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排序方式: 共有1333条查询结果,搜索用时 15 毫秒
1.
2.
Proton Order–Disorder Phenomena in a Hydrogen‐Bonded Rhodium–η5‐Semiquinone Complex: A Possible Dielectric Response Mechanism 下载免费PDF全文
Dr. Minoru Mitsumi Kazunari Ezaki Yuuki Komatsu Prof. Dr. Koshiro Toriumi Dr. Tatsuya Miyatou Prof. Dr. Motohiro Mizuno Nobuaki Azuma Prof. Dr. Yuji Miyazaki Prof. Dr. Motohiro Nakano Prof. Dr. Yasutaka Kitagawa Dr. Takayasu Hanashima Dr. Ryoji Kiyanagi Dr. Takashi Ohhara Prof. Dr. Kazuhiro Nakasuji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9682-9696
A newly synthesized one‐dimensional (1D) hydrogen‐bonded (H‐bonded) rhodium(II)–η5‐semiquinone complex, [Cp*Rh(η5‐p‐HSQ‐Me4)]PF6 ([ 1 ]PF6; Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl; HSQ=semiquinone) exhibits a paraelectric–antiferroelectric second‐order phase transition at 237.1 K. Neutron and X‐ray crystal structure analyses reveal that the H‐bonded proton is disordered over two sites in the room‐temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF6? ion. The relative permittivity εb′ along the H‐bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of 13C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low‐temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10?4–10?6 s in the temperature range of 240–270 K. DFT calculations predict that the protonation/deprotonation of [ 1 ]+ leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π‐bonded rhodium fragment, producing the stable η6‐hydroquinone complex, [Cp*Rh3+(η6‐p‐H2Q‐Me4)]2+ ([ 2 ]2+), and η4‐benzoquinone complex, [Cp*Rh+(η4‐p‐BQ‐Me4)] ([ 3 ]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [ 2 ]2+ and [ 3 ], which would be generated in the H‐bonded chain. 相似文献
3.
This work examines the ozone electrogeneration(OE) at a binary coating of different nominal compositions(Pt)x-(TaOy)(100-x), where x(percentage in the precursor solution) varied between 1% and 100%, coated on titanium substrate prepared by a sol-gel technique. TheOE is performed in an artificial tap water at room temperature(25C). The percentages of Pt and TaOy in the coating significantly affect the electrocatalytic activity towards oxygen evolution. The oxygen evolution was retarded to a different extent based on the electrode composition. The largest retardation was obtained at the(Pt)10-(TaOy)90 electrode(ca. 480 m V positive shift) as compared with the(Pt)100-(TaOy)0 electrode.This was reflected in a high current efficiency(CE) ofOE(ca. 19.3%) at the former electrode. This value is considered to be among the highest values reported forOE at 25C in neutral media. The composite electrodes were characterized by voltammetric and surface techniques. A plausible explanation for the change of the efficiency ofOE with the electrode composition is given based on the electrochemical results. 相似文献
4.
Junki Ochi Kazuhiro Yuhara Prof. Kazuo Tanaka Prof. Yoshiki Chujo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(20):e202200155
It is still challenging to realize a dual-emission system, in which two luminescent bands simultaneously appear by photoexcitation, in solid with organic dyes due to the difficulty in regulation of electronic properties in the excited state and concentration quenching. o-Carborane is known to be a versatile platform for constructing solid-state emitters since the sphere boron cluster is favorable for suppressing intermolecular interactions and subsequently concentration quenching. Here, we show solid-state dual-emissive o-carborane derivatives. We prepared 4 types of o-carborane derivatives and found dual-emission behaviors both in solution and solid states. By regulating the rotation at the o-carborane unit with the intramolecular CcageH⋅⋅⋅O interaction, the dual-emission intensity ratios were changed. Finally, it was demonstrated that the overall photoluminescence spectra can be estimated using the binding energy of intramolecular interactions. 相似文献
5.
