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991.
Prof. Dr. Pavel Kočovský Prof. Dr. Jan‐E. Bäckvall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):36-56
In this review the stereochemistry of palladium‐catalyzed addition of nucleophiles to alkenes is discussed, and examples of these reactions in organic synthesis are given. Most of the reactions discussed involve oxygen and nitrogen nucleophiles; the Wacker oxidation of ethylene has been reviewed in detail. An anti‐hydroxypalladation in the Wacker oxidation has strong support from both experimental and computational studies. From the reviewed material it is clear that anti‐addition of oxygen and nitrogen nucleophiles is strongly favored in intermolecular addition to olefin–palladium complexes even if the nucleophile is coordinated to the metal. On the other hand, syn‐addition is common in the case of intramolecular oxy‐ and amidopalladation as a result of the initial coordination of the internal nucleophile to the metal. 相似文献
992.
993.
Li Ma Qian Wang Dr. Wai‐Lun Man Dr. Hoi‐Ki Kwong Dr. Chi‐Chiu Ko Prof. Tai‐Chu Lau 《Angewandte Chemie (International ed. in English)》2015,54(17):5246-5249
The study of manganese complexes as water‐oxidation catalysts (WOCs) is of great interest because they can serve as models for the oxygen‐evolving complex of photosystem II. In most of the reported Mn‐based WOCs, manganese exists in the oxidation states III or IV, and the catalysts generally give low turnovers, especially with one‐electron oxidants such as CeIV. Now, a different class of Mn‐based catalysts, namely manganese(V)–nitrido complexes, were explored. The complex [MnV(N)(CN)4]2− turned out to be an active homogeneous WOC using (NH4)2[Ce(NO3)6] as the terminal oxidant, with a turnover number of higher than 180 and a maximum turnover frequency of 6 min−1. The study suggests that active WOCs may be constructed based on the MnV(N) platform. 相似文献
994.
Rhodium(II)‐Catalyzed Cycloaddition Reactions of Non‐classical 1,5‐Dipoles for the Formation of Eight‐Membered Heterocycles 下载免费PDF全文
Dong Jin Lee Donguk Ko Prof. Eun Jeong Yoo 《Angewandte Chemie (International ed. in English)》2015,54(46):13715-13718
A new type of intermolecular rhodium(II)‐catalyzed [5+3] cycloaddition has been developed. This higher‐order cycloaddition between pyridinium zwitterion 1,5‐dipole equivalents and enol diazoacetates enables the formation of eight‐membered heterocyclic skeletons, which are otherwise difficult to construct. The optimized cycloaddition occurs efficiently under mild conditions with a wide range of pyridinium zwitterions and with high functional‐group tolerance. 相似文献
995.
Youngmin Ko Hyunji Park Kyunam Lee Dr. Sung Joo Kim Dr. Hyeokjun Park Dr. Youngjoon Bae Jihyeon Kim Prof. Soo Young Park Dr. Ji Eon Kwon Prof. Kisuk Kang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(13):5414-5418
Redox mediators (RMs) are considered an effective countermeasure to reduce the large polarization in lithium-oxygen batteries. Nevertheless, achieving sufficient enhancement of the cyclability is limited by the trade-offs of freely mobile RMs, which are beneficial for charge transport but also trigger the shuttling phenomenon. Here, we successfully decoupled the charge-carrying redox property of RMs and shuttling phenomenon by anchoring the RMs in polymer form, where physical RM migration was replaced by charge transfer along polymer chains. Using PTMA (poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate)) as a polymer model system based on the well-known RM tetramethylpiperidinyloxyl (TEMPO), it is demonstrated that PTMA can function as stationary RM, preserving the redox activity of TEMPO. The efficiency of RM-mediated Li2O2 decomposition remains remarkably stable without the consumption of oxidized RMs or degradation of the lithium anode, resulting in an improved performance of the lithium-oxygen cell. 相似文献
996.
