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排序方式: 共有1118条查询结果,搜索用时 15 毫秒
901.
K Nozaki H Komaki Y Kawashima T Hiyama T Matsubara 《Journal of the American Chemical Society》2001,123(4):534-544
The regioselectivity of styrene insertion to an acyl-Pd bond was studied by NMR in (i) a stoichiomeric reaction and (ii) a copolymerization with CO. In the stoichiometric reaction of styrene with [(CH(3)CO)Pd(CH(3)CN)[(R,S)-BINAPHOS]].[B[3,5-(CF(3))(2)C(6)H(3)](4)], both 1,2- and 2,1-products were given. To mimic the real polymerization conditions, a polyketone-substituted complex [[CH(3)(CH(2)CHCH(3)CO)(n)]Pd[(R,S)-BINAPHOS]].[B(3,5-(CF(3))(2)C(6)H(3))(4)] (n approximately 14) was prepared. When this polymer-attached Pd species was treated with styrene, the 1,2-insertion product was the only detectable species. Thus, exclusive 1,2-insertion is demonstrated to be responsible for the styrene-CO copolymerization, in sharp contrast to the predominant 2,1-insertion with conventional nitrogen ligands. Chain-end analysis revealed that beta-hydride elimination took place from the 2,1-complex but not from the 1,2-complex. Thus, once 2,1-insertion occurs, rapid beta-hydride elimination proceeds to terminate the polymerization, as is common to the other phosphorus-ligand systems. The resulting Pd-H species re-initiates the copolymerization, as was proven by MALDI-TOF mass analysis of the product copolymers. 相似文献
902.
903.
Toshihiko Matsumoto Toshihiko Matsuoka Yoshitaka Suzuki Kenshi Miyazawa Toshikazu Kurosaki Takayuki Mizukami the late 《Macromolecular Symposia》2003,199(1):83-96
A new AB-type monomer, N,N-bistrimethylsilylated p-aminobenz-aldehyde diethyl acetal was prepared via three steps from p-bromoaniline as a starting material. The two-stage polymerization involving a soluble precursor polymer process gave a poly(p-phenylenevinylene)-type polyazomethine, poly(1,4-phenylene-nitrilomethylidyne). The first stage of polymerization was carried out in tetrahydrofuran or hexamethylphosphoramide containing water at room temperature. In the second stage, the polymer was thermally converted into the final polyazomethine by heating over 300°C to form a free-standing film. The film was reddish brown and insoluble in common organic solvents. The investigation of the first-stage products by means of MALDI-TOF mass spectroscopy proved the oligomers with 4-11 repeating units per molecule. From the 1H-NMR analysis of the model reaction, the polymerization mechanism was found to be a stepwise polycondensation of 4-diethoxymethylaniline which was formed by removal of two silyl groups of the monomer. 相似文献
904.
Hiroyuki Fujii Takeshi Sano Yoshitaka Nishio Yuji Hamada Kenichi Shibata 《Macromolecular Symposia》1998,125(1):77-82
Influence of emission sites on emission efficiency and running durability of molecular organic electroluminescent devices was investigated. When fluorescent dye rubrene was doped into TPD diamine hole transport layer, rubrene molecule emitted bright yellow light with a max. luminance of 61 000 cd/m2. The device had the highest efficiency of 9.8 Im/W at 100 cd/m2. Half-decay time of the device from initial luminance of 530 cd/m2 under constant direct current was 3 600 h. On the other hand, when rubrene was doped into BeBq2 complex electron transport layer, the efficiency was 4.4 Im/W and the half-decay time was 110 h. Thus doping site is found to exert significant influence both on the emission efficiency and the running durability. 相似文献
905.
Rui Tamura Hiroki Takahashi Ken Hirotsu Yoshitaka Nakajima Takanori Ushio Fumio Toda 《Angewandte Chemie (International ed. in English)》1998,37(20):2876-2878
Simple recrystallization of racemic (±)-NC leads to preferential enrichment of one enantiomer in the mother liquor, which allows the efficient resolution of the two enantiomers. In the unique disordered crystal structure of the racemate, the two enantiomers form centrosymmetric dimers as the major component. 相似文献
906.
Yamamoto Gen-ichiro Kyono Atsushi Sano Yoshinari Matsushita Yoshitaka Yoneda Yasuhiro 《Journal of Thermal Analysis and Calorimetry》2021,144(3):599-609
Journal of Thermal Analysis and Calorimetry - We investigated crystal structure and the local structure changes during the thermal decomposition of hydromagnesite by using in situ high-temperature... 相似文献
907.
908.
Optical Review - Visualization of an electromagnetic field distribution is helpful for spatial evaluation of field leakage and can aid in solving inverse problems of signal-source estimation.... 相似文献
909.
Yoshitaka Matsushima Moe Ishikawa Rina Shibasaki Yuki Nojima 《Tetrahedron letters》2018,59(3):231-233
A short and efficient method for synthesizing epi-cytoxazone via the corresponding oxazoline intermediate was developed. The formation of the oxazoline ring, which proceeds through an SN1 mechanism to ensure that the trans-oxazoline stereochemistry is retained, was induced by intramolecular benzylic substitution of a 1,2-bis-trichloroacetimidate, starting from the known enantiomerically pure diol. 相似文献
910.