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61.
Katharina Dilchert Michelle Schmidt Angela Großjohann Kai‐Stephan Feichtner Robert E. Mulvey Viktoria H. Gessner 《Angewandte Chemie (International ed. in English)》2021,60(1):493-498
s‐Block metal carbenoids are carbene synthons and applied in a myriad of organic transformations. They exhibit a strong structure–activity relationship, but this is only poorly understood due to the challenging high reactivity and sensitivity of these reagents. Here, we report on systematic VT and DOSY NMR studies, XRD analyses as well as DFT calculations on a sulfoximinoyl‐substituted model system to explain the pronounced solvent dependency of the carbenoid stability. While the sodium and potassium chloride carbenoids showed high stabilities independent of the solvent, the lithium carbenoid was stable at room temperature in THF but decomposed at ?10 °C in toluene. These divergent stabilities could be explained by the different structures formed in solution. In contrast to simple organolithium reagents, the monomeric THF‐solvate was found to be more stable than the dimer in toluene, since the latter more readily forms direct Li/Cl interactions which facilitate decomposition via α‐elimination. 相似文献
62.
Gessner VH Koller SG Strohmann C Hogan AM O'Shea DF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(10):2996-3004
This article addresses the mechanistic features of asymmetric carbolithiation of β‐methylstyrenes. While often the presence of functional groups is required to obtain high enantioselectivities in carbolithiation reactions, simple β‐methylstyrene also gives high selectivities in (?)‐sparteine‐mediated addition of alkyl lithium compounds. Computational studies on the carbolithiation of β‐methylstyrene with (?)‐sparteine show that the observed selectivities are the result of repulsion effects in the diastereomeric transition states between the (?)‐sparteine ? alkyl lithium adduct and the β‐methylstyrene, upon approximation of the two reactants. In contrast, for the ortho‐amino β‐methylstyrene (E)‐benzyl(2‐propenylphenyl)amine ( 4 ) X‐ray structure analyses of intermediate lithium amides indicate a carbolithiation mechanism in which one side of the double bond is shielded by the amide moiety, leaving only one side free for approach of the chiral alkyl lithium adduct. 相似文献
63.
Viktoria Falkowski Alexander Zeugner Anna Isaeva Klaus Wurst Michael Ruck Hubert Huppertz 《无机化学与普通化学杂志》2019,645(14):911-911
64.
Christopher Schwarz Lennart T. Scharf Thorsten Scherpf Dr. Julia Weismann Prof. Dr. Viktoria H. Gessner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(11):2793-2802
The isolation and structural characterization of the cyanido-substituted metalated ylides [Ph3P−C−CN]M ( 1-M ; M=Li, Na, K) are reported with lithium, sodium, and potassium as metal cations. In the solid-state, most different aggregates could be determined depending on the metal and additional Lewis bases. The crown-ether complexes of sodium ( 1-Na ) and potassium ( 1-K ) exhibited different structures, with sodium preferring coordination to the nitrogen end, whereas potassium binds in an unusual η2-coordination mode to the two central carbon atoms. The formation of the yldiide was accompanied by structural changes leading to shorter C−C and longer C−N bonds. This could be attributed to the delocalization of the free electron pairs at the carbon atom into the antibonding orbitals of the CN moiety, which was confirmed by IR spectroscopy and computational studies. Detailed density functional theory calculations show that the changes in the structure and the bonding situation were most pronounced in the lithium compounds due to the higher covalency. 相似文献
65.
66.
Christian Däschlein Dr. Viktoria H. Gessner Dr. Carsten Strohmann Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(13):4048-4062
The direct α‐lithiation of methyl‐substituted silanes as an efficient method for the preparation and elaboration of Si‐chiral compounds is reported. Deprotonation of chiral oligosilanes occurs selectively and with high yields at the methyl group of the stereogenic silicon center, even in the presence of multiple methylsilyl or methylgermyl substituents. Computational studies have confirmed this preference as a consequence of pre‐coordination of the lithiating agent by the amino side‐arm and repulsion effects in the corresponding transition state. This complexation is also obvious from X‐ray structure analyses of the α‐lithiated silanes, which exhibit intriguing structure formation patterns differing in the type of aggregation and the amount of alkyllithium used. An alternative route to Si‐chiral compounds is also presented, which involves desymmetrization of dimethylsilanes mediated by a chiral side‐arm. Structure analyses and computational studies have shown that the diastereoselectivity of this α‐lithiation is influenced by the selectivity of the formation of the stereogenic nitrogen upon complexation of the alkyllithium. 相似文献
67.
