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171.
Fe or FeNO Catalysis? A Quantum Chemical Investigation of the [Fe(CO)3(NO)]−‐Catalyzed Cloke–Wilson Rearrangement 下载免费PDF全文
Johannes E. M. N. Klein Dr. Gerald Knizia Dr. Burkhard Miehlich Prof. Dr. Johannes Kästner Prof. Dr. Bernd Plietker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7254-7257
A quantum chemical investigation of the Bu4N[Fe(CO)3(NO)]‐catalyzed Cloke–Wilson rearrangement of vinyl cyclopropanes is reported. It was found that allylic C?C bond activation can proceed through a SN2′ or SN2‐type mechanism. The application of the recently reported intrinsic bond orbital (IBO) method for all structures indicated that one Fe?N π bond is directly involved. Further analysis showed that during the reaction oxidation occurs at the NO ligand exclusively. 相似文献
172.
Bis[N,N′‐diisopropylbenzamidinato(−)]silicon(II): Lewis Acid/Base Reactions with Triorganylboranes 下载免费PDF全文
Konstantin Junold Johannes A. Baus Dr. Christian Burschka Dr. Célia Fonseca Guerra Prof. Dr. F. Matthias Bickelhaupt Prof. Dr. Reinhold Tacke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12411-12415
Reaction of the donor‐stabilized silylene 1 (which is three‐coordinate in the solid state and four‐coordinate in solution) with BEt3 and BPh3 leads to the formation of the Lewis acid/base complexes 2 and 3 , respectively, which are the first five‐coordinate silicon compounds with an Si?B bond. These compounds were structurally characterized by crystal structure analyses and by multinuclear NMR spectroscopic studies in the solid state and in solution. Additionally, the bonding situation in 2 and 3 was analyzed by quantum chemical studies. 相似文献
173.
Sébastien Perdriau Mu‐Chieh Chang Dr. Edwin Otten Prof. Dr. Hero J. Heeres Prof. Dr. Johannes G. de Vries 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(47):15434-15442
The [Ru(CO)H(PNN)] pincer complex based on a dearomatised PNN ligand (PNN: 2‐di‐tert‐butylphosphinomethyl‐6‐diethylaminomethylpyridine) was examined for its ability to isomerise alkenes. The isomerisation reaction proceeded under mild conditions after activation of the complex with alcohols. Variable‐temperature (VT) NMR experiments to investigate the role of the alcohol in the mechanism lend credence to the hypothesis that the first step involves the formation of a rearomatised alkoxide complex. In this complex, the hemilabile diethylamino side‐arm can dissociate, allowing alkene binding cis to the hydride, enabling insertion of the alkene into the metal–hydride bond, whereas in the parent complex only trans binding is possible. During this study, a new uncommon Ru0 coordination complex was also characterised. The scope of the alkene isomerisation reaction was examined. 相似文献
174.
Antiaromaticity to Aromaticity: From Boroles to 1,2‐Azaborinines by Ring Expansion with Azides 下载免费PDF全文
Prof. Dr. Holger Braunschweig Dr. Christian Hörl Lisa Mailänder Dr. Krzysztof Radacki Dr. Johannes Wahler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9858-9861
We have exploited the reactivity of antiaromatic boroles, gaining access to aryl‐substituted monocyclic 1,2‐azaborinines. The observed ring‐expansion reaction of inherently electron‐deficient boroles with organometallic and organic azides is demonstrated for representative examples. This substance class is expected to provide a new avenue into 1,2‐azaborinine chemistry, especially in the area of functional organoboron materials. Our results are based on NMR and UV/Vis spectroscopy as well as single‐crystal X‐ray crystallography and provide a virtually quantitative approach that also offers numerous points of variation. 相似文献
175.
Asymmetric Cascade Reaction to Allylic Sulfonamides from Allylic Alcohols by Palladium(II)/Base‐Catalyzed Rearrangement of Allylic Carbamates 下载免费PDF全文
Dipl.‐Chem. Johannes Moritz Bauer Dr. Wolfgang Frey Prof. Dr. René Peters 《Angewandte Chemie (International ed. in English)》2014,53(29):7634-7638
A regio‐ and enantioselective tandem reaction is reported capable of directly transforming readily accessible achiral allylic alcohols into chiral sulfonyl‐protected allylic amines. The reaction is catalyzed by the cooperative action of a chiral ferrocene palladacycle and a tertiary amine base and combines high step‐economy with operational simplicity (e.g. no need for inert‐gas atmosphere or catalyst activation). Mechanistic studies support a PdII‐catalyzed [3,3] rearrangement of allylic carbamates—generated in situ from the allylic alcohol and an isocyanate—as the key step, which is followed by a decarboxylation. 相似文献
176.