Dr. Trapti Aggarwal Kenshiro Hada Yusuke Murata Dr. Yuji Sumii Kazuhiro Tanagawa Kiyoteru Niina Soichiro Mori Dr. Jorge Escorihuela Prof. Dr. Norio Shibata 《Angewandte Chemie (International ed. in English)》2023,62(33):e202307090
Alkyne hydroamination is an effective approach for the production of enamines and enamine-containing N-heterocycles. However, stereoselectivity control is a considerable challenge in this reaction because of the electronic repulsion between an incoming nitrogen lone pair and the alkyne π-system. Herein, we propose a methodology involving β-regio- and Z-selective alkyne hydroamination by using tetrafluoro-λ6-sulfanyl (SF4) alkynes under superbasic, naked anion conditions. The reaction is compatible with a wide variety of N-heterocycles, including indoles, carbazoles, pyrazoles, and imidazoles, and selectively furnishes SF4-linked Z-vinyl enamines with β-regioselectively. Moreover, the method can be extended to the β- and Z-controlled, base-mediated alkyne hydrophenoxylation with phenols to provide SF4-linked Z-vinyl ethers in high yields. As the SF4 unit has attracted attention as a bioisostere for alkynes, p-benzenes, bicyclo[1.1.1]pentyl (BCP) groups, and cubanes in medicinal chemistry, this chemistry represents an effective approach to creating novel drug candidates incorporating SF4-containing molecules. 相似文献
6.
Back Cover: CH Activation Generates Period‐Shortening Molecules That Target Cryptochrome in the Mammalian Circadian Clock (Angew. Chem. Int. Ed. 24/2015) 下载免费PDF全文
Tsuyoshi Oshima Dr. Iori Yamanaka Dr. Anupriya Kumar Dr. Junichiro Yamaguchi Dr. Taeko Nishiwaki‐Ohkawa Kei Muto Rika Kawamura Dr. Tsuyoshi Hirota Prof. Dr. Kazuhiro Yagita Prof. Dr. Stephan Irle Prof. Dr. Steve A. Kay Prof. Dr. Takashi Yoshimura Prof. Dr. Kenichiro Itami 《Angewandte Chemie (International ed. in English)》2015,54(24):7200-7200
7.
Masashi Shigenobu Kazuhiro Takenaka Hiroaki Sasai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(33):9708-9712
A palladium‐catalyzed direct arylation of isoxazoles with aryl iodides has been achieved. The C H bond at the 5‐position is activated selectively to give coupling products in moderate to good yields. This direct arylation was applied to the synthesis of a spiro‐type chiral ligand, which proved to be most effective to the palladium‐catalyzed tandem cyclization of a dialkenyl alcohol. 相似文献
8.
One‐Pot Synthesis of 3‐Acetyl‐2‐aryl‐3,4‐dihydroquinazolines from N‐[2‐(Azidomethyl)phenyl]benzamides Utilizing Intramolecular Aza‐Wittig Reaction 下载免费PDF全文
Kazuhiro Kobayashi Naoki Matsumoto Mika Nagashima Hiroki Inouchi 《Helvetica chimica acta》2015,98(2):184-189
A new and convenient method for the preparation of 3,4‐dihydroquinazolines 5 with aryl and Ac groups at C(2) and N(3), respectively, has been developed. The key sequence is the formation of aza‐phosphorane intermediates by the reaction of N‐[2‐(azidomethyl)phenyl]benzamides 1 with Ph3P, followed by intramolecular aza‐Wittig reaction and 3‐acetylation, which can be conducted in one‐pot. 相似文献
9.
Spontaneous Formation of Microgroove Arrays on the Surface of p‐Type Porous Silicon Induced by a Turing Instability in Electrochemical Dissolution 下载免费PDF全文
Prof. Dr. Kazuhiro Fukami Tomoko Urata Prof. Dr. Katharina Krischer Prof. Dr. Naoya Nishi Prof. Dr. Tetsuo Sakka Dr. Atsushi Kitada Prof. Dr. Kuniaki Murase 《Chemphyschem》2015,16(8):1613-1618
Self‐organization plays an imperative role in recent materials science. Highly tunable, periodic structures based on dynamic self‐organization at micrometer scales have proven difficult to design, but are desired for the further development of micropatterning. In the present study, we report a microgroove array that spontaneously forms on a p‐type silicon surface during its electrodissolution. Our detailed experimental results suggest that the instability can be classified as Turing instability. The characteristic scale of the Turing‐type pattern is small compared to self‐organized patterns caused by the Turing instabilities reported so far. The mechanism for the miniaturization of self‐organized patterns is strongly related to the semiconducting property of silicon electrodes as well as the dynamics of their surface chemistry. 相似文献
10.
Inside Cover: Spontaneous Formation of Microgroove Arrays on the Surface of p‐Type Porous Silicon Induced by a Turing Instability in Electrochemical Dissolution (ChemPhysChem 8/2015) 下载免费PDF全文