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排序方式: 共有770条查询结果,搜索用时 31 毫秒
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Dr. Tsubasa Inokuma Prof. Dr. Ken-ichi Yamada 《Chemical record (New York, N.Y.)》2023,23(7):e202300103
Our recent efforts to develop novel N-Heterocyclic carbene (NHC)-catalyzed asymmetric reactions are described. During our investigation for development of the acylation reactions via acylazoliums generated by the reactions of NHCs and α-oxidized aldehydes, we have observed significant effects of substitution at a remote site of the carbene carbon of NHCs. In addition, we also observed a significant enhancement of the enantioselectivity by the addition of carboxylate anions. From this observation, we proposed a novel working hypothesis involving a formation of a complex of the substrate and additive to reinforce the recognition of the catalyst for enhancement of the catalytic performance of the asymmetric N-heterocyclic carbene system. By applying this concept, we achieved the kinetic resolutions of both cyclic and acyclic alcohols in excellent enantioselectivities. The effects of the remote substitution were also observed in intramolecular Stetter reaction and intermolecular benzoin reaction. In these reactions, the comparison of the catalytic performance of the NHCs bearing variable remote substitutions provided insights into the reaction mechanism because the remote substitution tuned the electronic nature of NHCs without affecting the steric and electrostatic factors around the reaction site. We also developed an intramolecular benzoin condensation involving two aldehydes, which is challenging to realize. Using the substrates bearing proper protecting groups, we succeeded in the stereo divergent synthesis of a variety of inososes, which are important intermediates for the synthesis of biologically active cyclitols. 相似文献
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Optical Review - We propose an imaging method using commercially available profile sensor. Specifically, we use a multipixel CMOS area sensor capable of acquiring projection profiles and perform... 相似文献
764.
Jianshuo Zhang Yuki Nakaya Prof. Dr. Ken-ichi Shimizu Prof. Dr. Shinya Furukawa 《Angewandte Chemie (International ed. in English)》2023,62(18):e202300744
Electric field catalysis using surface proton conduction, in which proton hopping and collision on the reactant are promoted by external electricity, is a promising approach to break the thermodynamic equilibrium limitation in endothermic propane dehydrogenation (PDH). This study proposes a catalyst design concept for more efficient electroassisted PDH at low temperature. Sm was doped into the anatase TiO2 surface to increase surface proton density by charge compensation. Pt−In alloy was deposited on the Sm-doped TiO2 for more favorable proton collision and selective propylene formation. The catalytic activity in electroassisted PDH drastically increased by doping an appropriate amount of Sm (1 mol % to Ti) where the highest propylene yield of 19.3 % was obtained at 300 °C where the thermodynamic equilibrium yield was only 0.5 %. Results show that surface proton enrichment boosts alkane dehydrogenation at low temperature. 相似文献
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Prof. Ming-Shui Yao Prof. Ken-ichi Otake Jiajia Zheng Masahiko Tsujimoto Dr. Yi-Fan Gu Lu Zheng Dr. Ping Wang Dr. Shivanna Mohana Dr. Mickaele Bonneau Tomoyuki Koganezawa Tetsuo Honma Hirotaka Ashitani Shogo Kawaguchi Prof. Yoshiki Kubota Prof. Susumu Kitagawa 《Angewandte Chemie (International ed. in English)》2023,62(35):e202308990
A one-stone, two-bird method to integrate the soft porosity and electrical properties of distinct metal–organic frameworks (MOFs) into a single material involves the design of conductive-on-insulating MOF (cMOF-on-iMOF) heterostructures that allow for direct electrical control. Herein, we report the synthesis of cMOF-on-iMOF heterostructures using a seeded layer-by-layer method, in which the sorptive iMOF core is combined with chemiresistive cMOF shells. The resulting cMOF-on-iMOF heterostructures exhibit enhanced selective sorption of CO2 compared to the pristine iMOF (298 K, 1 bar, S from 15.4 of ZIF-7 to 43.2–152.8). This enhancement is attributed to the porous interface formed by the hybridization of both frameworks at the molecular level. Furthermore, owing to the flexible structure of the iMOF core, the cMOF-on-iMOF heterostructures with semiconductive soft porous interfaces demonstrated high flexibility in sensing and electrical “shape memory” toward acetone and CO2. This behavior was observed through the guest-induced structural changes of the iMOF core, as revealed by the operando synchrotron grazing incidence wide-angle X-ray scattering measurements. 相似文献
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Dr. Qiuyi Huang Prof. Ken-ichi Otake Prof. Susumu Kitagawa 《Angewandte Chemie (International ed. in English)》2023,62(43):e202310225
The global demand for intelligent sensing of aromatic amines has consistently increased due to concerns about health and the environment. Efforts to improve material design and understand mechanisms have been made, but highly efficient non-contact sensing with host–guest structures remains a challenge. Herein, we report the first example of non-contact, high-contrast sensing of aromatic amines in a hydrogen-bonded organic framework (HOF) based on a nitro-modified stereo building block. Direct observation of binding interactions of trapped amines is achieved, leading to charge separation-induced emission quenching between host and guests. Non-contact sensing of aniline and diphenylamine is realized with quenching efficiencies up to 91.7 % and 97.0 %, which shows potential for versatile applications. This work provides an inspiring avenue to engineer multifunctional HOFs via co-crystal preparations, thus enriching applications of porous materials with explicit mechanisms. 相似文献
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