A Molecular Approach to Self‐Supported Cobalt‐Substituted ZnO Materials as Remarkably Stable Electrocatalysts for Water Oxidation 下载免费PDF全文
Johannes Pfrommer Dr. Michael Lublow Anahita Azarpira Dr. Caren Göbel Marcel Lücke Dr. Alexander Steigert Martin Pogrzeba Dr. Prashanth W. Menezes Dr. Anna Fischer Dr. Thomas Schedel‐Niedrig Prof. Dr. Matthias Driess 《Angewandte Chemie (International ed. in English)》2014,53(20):5183-5187
In regard to earth‐abundant cobalt water oxidation catalysts, very recent findings show the reorganization of the materials to amorphous active phases under catalytic conditions. To further understand this concept, a unique cobalt‐substituted crystalline zinc oxide (Co:ZnO) precatalyst has been synthesized by low‐temperature solvolysis of molecular heterobimetallic Co4?xZnxO4 (x=1–3) precursors in benzylamine. Its electrophoretic deposition onto fluorinated tin oxide electrodes leads after oxidative conditioning to an amorphous self‐supported water‐oxidation electrocatalyst, which was observed by HR‐TEM on FIB lamellas of the EPD layers. The Co‐rich hydroxide‐oxidic electrocatalyst performs at very low overpotentials (512 mV at pH 7; 330 mV at pH 12), while chronoamperometry shows a stable catalytic current over several hours. 相似文献
177.
Dipl.‐Chem. Johannes Broichhagen Innokentij Jurastow Katharina Iwan Prof. Dr. Wolfgang Kummer Prof. Dr. Dirk Trauner 《Angewandte Chemie (International ed. in English)》2014,53(29):7657-7660
Photochromic ligands have been used to control a variety of biological functions, especially in neural systems. Recently, much effort has been invested in the photocontrol of ion channels and G‐protein coupled receptors found in the synapse. Herein, we describe the expansion of our photopharmacological approach toward the remote control of an enzyme. Building on hallmark studies dating from the late 1960s, we evaluated photochromic inhibitors of one of the most important enzymes in synaptic transmission, acetylcholinesterase (AChE). Using structure‐based design, we synthesized several azobenzene analogues of the well‐known AChE inhibitor tacrine (THA) and determined their effects on enzymatic activity. One of our compounds, AzoTHA, is a reversible photochromic blocker of AChE in vitro and ex vivo with high affinity and fast kinetics. As such, AzoTHA can be used to control synaptic transmission on the neuromuscular endplate based on the light‐dependent clearance of a neurotransmitter. 相似文献
178.
Artificial Accelerators of the Molecular Chaperone Hsp90 Facilitate Rate‐Limiting Conformational Transitions 下载免费PDF全文
Bettina K. Zierer Matthias Weiwad Martin Rübbelke Lee Freiburger Gunter Fischer Oliver R. Lorenz Michael Sattler Klaus Richter Johannes Buchner 《Angewandte Chemie (International ed. in English)》2014,53(45):12257-12262
The molecular chaperone Hsp90 undergoes an ATP‐driven cycle of conformational changes in which large structural rearrangements precede ATP hydrolysis. Well‐established small‐molecule inhibitors of Hsp90 compete with ATP‐binding. We wondered whether compounds exist that can accelerate the conformational cycle. In a FRET‐based screen reporting on conformational rearrangements in Hsp90 we identified compounds. We elucidated their mode of action and showed that they can overcome the intrinsic inhibition in Hsp90 which prevents these rearrangements. The mode of action is similar to that of the co‐chaperone Aha1 which accelerates the Hsp90 ATPase. However, while the two identified compounds influence conformational changes, they target different aspects of the structural transitions. Also, the binding site determined by NMR spectroscopy is distinct. This study demonstrates that small molecules are capable of triggering specific rate‐limiting transitions in Hsp90 by mechanisms similar to those in protein cofactors. 相似文献
179.
Tetracyanoquinodimethane Reduction by Complexed Guanidinyl‐Functionalized Aromatic Compounds 下载免费PDF全文
Hendrik Herrmann Alexandra Ziesak Ute Wild Simone Leingang David Schrempp Norbert Wagner Prof. Dr. Johannes Beck Dr. Elisabeth Kaifer Prof. Dr. Hubert Wadepohl Prof. Dr. Hans‐Jörg Himmel 《Chemphyschem》2014,15(2):351-365
In this work, we report on the reduction of tetracyanoquinodimethane (TCNQ) with dicationic complexes of guanidinyl‐functionalized aromatic (GFA) electron donors. In contrast to reduction with free GFAs, milder reduction conditions were achieved, and this led to semiconducting materials with extended TCNQ π stacking. The charge on the TCNQ units was estimated from the structural data obtained by single‐crystal X‐ray diffraction analysis and from IR spectroscopic data. The electrical conductivity was studied and the activation energy of the semiconducting materials was estimated from the temperature dependence of the conductivity. 相似文献
180.