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941.
Aryl‐Copper(III)‐Acetylides as Key Intermediates in CCsp Model Couplings under Mild Conditions 下载免费PDF全文
Mireia Rovira Marc Font Ferran Acuña‐Parés Dr. Teodor Parella Dr. Josep M. Luis Dr. Julio Lloret‐Fillol Dr. Xavi Ribas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):10005-10010
The mechanism of copper‐mediated Sonogashira couplings (so‐called Stephens–Castro and Miura couplings) is not well understood and lacks clear comprehension. In this work, the reactivity of a well‐defined aryl‐CuIII species ( 1 ) with p‐R‐phenylacetylenes (R=NO2, CF3, H) is reported and it is found that facile reductive elimination from a putative aryl‐CuIII‐acetylide species occurs at room temperature to afford the Caryl?Csp coupling species ( IR ), which in turn undergo an intramolecular reorganisation to afford final heterocyclic products containing 2H‐isoindole ( P , P , PHa ) or 1,2‐dihydroisoquinoline ( PHb ) substructures. Density Functional Theory (DFT) studies support the postulated reductive elimination pathway that leads to the formation of C?Csp bonds and provide the clue to understand the divergent intramolecular reorganisation when p‐H‐phenylacetylene is used. Mechanistic insights and the very mild experimental conditions to effect Caryl?Csp coupling in these model systems provide important insights for developing milder copper‐catalysed Caryl?Csp coupling reactions with standard substrates in the future. 相似文献
942.
Transalkylation of Higher Trifluoromethylated Fullerenes with C70: A Pathway to New Addition Patterns of C70(CF3)8 下载免费PDF全文
Nikita M. Belov Marina G. Apenova Alexey V. Rybalchenko Eugenia V. Borkovskaya Dr. Natalia S. Lukonina Dr. Alexey A. Goryunkov Dr. Ilya N. Ioffe Prof. Dr. Sergey I. Troyanov Prof. Dr. Lev N. Sidorov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(4):1126-1133
We report three new isomers of C70(CF3)8, structurally related to p7mp‐C70(CF3)10, that are inaccessible by direct trifluoromethylation, but can be easily identified among the products of the transalkylation of higher trifluoromethylfullerenes with C70. The reported compounds are characterized by UV/Vis, 1 D and 2 D COSY 19F NMR spectroscopy, and DFT calculations. A rather unusual addition pattern is observed in p6,i‐C70(CF3)8 in which one addend is attached remotely from the others; polarization of the adjacent unsaturated bonds by the addend makes the molecule readily oxidizable. 相似文献
943.
Brandon Z. Child Dr. Santanab Giri Dr. Scott Gronert Dr. Puru Jena 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(16):4736-4745
No organic molecules with electron affinities near or above those of halogens are known. We show for the first time that aromaticity rules can be used to design molecules with electron affinities far exceeding those of halogen atoms either by tailoring the ligands of cyclopentadienyl or by multiple benzoannulations of cyclopentadienyl in conjunction with the substitution of CH groups with isoelectronic N atoms. Results based on density functional theory revealed that the electron affinities of some of these organic molecules can reach as high as 5.59 eV, thus opening the door to new class of superhalogens that contain neither a metal nor a halogen atom. 相似文献
944.
945.
Phase‐Transfer‐Catalysed Synthesis of Pyrroloindolines and Pyridoindolines by a Hydrogen‐Bond‐Assisted Isocyanide Cyclization Cascade 下载免费PDF全文
Dr. Peter C. Knipe Dr. Matija Gredičak Artiom Cernijenko Dr. Robert S. Paton Dr. Martin D. Smith 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(11):3005-3009
A cascade reaction that generates pyrrolo‐ and pyridoindoline motifs from isocyanide precursors under phase‐transfer conditions is described. This transformation proceeds at room temperature in the presence of a quaternary ammonium catalyst and base to generate functionalized products containing an all‐carbon quaternary stereocentre. Quantum chemical calculations demonstrated that intramolecular general acid catalysis plays a key accelerating role through stabilization of developing charge in the transition state, and that the reaction is best described as a 5‐endo dig cyclization, rather than an anionic 6π electrocyclization. Investigations employing chiral phase‐transfer catalysts have given promising selectivities to date. 相似文献
946.
