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Maximilian W. Kuntze-Fechner Hendrik Verplancke Lukas Tendera Martin Diefenbach Ivo Krummenacher Holger Braunschweig Todd B. Marder Max C. Holthausen Udo Radius 《Chemical science》2020,11(40):11009
The reaction of [Ni(Mes2Im)2] (1) (Mes2Im = 1,3-dimesityl-imidazolin-2-ylidene) with polyfluorinated arenes as well as mechanistic investigations concerning the insertion of 1 and [Ni(iPr2Im)2] (1ipr) (iPr2Im = 1,3-diisopropyl-imidazolin-2-ylidene) into the C–F bond of C6F6 is reported. The reaction of 1 with different fluoroaromatics leads to formation of the nickel fluoroaryl fluoride complexes trans-[Ni(Mes2Im)2(F)(ArF)] (ArF = 4-CF3-C6F42, C6F53, 2,3,5,6-C6F4N 4, 2,3,5,6-C6F4H 5, 2,3,5-C6F3H26, 3,5-C6F2H37) in fair to good yields with the exception of the formation of the pentafluorophenyl complex 3 (less than 20%). Radical species and other diamagnetic side products were detected for the reaction of 1 with C6F6, in line with a radical pathway for the C–F bond activation step using 1. The difluoride complex trans-[Ni(Mes2Im)2(F)2] (9), the bis(aryl) complex trans-[Ni(Mes2Im)2(C6F5)2] (15), the structurally characterized nickel(i) complex trans-[NiI(Mes2Im)2(C6F5)] (11) and the metal radical trans-[NiI(Mes2Im)2(F)] (12) were identified. Complex 11, and related [NiI(Mes2Im)2(2,3,5,6-C6F4H)] (13) and [NiI(Mes2Im)2(2,3,5-C6F3H2)] (14), were synthesized independently by reaction of trans-[Ni(Mes2Im)2(F)(ArF)] with PhSiH3. Simple electron transfer from 1 to C6F6 was excluded, as the redox potentials of the reaction partners do not match and [Ni(Mes2Im)2]+, which was prepared independently, was not detected. DFT calculations were performed on the insertion of [Ni(iPr2Im)2] (1ipr) and [Ni(Mes2Im)2] (1) into the C–F bond of C6F6. For 1ipr, concerted and NHC-assisted pathways were identified as having the lowest kinetic barriers, whereas for 1, a radical mechanism with fluoride abstraction and an NHC-assisted pathway are both associated with almost the same kinetic barrier.A combined experimental and theoretical study on the mechanism of the C–F bond activation of C6F6 with [Ni(NHC)2] is provided. 相似文献
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Morelos A Albuquerque IF Bondar NF Carrigan RA Chen D Cooper PS Lisheng D Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Foucher M Golovtsov VL Gottschalk H Gouffon P Grachev VT Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Lang Pengfei Li Chengze Li Yunshan Luksys M Mahon JR McCliment E Newsom C Pommot Maia MC Samsonov VM Schegelsky VA Shi Huanzhang Smith VJ Tang Fukun Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Yan Jie Zhao Wenheng Shuchen Z Zhong Yuanyuan 《Physical review letters》1993,71(21):3417-3420
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Morelos A Albuquerque IF Bondar NF Carrigan RA Chen D Cooper PS Dai Lisheng Denisov AS Dobrovolsky AV Dubbs T Endler AM Escobar CO Foucher M Golovtsov VL Gottschalk H Gouffon P Grachev VT Khanzadeev AV Kubantsev MA Kuropatkin NP Lach J Lang Pengfei Li Chengze Li Yunshan Luksys M Mahon JR McCliment E Newsom C Pommot Maia MC Samsonov VM Schegelsky VA Shi Huanzhang Smith VJ Tang Fukun Terentyev NK Timm S Tkatch II Uvarov LN Vorobyov AA Yan Jie Zhao Wenheng Zheng Shuchen Zhong Yuanyuan 《Physical review letters》1993,71(14):2172-2175
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Yi SS Reichert EL Holthausen MC Koch W Weisshaar JC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(12):2232-2245
