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961.
Rocío Velasco Dr. Carlos Silva López Dr. Olalla Nieto Faza Prof. Dr. Roberto Sanz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(42):15058-15068
By carefully controlling the reaction temperature, treatment of aryl benzyl ethers with tBuLi selectively leads to α‐lithiation, generating stable organolithiums that can be directly trapped with a variety of selected electrophiles, before they can undergo the expected [1,2]‐Wittig rearrangement. This rearrangement has been deeply studied, both experimentally and computationally, with aryl α‐lithiated benzyl ethers bearing different substituents at the aryl ring. The obtained results support the competence of a concerted anionic intramolecular addition/elimination sequence and a radical dissociation/recombination sequence for explaining the tendency of migration for aryl groups. The more favored rearrangements are found for substrates with electron‐poor aryl groups that favor the anionic pathway. 相似文献
962.
Dr. Petr Jakubec Dr. Veronika Urbanová Dr. Zdenka Medříková Prof. Dr. Radek Zbořil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14279-14284
The sensing and accurate determination of antibiotics in various environments represents a big challenge, mainly owing to their widespread use in medicine, veterinary practice, and other fields. Therefore, a new, simple electrochemical sensor for the detection of antibiotic chloramphenicol (CAP) has been developed in this work. The amplification strategy of the sensor is based on the application of magnetite nanostructures stabilized with carboxymethyl cellulose (Fe3O4‐CMC) and decorated with nanometer‐sized Au nanoparticles (NPs) (Fe3O4‐CMC@Au). In this case, CMC serves as a stabilizing agent, preventing the aggregation of Fe3O4 NPs, and hence, enabling the kinetic barrier for electron transport to be overcome, and the Au NPs serve as an electron‐conducting tunnel for better electron transport. As a proof of concept, the developed nanosensor is used for the detection of CAP in human urine samples, giving a recovery value of around 97 %, which indicates the high accuracy of the as‐prepared nanosensor. 相似文献
963.
Dr. Heng Liao Dr. Liu Zhong Dr. Zefan Xiao Dr. Ting Zheng Prof. Haiyang Gao Prof. Qing Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):14048-14055
A series of novel α‐diamine nickel complexes, (ArNH‐C(Me)‐(Me)C‐NHAr)NiBr2, 1 : Ar=2,6‐diisopropylphenyl, 2 : Ar=2,6‐dimethylphenyl, 3 : Ar=phenyl), have been synthesized and characterized. X‐ray crystallographic analysis showed that the coordination geometry of the α‐diamine nickel complexes is markedly different from conventional α‐diimine nickel complexes, and that the chelate ring (N‐C‐C‐N‐Ni) of the α‐diamine nickel complex is significantly distorted. The α‐diamine nickel catalysts also display different steric effects on ethylene polymerization in comparison to the α‐diimine nickel catalyst. Increasing the steric hindrance of the α‐diamine ligand by substitution of the o‐methyl groups with o‐isopropyl groups leads to decreased polymerization activity and molecular weight; however, catalyst thermal stability is significantly enhanced. Living polymerizations of ethylene can be successfully achieved using 1 /Et2AlCl at 35 °C or 2 /Et2AlCl at 0 °C. The bulky α‐diamine nickel catalyst 1 with isopropyl substituents can additionally be used to control the branching topology of the obtained polyethylene at the same level of branching density by tuning the reaction temperature and ethylene pressure. 相似文献
964.
Dr. Brice Kauffmann Dr. Gilles Guichard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15684-15692
Anion binding properties of neutral helical foldamers consisting of urea type units in their backbone have been investigated. 1H NMR titration studies in various organic solvents including DMSO suggest that the interaction between aliphatic oligoureas and anions (CH3COO?, H2PO4?, Cl?) is site‐specific, as it largely involves the urea NHs located at the terminal end of the helix (positive pole of the helix), which do not participate to the helical intramolecular hydrogen‐bonding network. This mode of binding parallels that found in proteins in which anion‐binding sites are frequently found at the N‐terminus of an α‐helix. 1H NMR studies suggest that the helix of oligoureas remains largely folded upon anion binding, even in the presence of a large excess of the anion. This study points to potentially useful applications of oligourea helices for the selective recognition of small guest molecules. 相似文献
965.
Dr. Naoya Kumagai Prof. Dr. Masakatsu Shibasaki 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15192-15200
Recent advances in catalytic asymmetric carbon–carbon bond‐forming reactions of non‐heteroaromatic amide substrates are highlighted. Among carbonyl compounds, amides have received limited attention in catalytic asymmetric transformations mainly owing to their lower reactivity. Amides are reluctant to form enolates for nucleophilic addition, and α,β‐unsaturated amides exhibit diminished electrophilicity at the β‐carbon. Recent advances in asymmetric catalysis rendered these amides amenable to enantioselective reactions with perfect atom economy, producing synthetically useful chiral building blocks. This Minireview summarizes recent developments in the field. 相似文献
966.