Tereza Košutová Lukáš Horák Artem Shelemin Mykhailo Vaidulych Jan Hanuš Hynek Biederman Ondřej Kylián Pavel Solař Miroslav Cieslar Andrei Choukourov Milan Dopita 《Surface and interface analysis : SIA》2020,52(12):1023-1028
Metal-polymer nanocomposites have gained increasing attention due to the wide potential applications field. Synthesis of nanoparticles from the gas phase is an intensively studied alternative to the chemical preparation methods. We present a one-step procedure that combines magnetron-based gas aggregation cluster source of silver nanoparticles and simultaneous plasma-enhanced chemical vapour deposition of hexamethyldisiloxane (HMDSO). The key parameter of the process, significantly influencing the morphology and microstructure of studied nanoparticles, was found to be the amount of HMDSO added to the deposition chamber as witnessed by small angle X-ray scattering and X-ray diffraction methods combined with transmission electron microscopy and UV–Vis spectrophotometry. The presence of HMDSO in the chamber leads to changes in the size distribution and also in the architecture of prepared nanoparticles. The increasing amount of HMDSO induces the formation of individual core-shell nanoparticles, chains of core-shell nanoparticles, and for the highest concentration of HMDSO, the synthesis of multi-core-shell nanoparticles. The size of crystallites in the silver cores of nanoparticles decreases with addition of HMDSO, which prevents further aggregation. 相似文献
997.
We deal with the D-dimensional radial Klein-Gordon equation for Rosen-Morse type potential with unequal scalar and vector potentials. We apply a proper approximation to the centrifugal term and, by proposing an ansatz solution to the resulting equation, we obtain the bound-state solution. To check the accuracy of our results, we compare our obtained quasi-analytical energies with the exact numerical ones. 相似文献
998.
Tae-Yeon Cho Kwan-Woo Ko Soon-Gil Yoon Satpal Singh Sekhon Man Gu Kang Young-Sik Hong Chi-Hwan Han 《Current Applied Physics》2013,13(7):1391-1396
We investigated the effect of a Nb2O5 blocking layer formed through the sol–gel method introduced to a titanium metal foil electrode in a flexible dye sensitized solar cell. The blocking layer formed directly on the working electrode physically separates the working electrode from the electrolyte, and prevents back transfer of electrons from the electrode to the electrolyte. The gel processing conditions (sol reaction time) and heat treatment temperature used in formation of the Nb2O5 blocking layer have been shown to affect the performance of the dye sensitized solar cell and optimal values of these parameters have been determined. A sol reaction time of 45 min and heat treatment temperature of 550 °C has been observed to result in optimal cell performance (η = 6.185%, Jsc = 13.233 mA/cm2, Voc = 0.672 V, ff = 0.694). Introduction of an Nb2O5 blocking layer enhances solar cell efficiency by 39.7%, which is much greater than the increase of 24.6% observed in a similar cell containing a TiO2 blocking layer under standard illumination conditions. The results obtained via Nb2O5 have been observed to be superior to those obtained via a TiO2 blocking layer. 相似文献
999.
Min-Seok Jeong Jae Hyun Kim Jae-Hyeon Ko Young Ho Ko Kwang Joo Kim 《Current Applied Physics》2013,13(8):1774-1777
The pressure dependences of the longitudinal sound velocity and the refractive index of amorphous Kel F-800 copolymer were investigated for pressures up to 13 GPa using high-pressure Brillouin spectroscopy combined with a diamond-anvil-cell technique. The sound velocity increased rapidly with increasing pressure at pressures below ~2 GPa, whereas it showed a mild change at higher pressure values. This was attributed to substantial collapse of effective free volume in this amorphous material. The refractive index could be measured by comparing the Brillouin spectra measured from backward and forward, symmetric scattering geometries. The pressure–density relationship could be obtained by using Lorentz–Lorenz equation based on an assumption of constant polarizability, which was consistent with that reported by previous study. 相似文献
1000.
Two amino acid derived synthons were combined to give homopropargylic amines 2. Platinum dichloride was used to cyclize these intermediates into pyrroles 3 which collapsed to the target secondary structure mimics 1 on treatment with base. Side chains of these compounds overlay with an idealized type 1 β-turn and with an inverse γ-turn. 相似文献