A pulsed beam of Co+(3F4) crosses a pulsed beam of C3H8 or C3D8 gas under single collision conditions at collision energies of 0.01 eV and 0.21 eV. After a variable time delay t(ext) = 1-8 micros a fast high voltage pulse extracts product ions into a field-free flight tube for mass analysis. Consistent with earlier work, we observe prompt CoC3H6+ +H2 elimination products in 3:1 excess over CoC2H4+ +CH4 products at 0.21 eV on a 2-10 micros time scale. Long-lived CoC3H8+ complexes fragment predominantly back to Co+ +C3H8 reactants and to H2 elimination products on a 6-24 micros time scale. Density functional theory (B3LYP) calculations provide energies, geometries, and harmonic vibrational frequencies at key stationary points for use in a statistical rate model of the reaction. By adjusting two key multicenter transition state (MCTS) energies downward by 4-7 kcal mol(-1), we obtain good agreement with our decay time results and with the cross section versus collision energy of Armentrout and co-workers from 0.1-1.0 eV. B3LYP theory succeeds in finding relative energies of the MCTSs leading to CH4 and H2 in the proper order to explain the different product branching ratio for Co+ (which favors H2 over CH4) compared with its nearest neighbors Fe+ and Ni+ (which favor CH4 over H2). 相似文献
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Teixeira-Neto É Leite CA Cardoso AH Medeiros da Silva MC Braga M Galembeck F 《Journal of colloid and interface science》2000,231(1):182-189
Poly(styrene-co-acrylamide) (PS-AAM) latex was prepared, fractionated by sedimentation under gravity, and characterized by PCS, infrared spectra, secondary and backscattered electron imaging in the scanning electron microscope, and electron spectroscopy imaging in an analytical transmission electron microscope. Three latex fractions were obtained. The lower fraction was opalescent and its particles were the more uniform, concerning size, chemical composition, and topochemical features. This lower fraction was still further fractionated by zonal centrifugation in a density gradient, yielding two fractions with similar macrocrystal-forming abilities but different sizes and chemical compositions. These results confirm those previously obtained for the PS-HEMA latex. Copyright 2000 Academic Press. 相似文献
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Hölscher M Leitner W Holthausen MC Frenking G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(16):4700-4708
Quantum chemical calculations by using density functional theory at the B3LYP level have been carried out to elucidate the reaction course for the addition of ethylene to [OsO2(CH2)2] (1). The calculations predict that the kinetically most favorable reaction proceeds with an activation barrier of 8.1 kcal mol(-1) via [3+2] addition across the O=Os=CH2 moiety. This reaction is -42.4 kcal mol(-1) exothermic. Alternatively, the [3+2] addition to the H2C=Os=CH2 fragment of 1 leads to the most stable addition product 4 (-72.7 kcal mol(-1)), yet this process has a higher activation barrier (13.0 kcal mol(-1)). The [3+2] addition to the O=Os=O fragment yielding 2 is kinetically (27.5 kcal mol(-1)) and thermodynamically (-7.0 kcal mol(-1)) the least favorable [3+2] reaction. The formal [2+2] addition to the Os=O and Os=CH2 double bonds proceeds by initial rearrangement of 1 to the metallaoxirane 1 a. The rearrangement 1-->1 a and the following [2+2] additions have significantly higher activation barriers (>30 kcal mol(-1)) than the [3+2] reactions. Another isomer of 1 is the dioxoosmacyclopropane 1 b, which is 56.2 kcal mol(-1) lower in energy than 1. The activation barrier for the 1-->1 b isomerization is 15.7 kcal mol(-1). The calculations predict that there are no energetically favorable addition reactions of ethylene with 1 b. The isomeric form 1 c containing a peroxo group is too high in energy to be relevant for the reaction course. The accuracy of the B3LYP results is corroborated by high level post-HF CCSD(T) calculations for a subset of species. 相似文献