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981.
An Independent 1D Single‐Walled Metal–Organic Nanotube Transformed from a 2D Layer Exhibits Highly Selective and Reversible Sensing of Nitroaromatic Compounds 下载免费PDF全文
Prof. Dr. Qingfu Zhang Aijing Geng Haina Zhang Falu Hu Prof. Dr. Zhang‐Hui Lu Prof. Dr. Dezhi Sun Prof. Xilian Wei Prof. Dr. Chunlin Ma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4885-4890
The syntheses and structures of two new ZnII complexes, a 2D graphite‐like layer {[Zn(PIA)H2O] ? H2O}n ( 1 ) and an independent 1D single‐walled metal–organic nanotube (SWMONT) {[Zn2(PIA)2(bpy)2] ? 2.5 H2O ? DMA}n ( 2 ), have been reported based on a “Y”‐shaped 5‐(pyridine‐4‐yl)isophthalic acid ligand (H2PIA). Interestingly, the 2D graphite‐like layer in 1 can transform into the independent 1D SWMONT in 2 with addition of 2,2′‐bipyridine (bpy), which represents the first successfully experimental example of an independent 1D metal–organic nanotube generated from a 2D layer by a “rolling‐up” mechanism. 相似文献
982.
Frank Meyer‐Wegner Josef H. Wender Konstantin Falahati Timo Porsch Tanja Sinke Dr. Michael Bolte Prof. Dr. Matthias Wagner Prof. Dr. Max C. Holthausen Dr. Hans‐Wolfram Lerner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4681-4690
The reaction of 4‐chloro‐1,2‐dimethyl‐4‐supersilylsila‐1‐cyclopentene ( 2 a ) with Li[NiPr2] at ?78 °C results in the formation of the formal 1,4‐addition product of the silacyclopentadiene derivative 3,4‐dimethyl‐1‐supersilylsila‐1,3‐cyclopentadiene ( 4 a ) with 2,3‐dimethyl‐4‐supersilylsila‐1,3‐cyclopentadiene ( 5 a ). In addition the respective adducts of the Diels–Alder reactions of 4 a + 4 a and 4 a + 5 a were obtained. Compound 4 a , which displays an s‐cis‐silacyclopentadiene configuration, reacts with cyclohexene to form the racemate of the [4+2] cycloadduct of 4 a and cyclohexene ( 9 ). In the reaction between 4 a and 2,3‐dimethylbutadiene, however, 4 a acted as silene as well as silacyclopentadiene to yield the [2+4] and [4+2] cycloadducts 10 and 11 , respectively. The constitutions of 9 , 10 , and 11 were confirmed by NMR spectroscopy and their crystal structures were determined. Reaction of 4‐chloro‐1,2‐dimethyl‐4‐tert‐butyl‐4‐silacyclopent‐1‐ene ( 2 c ) with KC8 yielded the corresponding disilane ( 12 ), which was characterized by X‐ray crystal structure analysis (triclinic, P$\bar 1$ ). DFT calculations are used to unveil the mechanistic scenario underlying the observed reactivity. 相似文献
983.
Ruthenium(II)‐Catalyzed Synthesis of Isochromenes by CH Activation with Weakly Coordinating Aliphatic Hydroxyl Groups 下载免费PDF全文
Sachiyo Nakanowatari Prof. Dr. Lutz Ackermann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(18):5409-5413
Cationic ruthenium(II) complexes have been employed for the highly effective oxidative annulation of alkynes with benzyl alcohols to deliver diversely decorated isochromenes. The hydroxyl‐directed C?H/O?H functionalization process proceeded efficiently under an atmosphere of air. Detailed mechanistic studies were indicative of a kinetically relevant C?H metalation. 相似文献
984.
Dynamics of the NbCl5‐Catalyzed Cycloaddition of Propylene Oxide and CO2: Assessing the Dual Role of the Nucleophilic Co‐Catalysts 下载免费PDF全文
Dr. Valerio D'Elia Dr. Amylia A. Ghani Dr. Antoine Monassier Dr. Julien Sofack‐Kreutzer Dr. Jeremie D. A. Pelletier Dr. Markus Drees Dr. Sai V. C. Vummaleti Dr. Albert Poater Prof. Dr. Luigi Cavallo Dr. Mirza Cokoja Prof. Dr. Jean‐Marie Basset Prof. Dr. Fritz. E. Kühn 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(37):11870-11882
A mechanistic study on the synthesis of propylene carbonate (PC) from CO2 and propylene oxide (PO) catalyzed by NbCl5 and organic nucleophiles such as 4‐dimethylaminopyridine (DMAP) or tetra‐n‐butylammonium bromide (NBu4Br) is reported. A combination of in situ spectroscopic techniques and kinetic studies has been used to provide detailed insight into the reaction mechanism, the formation of intermediates, and interactions between the reaction partners. The results of DFT calculations support the experimental observations and allow us to propose a mechanism for this reaction. 相似文献
985.
