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141.
Acid-catalyzed polymerization of a sugar oxazoline monomer 1b having two free hydroxy groups was carried out to produce a branched aminopolysaccharide 2b. The reaction proceeded via the stereoregular glycosylation through oxazoline ring-opening process, giving rise to 2b consisting of β-glycosidic linkages. The structure of 2b was determined by the 1H NMR, 13C NMR, and IR spectra. The molecular weights determined by GPC measurements were 4200-6100. The degrees of branching were estimated by the 1H NMR spectra of the products by the reaction of 2b with 3,5-dinitrobenzoyl chloride. Deprotection of 2b was carried out by the catalytic hydrogenation in the presence of 10% Pd-C to produce a free branched aminopolysaccharide. 相似文献
142.
Izuru Takei Yoshiaki Nishibayashi Yasushi Mizobe Masanobu Hidai 《Journal of organometallic chemistry》2003,679(1):32-42
Treatment of 1-trimethylsilyloxy-1-cyclohexene (1a) in the presence of a catalytic amount of the acidic dihydrogen complex [RuCl(η2-H2)(dppe)2]OTf (4a) [dppe=1,2-bis(diphenylphosphino)ethane, OTf=OSO2CF3] (10 mol.%) under 1 atm of H2 in anhydrous ClCD2CD2Cl at 50 °C for 8 h afforded cyclohexanone (3a) and Me3SiH in quantitative NMR yields. Silyl enol ethers such as 1-triethylsilyloxy-1-cyclohexene (1b), 1-t-butyldimethylsilyloxy-1-cyclohexene (1c), and other trimethylsilylethers (1d, 1e, and 1f) reacted similarly with H2 to afford the corresponding ketones and trialkylsilanes. The direct proton transfer from H2 to the trimethylsilyl enol ethers (1a and 1d-1f) was confirmed by the experiments employing D2 gas, where α-monodeuterated ketones (3a′ and 3d′-3f′) were obtained in high yields. The enantioselective protonation of prochiral silyl enol ethers with 1 atm of H2 by employing [RuCl(η2-H2)((S)-BINAP)2]OTf (4e) [BINAP=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl] and [RuCl(η2-H2)((R, R)-CHIRAPHOS)2]OTf (4f) [CHIRAPHOS=2,3-bis(diphenylphosphino)butane] showed that no enantioselectivity was observed in either catalytic or stoichiometric protonation reactions under various reaction conditions. The reaction of [RuHCl(dppe)2] (5a) with one equivalent of Me3SiOTf under 1 atm of H2 produced rapidly 4a, concurrent with the formation of Me3SiH. Based on these studies, the mechanism for this novel hydrogenolysis of silyl enol ethers is proposed which involves heterolytic cleavage of the coordinated H2 on the ruthenium atom caused by the nucleophilic attack of the oxygen atom of enol ethers to give ketones and Me3SiOTf, and the subsequent reaction of the resultant complex 5a with Me3SiOTf under 1 atm of H2 to regenerate the original dihydrogen complex 4a. On the other hand, the stoichiometric reaction of a lithium enolate 6e with one equivalent of 4e at −78 °C in CH2Cl2 under 1 atm of H2 afforded 2-methyl-1-tetralone (3e) with 75% ee (S) in >95% yield, together with the formation of [RuHCl((S)-BINAP)2] (5e). 相似文献
143.
144.
The liquid structures of water-tetrahydrofuran (THF) and water-acetone binary mixtures were investigated by the X-ray scattering
method. Comparison of the X-ray scattering data revealed that only one kind of intermolecular water-organic molecule interaction
is commonly involved throughout all mole fractions of these liquid mixtures, in addition to the intermolecular water-water
and organic molecule-organic molecule interactions, which are present in neat water and organic liquids, respectively. On
the basis of this finding, we proposed a new analytical method for studying liquid mixtures. By this method the structural
information on the intermolecular water-organic molecule interaction as well as the concentrations of the intermolecular water-water,
water-organic molecules, and organic molecule-organic molecule interactions were obtained. Combining the concentrations of
the intermolecular water-water interaction with the concentrations of water in the liquid mixtures, the number of water-water
hydrogen bonds at various mole fractions was experimentally determined for the first time. From the dependence of the number
of water-water hydrogen bonds on the composition of the liquid mixtures, the change of the size of the self-associated water-water
clusters was deduced. 相似文献
145.
