-promoted catalysts related to CO/CO2 hydrogenation to alcohols and dimethyl ether based on the recent works carried out in our laboratory. 相似文献
995.
Dai Yoshida Shuqin Han Kei‐Ichi Narita Kazuyuki Hattori Takashi Yoshida 《Macromolecular bioscience》2009,9(7):687-693
A new anhydroribotrisaccharide monomer, A2B3LR ( 1 ), was synthesized and ROP was carried out to elucidate the polymerizability and to obtain oligosaccharide‐branched polysaccharides with defined structures. The new trisaccharide monomer was found to be polymerized readily with BF3 · OEt2 as a catalyst at ?40 °C to give a lactose‐branched polymer. Copolymerization with ADBR gave the corresponding copolymers in good yields. After removal of protective benzyl groups, D ‐lactose‐branched ribofuranans with free hydroxyl groups were obtained in good yields. The structure of polymers was analyzed by 1H, 13C, and two‐dimensional NMR measurements, suggesting that D ‐lactose‐branched ribofuranans had (1 → 5)‐α stereoregularity.
996.
Edward Karakhanov Anton Maximov Sergey Kardashev Yulia Kardasheva Anna Zolotukhina Edward Rosenberg Jesse Allen 《Macromolecular Symposia》2011,304(1):55-64
Summary: Nanostructured regular materials based on cross-linked polypropylene imine (PPI) dendrimers and silica-gel polyamine composites were used as a support for the synthesis of Pd nanoparticles. The materials were tested as catalysts and displayed a high activity and selectivity for the hydrogenation of conjugated double bonds. 相似文献
997.
Organotin perfluorooctanesulfonates as air-stable Lewis acid catalysts: synthesis, characterization, and catalysis 总被引:1,自引:0,他引:1
An de L Peng Z Orita A Kurita A Man-e S Ohkubo K Li X Fukuzumi S Otera J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(6):1642-1647
The reactions of 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane and dialkyltin dihalides with silver perfluorooctanesulfonate provided the corresponding sulfonates as hydrates. The number of water molecules (n) of hydration was dependent on the conditions. The distannoxane derivative was identified as n from 0.5 to 6, while in the hydrated mononuclear species and DMSO complexes n varied widely from 4 to 13. 119Sn NMR spectroscopy and conductivity measurements indicated the ionic dissociation of these compounds in solution. These compounds exhibited unusually high solubility in polar organic solvents. The ionic dissociation together with facile hydration probably causes the unusual solubility. The Lewis acidity of these compounds was found to be high among organotin derivatives on the basis of ESR spectra of superoxide/metal-ion complexes. In contrast to well-known organotin triflates, these compounds suffered no hydrolysis upon storage in open air. The high catalytic activity of the distannoxane 1 was exemplified for various carbon-carbon bond-forming reactions, such as Mukaiyama-aldol as well as -Michael reactions and allylation of aldehydes. 相似文献
998.
Nakayama Y Saito J Bando H Fujita T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(29):7546-7556
A new and effective method for the activation, and simultaneously, immobilization of bis(phenoxyimine) early-transition-metal complexes for olefin polymerization (known as FI catalysts), which makes use of MgCl(2)/R'(n)Al(OR)(3-n) as an activator/support, has been developed. Ti-, Zr-, and V-FI catalysts combined with this MgCl(2)-based compound can form highly active MgCl(2)-supported single-site catalysts capable of demonstrating superior catalytic properties, compared to the corresponding homogeneous methylaluminoxane- (Ti- and Zr-FI catalysts) or alkylaluminum-activation systems (V-FI catalysts), in terms of their catalytic activity, molecular weight, stereoselectivity, and comonomer incorporation. Additionally, these new catalysts can produce polymers of significant morphology with high efficiency. Notably, the MgCl(2)-based compounds can also effectively activate and immobilize the early-to-late transition-metal complexes that have emerged recently. Thus, the application of MgCl(2)-based compounds as activators/supports for transition-metal complexes for olefin polymerization provides a conceptually new strategy for the development of methylaluminoxane- and borate-free, high-performance, single-site catalysts capable of controlling polymer morphology. 相似文献
999.
Hai-Yu Wang 《Journal of organometallic chemistry》2006,691(6):1275-1281
Based on two β-enaminoketonato ligands [ArNC(CH3)C(H)C(CF3)OH] (L1, Ar = 2,6-Me2C6H3; L2, Ar = 2,6-i-Pr2C6H3), their mono(β-enaminoketonato)nickel (II) complexes [(ArNC(CH3)C(H)C(CF3)O)Ni(Ph)(PPh3)] (1, Ar = 2,6-Me2C6H3; 3, Ar = 2,6-i-Pr2C6H3) and bis(β-enaminoketonato)nickel (II) complexes [(ArNC(CH3)C(H)C(CF3)O)2Ni] (2, Ar = 2,6-Me2C6H3; 4, Ar = 2,6-i-Pr2C6H3) have been synthesized and characterized. The molecular structures of complex 1, 2 and 4 have been confirmed by single-crystal X-ray analyses. After being activated with methylaluminoxane (MAO) these catalytic precursors 1-4 could polymerize norbornene to afford addition-type polynorbornene (PNB). Interestingly, catalytic activities and PNB productivity were greatly enhanced due to the introduction of strong electron-withdrawing group - trifluoro methyl into the ligands. Catalytic activities, polymer yield, Mw and Mw/Mn of PNB have been investigated under various reaction conditions. 相似文献
1000.
Luigi Busetto Pier Luigi Buldini Rita Mazzoni 《Journal of organometallic chemistry》2006,691(4):573-578
Polymer-supported alkoxycarbonylcyclopentadienyl rhodium(I) complexes have been obtained through immobilization of [Rh{C5H4CO2(CH2)2O2C-Im}(NBD)] (2) (Im = imidazole) on an (aminomethyl)polystyrene resin. An alternative approach toward the grafting of [Rh{C5H4CO2(CH2)2OH}(NBD)] (1) on a Wang resin has been also developed. Spectroscopic characterization of all the new functionalized resins with particular accent on ICP-OES measurements is presented and discussed. 相似文献