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961.
M. Sc. Keshav Raghuvanshi Karsten Rauch Prof. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1790-1794
Intermolecular C?H acyloxylations of phenols with removable directing groups were accomplished with a versatile ruthenium catalyst. Specifically, a cationic ruthenium(II) complex, formed in situ, enabled the chemoselective C?H oxygenations of a broad range of substrates. The catalyst proved tolerant of synthetically valuable functional groups, and the substrate scope included both (hetero)aromatic and, the more challenging, aliphatic carboxylic acids. The proposed reaction mechanism involves a reversible C?H ruthenation and an oxidatively induced C?O‐bond‐forming reductive elimination. 相似文献
962.
Experimental and Computational Studies on the CH Amination Mechanism of Tetrahydrocarbazoles via Hydroperoxides 下载免费PDF全文
Dr. Naeem Gulzar Dr. Kevin Mark Jones Hannelore Konnerth Dr. Martin Breugst Dr. Martin Klussmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3367-3376
The acid‐catalyzed reactions of photochemically generated tetrahydrocarbazole peroxides with anilines have been studied experimentally and computationally to identify the underlying reaction mechanism. The kinetic data indicate a reaction order of one in the hydroperoxide and zero in the aniline. Computational investigations using density functional theory support the experimental findings and predict an initial tautomerization between an imine and enamine substructure of the primarily generated tetrahydrocarbazole peroxide to be the rate controlling step. The enamine tautomer then loses hydrogen peroxide upon protonation, generating a stabilized allylic carbocation that is reversibly trapped by solvent or aniline to form the isolated products. 相似文献
963.
Insight into the Mechanism of Hydrogenation of Amino Acids to Amino Alcohols Catalyzed by a Heterogeneous MoOx‐Modified Rh Catalyst 下载免费PDF全文
Dr. Masazumi Tamura Riku Tamura Yasuyuki Takeda Dr. Yoshinao Nakagawa Prof. Keiichi Tomishige 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):3097-3107
Hydrogenation of amino acids to amino alcohols is a promising utilization of natural amino acids. We found that MoOx‐modified Rh/SiO2 (Rh–MoOx/SiO2) is an efficient heterogeneous catalyst for the reaction at low temperature (323 K) and the addition of a small amount of MoOx drastically increases the activity and selectivity. Here, we report the catalytic potential of Rh–MoOx/SiO2 and the results of kinetic and spectroscopic studies to elucidate the reaction mechanism of Rh–MoOx/SiO2 catalyzed hydrogenation of amino acids to amino alcohols. Rh–MoOx/SiO2 is superior to previously reported catalysts in terms of activity and substrate scope. This reaction proceeds by direct formation of an aldehyde intermediate from the carboxylic acid moiety, which is different from the reported reaction mechanism. This mechanism can be attributed to the reactive hydride species and substrate adsorption caused by MoOx modification of Rh metal, which results in high activity, selectivity, and enantioselectivity. 相似文献
964.
Nanostructured Ni2P as a Robust Catalyst for the Hydrolytic Dehydrogenation of Ammonia–Borane 下载免费PDF全文
Cheng‐Yun Peng Lei Kang Shuang Cao Prof. Dr. Yong Chen Prof. Dr. Zhe‐Shuai Lin Prof. Dr. Wen‐Fu Fu 《Angewandte Chemie (International ed. in English)》2015,54(52):15725-15729
Ammonia–borane (AB) is a promising chemical hydrogen‐storage material. However, the development of real‐time, efficient, controllable, and safe methods for hydrogen release under mild conditions is a challenge in the large‐scale use of hydrogen as a long‐term solution for future energy security. A new class of low‐cost catalytic system is presented that uses nanostructured Ni2P as catalyst, which exhibits excellent catalytic activity and high sustainability toward hydrolysis of ammonia–borane with the initial turnover frequency of 40.4 mol(H2) mol(Ni2P)?1 min?1 under air atmosphere and at ambient temperature. This value is higher than those reported for noble‐metal‐free catalysts, and the obtained Arrhenius activation energy (Ea=44.6 kJ mol?1) for the hydrolysis reaction is comparable to Ru‐based bimetallic catalysts. A clearly mechanistic analysis of the hydrolytic reaction of AB based on experimental results and a density functional theory calculation is presented. 相似文献
965.
Wide‐angle X‐ray scattering study of the lamellar/fibrillar transition for a semi‐crystalline polymer deformed in tension in relation with the evolution of volume strain 下载免费PDF全文
Laurent Farge Julien Boisse Jérôme Dillet Stéphane André Pierre‐Antoine Albouy Florian Meneau 《Journal of Polymer Science.Polymer Physics》2015,53(20):1470-1480
This work is devoted to the study of the deformation mechanisms of a high‐density polyethylene deformed in tension. Specific treatments were applied to synchrotron wide‐angle X‐ray scattering patterns obtained in situ with the aim of quantifying: (i) the evolution of the apparent crystal sizes during the deformation process, (ii) the reorientation dynamics of the fragmented crystals while aligning their chains along the drawing axis during the establishment of the fibrillar morphology, and (iii) the reorientation dynamics of the amorphous chains. In addition, the volume strain evolution was measured using 3D digital image correlation. The cavitation phenomenon was found to mainly occur during the lamellae fragmentation phase. At the end of the deformation process, when the lamellar structure is destroyed, the fragmented crystals have new degrees of freedom and become free to rotate to align their chains along the drawing axis. Crystal fragmentation is then no longer needed to allow material deformation, and there is no further volume strain increase. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1470–1480 相似文献
966.