Rychkov Vladimir N. Semenishchev Vladimir S. Kirillov Evgeny V. Kirillov Sergey V. Ryabukhina Viktoria G. Smyshlyaev Denis V. Bunkov Grigory M. Botalov Maxim S. 《Journal of Radioanalytical and Nuclear Chemistry》2018,317(1):203-213
Journal of Radioanalytical and Nuclear Chemistry - The paper deals with two rare earth elements (REE) concentrates recovered from uranium leach liquors after sorption separation of uranium.... 相似文献
68.
69.
Rodrigo Beltrn-Suito Viktoria Forstner J. Niklas Hausmann Stefan Mebs Johannes Schmidt Ivelina Zaharieva Konstantin Laun Ingo Zebger Holger Dau Prashanth W. Menezes Matthias Driess 《Chemical science》2020,11(43):11834
An unprecedented molecular 2Fe–2As precursor complex was synthesized and transformed under soft reaction conditions to produce an active and long-term stable nanocrystalline FeAs material for electrocatalytic water oxidation in alkaline media. The 2Fe2As-centred β-diketiminato complex, having an unusual planar Fe2As2 core structure, results from the salt-metathesis reaction of the corresponding β-diketiminato FeIICl complex and the AsCO− (arsaethynolate) anion as the monoanionic As− source. The as-prepared FeAs phase produced from the precursor has been electrophoretically deposited on conductive electrode substrates and shown to act as a electro(pre)catalyst for the oxygen evolution reaction (OER). The deposited FeAs undergoes corrosion under the severe anodic alkaline conditions which causes extensive dissolution of As into the electrolyte forming finally an active two-line ferrihydrite phase (Fe2O3(H2O)x). Importantly, the dissolved As in the electrolyte can be fully recaptured (electro-deposited) at the counter electrode making the complete process eco-conscious. The results represent a new and facile entry to unexplored nanostructured transition-metal arsenides and their utilization for high-performance OER electrocatalysis, which are also known to be magnificent high-temperature superconductors.A molecularly derived FeAs has been used as an electro(pre)catalyst for an efficient alkaline OER for the first time and subsequently, its active structure has been determined by quasi in situ X-ray absorption spectroscopy and ex situ methods. 相似文献
70.
Sergiy O. Nikitin Rostyslav D. Lampeka Yulian M. Volovenko Tetyana A. Volovnenko Viktoria V. Dyakonenko Svitlana V. Shishkina Oleg V. Shishkin 《Polyhedron》2008
A series of new 3d-metal complexes based on 2-amino-3-(1-methylbenzimidazol-2-yl)-4(5H)-ketothiophen (HL1) and 2-amino-3-(2-benzothiazolyl)-4(5H)-ketothiophen (HL2) were synthesized. Compounds of the general formulas [ML2] and [M(HL1)2Cl2] (where M = Co2+, Ni2+, Zn2+, Cu2+) were prepared by the reaction of the above mentioned ligands with the corresponding acetate (for [ML2]) or chloride (for [M(HL1)2Cl2]) salts in a methanol or a methanol–chloroform medium. The choice of the anion in the initial metal salt, as well as the selection of the ligand, is crucial for obtaining coordination compounds with a neutral or deprotonated form of the 2-amino-4(5H)-ketothiophens. Thus, in contrast to HL1, complexes with the neutral form of HL2 cannot be obtained under the same conditions. All the complexes were studied by spectroscopic methods and X-ray crystallography (for [CuL12] · H2O). The coordination polyhedron of the copper atom is formed by four nitrogen atoms from two ligand anions and the geometry of the coordination sphere is intermediate between tetrahedral and square-planar. 相似文献