Understanding Bacterial Bioluminescence: A Theoretical Study of the Entire Process,from Reduced Flavin to Light Emission 下载免费PDF全文
Cong Hou Prof. Dr. Ya‐Jun Liu Prof. Dr. Nicolas Ferré Prof. Dr. Wei‐Hai Fang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(26):7979-7986
Bacterial bioluminescence (BL) has been successfully applied in water‐quality monitoring and in vivo imaging. The attention of researchers has been attracted for several decades, but the mechanism of bacterial BL is still largely unknown due to the complexity of the multistep reaction process. Debates mainly focus on three key questions: How is the bioluminophore produced? What is the exact chemical form of the bioluminophore? How does the protein environment affect the light emission? Using quantum mechanics (QM), combined QM and molecular mechanics (QM/MM) and molecular dynamic (MD) calculations in gas‐phase, solvent and protein environments, the entire process of bacterial BL was investigated, from flavin reduction to light emission. This investigation revealed that: 1) the chemiluminescent decomposition of flavin peroxyhemiacetal does not occur through the intramolecular chemical initiated electron exchange luminescence (CIEEL) or the “dioxirane” mechanism, as suggested in the literature. Instead, the decomposition occurs according to the charge‐transfer initiated luminescence (CTIL) mechanism for the thermolysis of dioxetanone. 2) The first excited state of 4a‐hydroxy‐4a,5‐dihydroFMN (HFOH) was affirmed to be the bioluminophore of bacterial BL. This study provides details regarding the mechanism by which bacterial BL is produced and is helpful in understanding bacterial BL in general. 相似文献
986.
Hydrogen Release from Dialkylamine–Boranes Promoted by Mg and Ca Complexes: A DFT Analysis of the Reaction Mechanism 下载免费PDF全文
Dr. Valeria Butera Prof. Nino Russo Prof. Dr. Emilia Sicilia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):5967-5976
Mg and Ca β‐diketiminato silylamides [HC{(Me)CN(2,6‐iPr2C6H3)}2M(THF)n{N(SiMe3)2}] (M=Mg, n=0; M=Ca, n=1) were studied as precatalysts for the dehydrogenation/dehydrocoupling of secondary amine–boranes R2HNBH3. By reaction with equimolar quantities of amine–boranes, the corresponding amidoborane derivatives are formed, which further react to yield dehydrogenation products such as the cyclic dimer [BH2?NMe2]2. DFT was used here to explore the mechanistic alternatives proposed on the basis of the experimental findings for both Mg and Ca amidoboranes. The influence of the steric demand of amine–boranes on the course of the reaction was examined by performing calculations on the dehydrogenation of dimethylamine–borane (DMAB), pyrrolidine–borane (PB), and diisopropylamine–borane. In spite of the analogies in the catalytic activity of Mg‐ and Ca‐based complexes in the dehydrocoupling of amine–boranes, our theoretical analysis confirmed the experimentally observed lower reactivity of Ca complexes. Differences in catalytic activity of Mg‐ and Ca‐based complexes were examined and rationalized. As a consequence of the increase in ionic radius on going from Mg2+ to Ca2+, the dehydrogenation mechanism changes and formation of a key metal hydride intermediate becomes inaccessible. Dimerization is likely to occur off‐metal in solution for DMAB and PB, whereas steric hindrance of iPr2NHBH3 hampers formation of the cyclic dimer. The reported results are of particular interest because, although amine–borane dehydrogenation is now well established, mechanistic insight is still lacking for many systems. 相似文献
987.