Dr. Martín Regueiro‐Figueroa Dr. David Esteban‐Gómez Dr. Andrés de Blas Dr. Teresa Rodríguez‐Blas Dr. Carlos Platas‐Iglesias 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3974-3981
The stability trends across the lanthanide series of complexes with the polyaminocarboxylate ligands TETA4? (H4TETA=2,2′,2′′,2′′′‐(1,4,8,11‐tetraazacyclotetradecane‐1,4,8,11‐tetrayl)tetraacetic acid), BCAED4? (H4BCAED=2,2′,2′′,2′′′‐{[(1,4‐diazepane‐1,4‐diyl)bis(ethane‐2,1‐diyl)]bis(azanetriyl)}tetraacetic acid), and BP18C62? (H2BP18C6=6,6′‐[(1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane‐7,16‐diyl)bis(methylene)]dipicolinic acid) were investigated using DFT calculations. Geometry optimizations performed at the TPSSh/6‐31G(d,p) level, and using a 46+4fn ECP for lanthanides, provide bond lengths of the metal coordination environments in good agreement with the experimental values observed in the X‐ray structures. The contractions of the Ln3+ coordination spheres follow quadratic trends, as observed previously for different isostructural series of complexes. We show here that the parameters obtained from the quantitative analysis of these data can be used to rationalize the observed stability trends across the 4f period. The stability trends along the lanthanide series were also evaluated by calculating the free energy for the reaction [La( L )]n+/?(sol)+Ln3+(sol)→[Ln( L )]n+/?(sol)+La3+(sol). A parameterization of the Ln3+ radii was performed by minimizing the differences between experimental and calculated standard hydration free energies. The calculated stability trends are in good agreement with the experimental stability constants, which increase markedly across the series for BCAED4? complexes, increase smoothly for the TETA4? analogues, and decrease in the case of BP18C62? complexes. The resulting stability trend is the result of a subtle balance between the increased binding energies of the ligand across the lanthanide series, which contribute to an increasing complex stability, and the increase in the absolute values of hydration energies along the 4f period. 相似文献
947.
S=1/2 One‐Dimensional Random‐Exchange Ferromagnetic Zigzag Ladder,Which Exhibits Competing Interactions in a Critical Regime 下载免费PDF全文
Susan N. Herringer Dr. Mercè Deumal Dr. Jordi Ribas‐Arino Prof. Juan J. Novoa Prof. Christopher P. Landee Prof. Jan L. Wikaira Prof. Mark M. Turnbull 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(27):8355-8362
The synthesis, crystal structure, and magnetic properties (from a combined experimental and First‐Principles Bottom‐Up theoretical study) of the new compound catena‐dichloro(2‐Cl‐3Mpy)copper(II), 1 , [2‐Cl‐3Mpy=2‐chloro‐3‐methylpyridine] are described and rationalized. Crystals of 1 present well isolated magnetic 1D chains (no 3D order was experimentally observed down to 1.8 K) and magnetic frustration stemming from competing ferromagnetic nearest‐neighbor (JNN) interactions and antiferromagnetic next‐nearest neighbor (JNNN) interactions, in which α=JNNN/JNN <?0.25. These magnetic interactions give rise to a unique magnetic topology: a two‐leg zigzag ladder composed of edge‐sharing up‐down triangles with antiferromagnetic interactions along the rails and ferromagnetic interactions along the zigzag chain that connects the rails. Crystals of 1 also present a random distribution of the 2‐Cl‐3Mpy groups, which are arranged in two different orientations, each with a 50 % occupancy. This translates into a random static structural disorder within each chain by virtue of which the value of the JNN magnetic interactions can randomly take one of the following three values: 53, 36, and 16 cm?1. The structural disorder does not affect the JNNN value, which in all cases is approximately ?9 cm?1. A proper statistical treatment of this disorder provides a computed magnetic susceptibility curve that reproduces the main features of the experimental data. 相似文献
948.