颗粒物质混合行为的离散单元法研究 总被引:1,自引:0,他引:1
颗粒物质的混合是化学工业生产的重要单元操作,由于颗粒物质运动行为的复杂性,工业混合器中的颗粒运动规律及物理机制至今仍未被全面认识。作为一种精细的数值方法,离散单元法(discrete element method,DEM)在单颗粒尺度上描述颗粒物质的受力与运动行为,因此在研究混合机理方面具有独特优势。随着DEM模型与计算技术的快速发展,DEM已被广泛应用于各种混合过程的研究。通过DEM可以全面考察不同的颗粒性质、混合器类型以及操作条件等因素对混合机理的影响,从而对于指导粉体工业的生产操作及设备优化改进具有重要意义。本文重点阐述了DEM在无黏颗粒、黏结性颗粒、非球形颗粒混合过程模拟以及大规模计算等方面的最新进展,并对未来发展进行了展望。 相似文献
967.
Iridium‐Catalyzed Reductive Carbon–Carbon Bond Cleavage Reaction on a Curved Pyridylcorannulene Skeleton 下载免费PDF全文
Dr. Shohei Tashiro Dr. Mihoko Yamada Prof. Dr. Mitsuhiko Shionoya 《Angewandte Chemie (International ed. in English)》2015,54(18):5351-5354
The cleavage of C? C bonds in π‐conjugated systems is an important method for controlling their shape and coplanarity. An efficient way for the cleavage of an aromatic C? C bond in a typical buckybowl corannulene skeleton is reported. The reaction of 2‐pyridylcorannulene with a catalytic amount of IrCl3?n H2O in ethylene glycol at 250 °C resulted in a structural transformation from the curved corannulene skeleton to a strain‐free flat benzo[ghi]fluoranthene skeleton through a site‐selective C? C cleavage reaction. This cleavage reaction was found to be driven by both the coordination of the 2‐pyridyl substituent to iridium and the relief of strain in the curved corannulene skeleton. This finding should facilitate the design of carbon nanomaterials based on C? C bond cleavage reactions. 相似文献
968.
Synthesis of a Stable Selenoaldehyde by Self‐Catalyzed Thermal Dehydration of a Primary‐Alkyl‐Substituted Selenenic Acid 下载免费PDF全文
Dr. Shohei Sase Ryo Kakimoto Prof. Dr. Kei Goto 《Angewandte Chemie (International ed. in English)》2015,54(3):901-904
The unprecedented dehydration of a selenenic acid (RCH2SeOH) to a selenoaldehyde (RCH?Se) has been demonstrated. A primary‐alkyl‐substituted selenenic acid was synthesized for the first time by taking advantage of a bulky cavity‐shaped substituent. Upon heating in solution, the selenenic acid underwent thermal dehydration to produce a stable selenoaldehyde, which was isolated as stable crystals and crystallographically characterized. Investigation of the reaction mechanism revealed that this β dehydration reaction involves two processes, both of which reflect the characteristics of a selenenic acid: 1) dehydrative condensation of two molecules of selenenic acid to generate a selenoseleninate intermediate [RCH2SeSe(O)CH2R], an isomer of a selenenic anhydride, and 2) subsequent β elimination of the selenenic acid from this intermediate to form a C?Se double bond, which establishes the self‐catalyzed β dehydration of the selenenic acid. 相似文献
969.
Pablo Morán‐Poladura Dr. Eduardo Rubio Prof. Dr. José M. González 《Angewandte Chemie (International ed. in English)》2015,54(10):3052-3055
The cycloisomerization reaction of 1‐(iodoethynyl)‐2‐(1‐methoxyalkyl)arenes and related 2‐alkyl‐substituted derivatives gives the corresponding 3‐iodo‐1‐substituted‐1H‐indene under the catalytic influence of IPrAuNTf2 [IPr=1,3‐bis(2,6‐diisopropyl)phenylimidazol‐2‐ylidene; NTf2=bis(trifluoromethanesulfonyl)imidate]. The reaction takes place in 1,2‐dichloroethane at 80 °C, and the addition of ttbp (2,4,6‐tri‐tert‐butylpyrimidine) is beneficial to accomplish this new transformation in high yield. The overall reaction implies initial assembly of an intermediate gold vinylidene upon alkyne activation by gold(I) and a 1,2‐iodine‐shift. Deuterium labeling and crossover experiments, the magnitude of the recorded kinetic primary isotopic effect, and the results obtained from the reaction of selected stereochemical probes strongly provide support for concerted insertion of the benzylic C? H bond into gold vinylidene as the step responsible for the formation of the new carbon–carbon bond. 相似文献
970.
Rhodium‐Catalyzed (5+1) Annulations Between 2‐Alkenylphenols and Allenes: A Practical Entry to 2,2‐Disubstituted 2H‐Chromenes 下载免费PDF全文
Noelia Casanova Andrés Seoane Prof. José L. Mascareñas Dr. Moisés Gulías 《Angewandte Chemie (International ed. in English)》2015,54(8):2374-2377
Readily available alkenylphenols react with allenes under rhodium catalysis to provide valuable 2,2‐disubstituted 2H‐chromenes. The whole process, which involves the cleavage of one C? H bond of the alkenyl moiety and the participation of the allene as a one‐carbon cycloaddition partner, can be considered a simple, versatile, and atom‐economical (5+1) heteroannulation. The reaction tolerates a broad range of substituents both in the alkenylphenol and in the allene, and most probably proceeds through a mechanism involving a rhodium‐catalyzed C? C coupling followed by two sequential pericyclic processes. 相似文献