Masashi Uebe Prof. Dr. Tatsuhisa Kato Prof. Dr. Kazuyoshi Tanaka Dr. Akihiro Ito 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18923-18931
The electronic and molecular structures of 9,10‐diamino‐substituted anthracenes with different N‐substituents have been re‐examined. In particular, different N‐substituents influence both the electronic and molecular structures of the oxidized species of 9,10‐diaminoanthracenes. The anthrylene moiety of 9,10‐bis(N,N‐di(p‐anisyl)amino)anthracene retains its planarity during the course of two successive one‐electron oxidations, whereas 9,10‐bis(N,N‐dimethylamino)anthracene and 9,10‐bis(N‐p‐anisyl‐N‐methylamino)anthracene undergo a substantial structural change to a butterfly‐like structure through a two‐electron oxidation process. The structural changes observed for the oxidized states are ascribed to significant differences in the frontier molecular orbitals of the above‐mentioned three kinds of 9,10‐diaminoanthracenes due to different extents of mixing between the amine‐localized and anthrylene‐localized orbitals. 相似文献
967.
Dr. Alexander R. Nödling Robert Möckel Dr. Ralf Tonner Prof. Dr. Gerhard Hilt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(37):13171-13180
The effect of several Lewis acids on the CBS catalyst (named after Corey, Bakshi and Shibata) was investigated in this study. While 2H NMR spectroscopic measurements served as gauge for the activation capability of the Lewis acids, in situ FT‐IR spectroscopy was employed to assess the catalytic activity of the Lewis acid oxazaborolidine complexes. A correlation was found between the Δδ(2H) values and rate constants kDA, which indicates a direct translation of Lewis acidity into reactivity of the Lewis acid–CBS complexes. Unexpectedly, a significant deviation was found for SnCl4 as Lewis acid. The SnCl4–CBS adduct was much more reactive than the Δδ(2H) values predicted and gave similar reaction rates to those observed for the prominent AlBr3–CBS adduct. To rationalize these results, quantum mechanical calculations were performed. The frontier molecular orbital approach was applied and a good correlation between the LUMO energies of the Lewis acid–CBS–naphthoquinone adducts and kDA could be found. For the SnCl4–CBS–naphthoquinone adduct an unusual distortion was observed leading to an enhanced Lewis acidity. Energy decomposition analysis with natural orbitals for chemical valence (EDA‐NOCV) calculations revealed the relevant interactions and activation mode of SnCl4 as Lewis acid in Diels–Alder reactions. 相似文献
968.
969.
Dr. Huifang Li Lisheng Zhang lvyin Zheng Dr. Xun Li Dr. Xiaolin Fan Dr. Yi Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14285-14292
Phototriggered intramolecular isomerization in a series of ruthenium sulfoxide complexes, [Ru(L)(tpy)(DMSO)]n+ (where tpy=2,2’:6’,2’’‐terpyridine; DMSO=dimethyl sulfoxide; L=2,2’‐bipyridine (bpy), n=2; N,N,N’,N’‐tetramethylethylenediamine (tmen) n=2; picolinate (pic), n=1; acetylacetonate (acac), n=1; oxalate (ox), n=0; malonate (mal), n=0), was investigated theoretically. It is observed that the metal‐centered ligand field (3MC) state plays an important role in the excited state S→O isomerization of the coordinated DMSO ligand. If the population of 3MCS state is thermally accessible and no 3MCO can be populated from this state, photoisomerization will be turned off because the 3MCS excited state is expected to lead to fast radiationless decay back to the original 1GSS ground state or photodecomposition along the Ru2+?S stretching coordinate. On the contrary, if the population of 3MCS (or 3MCO) state is inaccessible, photoinduced S→O isomerization can proceed adiabatically on the potential energy surface of the metal‐to‐ligand charge transfer excited states (3MLCTS→3MLCTO). It is hoped that these results can provide valuable information for the excited state isomerization in photochromic d6 transition‐metal complexes, which is both experimentally and intellectually challenging as a field of study. 相似文献
970.
Marco Carboni Dr. Andrea Giacomo Marrani Dr. Riccardo Spezia Dr. Sergio Brutti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(48):17188-17203
The reaction thermodynamics of the 1,2‐dimethoxyethane (DME), a model solvent molecule commonly used in electrolytes for Li?O2 rechargeable batteries, has been studied by first‐principles methods to predict its degradation processes in highly oxidizing environments. In particular, the reactivity of DME towards the superoxide anion O2? in oxygen‐poor or oxygen‐rich environments is studied by density functional calculations. Solvation effects are considered by employing a self‐consistent reaction field in a continuum solvation model. The degradation of DME occurs through competitive thermodynamically driven reaction paths that end with the formation of partially oxidized final products such as formaldehyde and methoxyethene in oxygen‐poor environments and methyl oxalate, methyl formate, 1‐formate methyl acetate, methoxy ethanoic methanoic anhydride, and ethylene glycol diformate in oxygen‐rich environments. This chemical reactivity indirectly behaves as an electroactive parasitic process and therefore wastes part of the charge exchanged in Li?O2 cells upon discharge. This study is the first complete rationale to be reported about the degradation chemistry of DME due to direct interaction with O2?/O2 molecules. These findings pave the way for a rational development of new solvent molecules for Li?O2 electrolytes. 相似文献