Highly Enantioselective Extraction of Underivatized Amino Acids by the Uryl‐Pendant Hydroxyphenyl‐Binol Ketone 下载免费PDF全文
Dr. Haofei Huang Qian Chen Misun Choi Prof. Raju Nandhakumar Dr. Zhishan Su Prof. Dr. Sihyun Ham Prof. Kwan Mook Kim 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(10):2895-2900
The hydroxyphenyl chiral ketone, (S)‐ 3 , reacts with D ‐amino acids bearing hydrophobic side chains exclusively over the L ‐amino acids in a two‐phase liquid–liquid extraction, and thus acts as a highly stereoselective extractant. Calculations for the energy‐minimized structures for the imine diastereomers and the comparison of the selectivities with other phenyl ketones, (S)‐ 4 and (S)‐ 5 , demonstrate that the hydrogen bond between the carboxylate group and the phenolic hydroxyl group contributes to the remarkable enantioselectivities. The multiple hydrogen bonds present in the imine of (S)‐ 3 reinforce the rigidity, and results in the difference between the stabilities of the imine diastereomers. The imine could be hydrolyzed in methanolic HCl solution, and the extraction of the evaporated residues revived the organic layer of (S)‐ 3 , which could enter into a new extractive cycle and leaves the D ‐amino acid with enantiomeric excess (ee) values of over 97 % in the aqueous layer. 相似文献
949.
Thermal Ethane Activation by Bare [V2O5]+ and [Nb2O5]+ Cluster Cations: on the Origin of Their Different Reactivities 下载免费PDF全文
Dr. Xiao‐Nan Wu Dr. Shi‐Ya Tang Dr. Hai‐Tao Zhao Dr. Thomas Weiske Dr. Maria Schlangen Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(22):6672-6677
The gas‐phase reactivity of [V2O5]+ and [Nb2O5]+ towards ethane has been investigated by means of mass spectrometry and density functional theory (DFT) calculations. The two metal oxides give rise to the formation of quite different reaction products; for example, the direct room‐temperature conversions C2H6→C2H5OH or C2H6→CH3CHO are brought about solely by [V2O5]+. In distinct contrast, for the couple [Nb2O5]+/C2H6, one observes only single and double hydrogen‐atom abstraction from the hydrocarbon. DFT calculations reveal that different modes of attack in the initial phase of C?H bond activation together with quite different bond‐dissociation energies of the M?O bonds cause the rather varying reactivities of [V2O5]+ and [Nb2O5]+ towards ethane. The gas‐phase generation of acetaldehyde from ethane by bare [V2O5]+ may provide mechanistic insight in the related vanadium‐catalyzed large‐scale process. 相似文献
950.
石墨烯条带的电子结构与性质:电场及长度效应 总被引:1,自引:0,他引:1
在密度泛函理论(DFT)和含时密度泛函理论(TDDFT)的基础上对宽度上含有8个zigzag链的石墨烯条带(8-ZGNR)的基态和激发态的性质进行了理论研究,着重考察了条带长度及电场的影响.B3LYP杂化泛函的计算结果显示:在基态上,8-ZGNR的最低能量态并不具有磁性,随着长度的增加,才会显示出反铁磁的性质.静电场的加入使8-ZGNR显示出反铁磁性和半金属性.在激发态上,诱导电子会随着外激光脉冲的变化而发生移动和变化,但是相比而言,α自旋电子更容易被激发而产生较明显的诱导电子密度,而β自旋电子则更容易脱离外激光场的控制而产生非绝热现象. 相似文献