Misaki Ueda Zi Lang Goo Katsue Minami Nobuto Yoshinari Takumi Konno 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14815-14820
A 60‐nuclear silver sulfide nanocluster with a highly positive charge ( 1 ) has been synthesized by mixing an octahedral RhIII complex with 2‐aminoethanethiolate ligands, silver(I) nitrate, and d ‐penicillamine in water under mild conditions. The spherical surface of 1 is protected by the chiral octahedral RhIII complex, with cleavage of the C?S bond of the d ‐penicillamine supplying the sulfide ions. Although 1 does not contain d ‐penicillamine, it is optically active because of the enantiomeric excess of the RhIII molecules induced by chiral transfer from d ‐penicillamine. 1 can accommodate/release external Ag+ ions and replace inner Ag+ ions by Cu+ ions. The study demonstrates that a thiolato metal complex and sulfur‐containing amino acid can be used as cluster‐surface‐protecting and sulfide‐supplying regents, respectively, for creating chiral, water‐soluble, structurally precise silver sulfide nanoclusters, the properties of which are tunable through the addition/removal/exchange of Ag+ ions. 相似文献
146.
Dohi T Maruyama A Yoshimura M Morimoto K Tohma H Shiro M Kita Y 《Chemical communications (Cambridge, England)》2005,(17):2205-2207
We have synthesized new recyclable reagents having a tetraphenylmethane backbone and used them in the site-selective alpha-tosyloxylation of ketones. 相似文献
147.
Prasad GK Takei T Yonesaki Y Kumada N Kinomura N 《Journal of colloid and interface science》2005,288(1):200-204
A novel nanocomposite based on poly(N-octadecyl-2-ethynylpyridinium bromide) (PNOEtPyBr) and Mg(0.04)Nb(1.66)O5 nanosheets is synthesized by the method of exfoliation-reflocculation. The XRD data of the nanocomposite indicates the formation of Mg(0.04)Nb(1.66)O5 nanosheets/PNOEtPyBr nanostructure with an interlayer expansion of 4.6 nm along a direction perpendicular to the Mg(0.04)Nb(1.66)O5 nanosheets. Formation of this nanocomposite is further supported by the results obtained by FT-IR spectroscopy and thermogravimetry. This nanocomposite exhibits interesting dielectric properties with a dielectric constant of 18.7 F/m at 1000 Hz and 25 degrees C, which are also compared to the properties of HMg(0.34)Nb(1.66)O5 and PNOEtPyBr. 相似文献
148.
Spatially Confined Assembly of Monodisperse Ruthenium Nanoclusters in a Hierarchically Ordered Carbon Electrode for Efficient Hydrogen Evolution 下载免费PDF全文
Dr. Zhong‐Li Wang Prof. Keju Sun Dr. Joel Henzie Prof. Xianfeng Hao Dr. Cuiling Li Dr. Toshiaki Takei Prof. Yong‐Mook Kang Prof. Yusuke Yamauchi 《Angewandte Chemie (International ed. in English)》2018,57(20):5848-5852
The redox units of polyaniline (PAni) are used cooperatively, and in situ, to assemble ruthenium (Ru) nanoclusters in a hierarchically ordered carbon electrode. The oxidized quinonoid imine (QI) units in PAni bond Ru complex ions selectively, whereas reduced benzenoid amine (BA) units cannot. By electrochemically tuning the ratio of QI to BA, Ru complexes are spatially confined in the outer layer of hierarchical PAni frameworks. Carbonization of Ru‐PAni hybrids induces nucleation on the outer surface of the carbon support, generating nearly monodisperse Ru nanoclusters. The optimized catalyst has a low loading of approximately 2 wt % Ru, but exhibits a mass activity for the hydrogen evolution reaction that is about 6.8 times better than commercial 20 wt % Pt/C catalyst. 相似文献
149.
Dr. Victor Malgras Dr. Joel Henzie Dr. Toshiaki Takei Prof. Yusuke Yamauchi 《Angewandte Chemie (International ed. in English)》2018,57(29):8881-8885
Creating CsPbBr3 perovskite nanocrystals with bright blue emission is challenging because their optical properties depend sensitively on structure. Growing perovskites in mesoporous templates bypasses some of these purification issues because the size of the nanocrystal is governed by the dimensions of the pores. Mesoporous silica consisting of aligned channels with tunable diameter can be easily synthesized and used as a template. When the perovskite solution evaporates and retreats, some of the liquid remains trapped in the interconnecting pores by discontinuous dewetting. The precursor crystallizes, generating stable ca. 3.1 nm blue‐emitting perovskite nanocrystals. The mesoporous template also serves as a protective barrier to preserve the optical properties of the CsPbBr3 from atmospheric conditions. Compared to the bulk crystals and the powder composite, the strong blue‐shift of the emission peak in the film is accompanied by a decrease in the longer lifetime component and an 8‐fold increase in the external quantum efficiency. 相似文献
150.
Hirata KS Inoue K Ishida T Kajita T Kihara K Nakahata M Nakamura K Ohara S Sato N Totsuka Y Yaginuma Y Mori M Oyama Y Suzuki A Takahashi K Yamada M Suda T Tajima T Miyano K Miyata H Takei H Fukuda Y Kodera E Nagashima Y Takita M Kaneyuki K Tanimori T Beier EW Frank ED Frati W Kim SB Mann AK Newcomer FM Van Berg R Zhang W 《Physical review D: Particles and fields》1992,45(10):3355-3360