Cationic Copper(I) Complexes as Highly Efficient Catalysts for Single and Double A3‐Coupling Mannich Reactions of Terminal Alkynes: Mechanistic Insights and Comparative Studies with Analogous Gold(I) Complexes 下载免费PDF全文
Dr. Abdessamad Grirrane Dr. Eleuterio Álvarez Prof. Hermenegildo García Prof. Avelino Corma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14317-14328
Cationic Cu?L complexes (L=Buchwald‐type phosphane) with N co‐ligands have been characterised by structural and spectroscopic properties. These copper(I) complexes are extremely active catalysts, far more active than analogous gold(I) complexes, to promote the single and double A3 coupling of terminal alkynes, pyrrolidine and formaldehyde. The activity data show the possible ways in which the solvent can influence the catalytic performance by limiting complex solubility, by solvent decomposition or instability of the copper(I) redox state. Isolation of copper(I) complexes that are likely to be the key catalytic species has allowed light to be shed on the reaction mechanism. 相似文献
988.
Liquid chromatographic behavior of two alanine‐substituted calix[4]arene‐bonded silica gel stationary phases 下载免费PDF全文
Zhifen Deng Junwei Liu Chenchen Hu Liu Yang Huifang Du Yanjie Huang Xiaoqing Yang Qiong Jiang Shusheng Zhang 《Journal of separation science》2014,37(22):3268-3275
Two new kinds of alanine‐substituted calix[4]arene stationary phases of 5,11,17,23‐p‐tert‐butyl‐25,27‐bis(l ‐alanine‐methylester‐N‐carbonyl‐methoxy)‐26,28‐dihyroxycalix[4]arene‐bonded silica gel stationary phase (BABS4) and 5, 11, 17, 23‐p‐tert‐butyl‐25,26,27,28‐tetra(l ‐alanine‐methylester‐N‐carbonyl‐methoxy)‐calix[4]arene‐bonded silica gel stationary phase (TABS4) were prepared and characterized in the present study. They were compared with each other and investigated in terms of their chromatographic performance by using polycyclic aromatic hydrocarbons, disubstituted benzene isomers, and mono‐substituted benzenes as solute probes. The results indicated that both BABS4 and TABS4 exhibited multiple interactions with analytes. In addition, the commonly used Tanaka characterization protocol for the evaluation of commercially available stationary phases was applied to evaluate the properties of these two new functionalized calixarene stationary phases. The Tanaka test results were compared with Zorbax Eclipse XDB C18 and Kromasil phenyl columns, respectively. BABS4 has stronger hydrogen‐bonding capacity and ion‐exchange capacity than TABS4, and features weaker hydrophobicity and hydrophobic selectivity. Both of them behave similarly in stereoselectivity. Both BABS4 and TABS4 are weaker than C18 and phenyl stationary phases in hydrophobicity and hydrophobic selectivity. 相似文献
989.
Computational studies, especially those that use density functional theory (DFT), have become pervasive in the characterization, mechanistic study, and optimization of homogeneous organometallic catalysts, and the “rational” design of such catalysts seems within reach once more. But how advanced, user‐friendly, and reliable are the computational tools that are currently available? Here we summarize the current state of the art for predictive computational organometallic chemistry in reference to the different stages of catalyst development by considering characterization, mechanistic studies, fine‐tuning/optimization, and evaluation of novel designs. We also assess critically where the strengths and weaknesses of computational studies lie and hence map out the road ahead for the design and discovery of novel catalysts in silico and in combination with targeted experimental studies. 相似文献
990.
Diels–Alder Reaction on Free C68 Fullerene and Endohedral Sc3N@C68 Fullerene Violating the Isolated Pentagon Rule: Importance of Pentagon Adjacency 下载免费PDF全文
Dr. Tao Yang Prof. Dr. Xiang Zhao Prof. Dr. Shigeru Nagase Prof. Dr. Takeshi Akasaka 《化学:亚洲杂志》2014,9(9):2604-2611
The reaction mechanism and regioselectivity of the Diels–Alder reactions of C68 and Sc3N@C68, which violate the isolated pentagon rule, were studied with density functional theory calculations. For C68, the [5,5] bond is the most favored thermodynamically, whereas the cycloaddition on the [5,6] bond has the lowest activation energy. Upon encapsulation of the metallic cluster, the exohedral reactivity of Sc3N@C68 is reduced remarkably owing to charge transfer from the cluster to the fullerene cage. The [5,5] bond becomes the most reactive site thermodynamically and kinetically. The bonds around the pentagon adjacency show the highest chemical reactivity, which demonstrates the importance of pentagon adjacency. Furthermore, the viability of Diels–Alder cycloadditions of several dienes and Sc3N@C68 was examined theoretically. o‐Quinodimethane is predicted to react with Sc3N@C68 easily, which implies the possibility of using Diels–Alder cycloaddition to functionalize Sc3N@C68. 相似文献