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排序方式: 共有104条查询结果,搜索用时 15 毫秒
91.
92.
Oldenburg PD Feng Y Pryjomska-Ray I Ness D Que L 《Journal of the American Chemical Society》2010,132(50):17713-17723
Iron(II) complexes of a series of N-acylated dipyridin-2-ylmethylamine ligands (R-DPAH) have been investigated as catalysts for the cis-dihydroxylation of olefins to model the action of Rieske dioxygenases that catalyze arene cis-dihydroxylation. The Rieske dioxygenases have a mononuclear iron active site coordinated to a 2-histidine-1-carboxylate facial triad motif. The R-DPAH ligands are designed to provide a facial N,N,O-ligand set that mimics the enzyme active site. The iron(II) complexes of the R-DPAH ligands activate H(2)O(2) to effect the oxidation of olefin substrates into cis-diol products. As much as 90% of the H(2)O(2) oxidant is converted into cis-diol, but a large excess of olefin is required to achieve the high conversion efficiency. Reactivity and mechanistic comparisons with the previously characterized Fe(TPA)/H(2)O(2) catalyst/oxidant combination (TPA = tris(pyridin-2-ylmethyl)amine) lead us to postulate an Fe(II)/Fe(IV) redox cycle for the Fe(R-DPAH) catalysts in which an Fe(IV)(OH)(2) oxidant carries out the cis-hydroxylation of olefins. This hypothesis is supported by three sets of observations: (a) the absence of a lag phase in the conversion of the H(2)O(2) oxidant into a cis-diol product, thereby excluding the prior oxidation of the Fe(II) catalyst to an Fe(III) derivative as established for the Fe(TPA) catalyst; (b) the incorporation of H(2)(18)O into the cis-diol product, thereby requiring O-O bond cleavage to occur prior to cis-diol formation; and (c) the formation of cis-diol as the major product of cyclohexene oxidation, rather than the epoxide or allylic alcohol products more commonly observed in metal-catalyzed oxidations of cyclohexene, implicating an oxidant less prone to oxo transfer or H-atom abstraction. 相似文献
93.
Katrin Meier Raul Cardoso‐Gil Walter Schnelle Helge Rosner Ulrich Burkhardt Ulrich Schwarz PD Dr. 《无机化学与普通化学杂志》2010,636(8):1466-1473
A series of isotypic rare‐earth metal pentagermanides including the new compound TbGe5 were prepared by high‐pressure synthesis. They crystallize in the orthorhombic space group Immm [No. 71; a = 395.70(9) pm; b = 611.1(2) pm, and c = 983.6(3) pm for TbGe5]. The crystal structure is isotypic to LaGe5 and consists of puckered germanium slabs, which sandwich a second germanium species and the rare‐earth metal atoms. At ambient pressure, the thermal decomposition of the phases REGe5 (RE = La, Nd, Sm, Gd, and Tb) proceeds via discrete intermediate steps into Ge(cF8) and thermodynamically stable germanium‐poorer phases. The investigated compounds REGe5 are paramagnetic metallic conductors, which order antiferromagnetically at low temperatures. Specific heat measurements reveal that the superconducting state of LaGe5 below Tc = 7.1(1) K is characterized by a critical field of μ0Hc2 = 0.2 T and weak electron‐phonon coupling. Density‐functional based band‐structure calculations yield a very similar electronic structure for all the isotypic REGe5 compounds. Besides a slight increase in the width of the valence band for smaller RE atoms, only minor differences are found for the two different germanium environments. 相似文献
94.
Diaryl‐substituted triazenides Ar(Ar′)N3HgX [Ar/Ar′ = Dmp/Mph, X = Cl ( 2a ), Br ( 3a ), I ( 4a ); Ar/Ar′ = Dmp/Tph, X = Cl ( 2b ), I ( 4b ) with Mph = 2‐MesC6H4, Mes = 2,4,6‐Me3C6H2, Tph = 2′,4′,6′‐triisopropylbiphenyl‐2‐yl and Dmp = 2,6‐Mes2C6H3] were synthesized by salt‐metathesis reactions in ethyl ether from the readily available starting materials Ar(Ar′)N3Li and HgX2. These compounds may be used for redox‐transmetallation reactions with rare‐earth or alkaline earth metals. Thus, reaction of 4b or 2b with magnesium or ytterbium in tetrahydrofuran afforded the triazenides Dmp(Tph)N3MX(thf) ( 5b : M = Mg, X = I; 6b : M = Yb, X = Cl) in good yield. All new compounds were characterized by melting point, 1H and 13C NMR spectroscopy and for selected species by IR spectroscopy or mass spectrometry. In addition, the solid‐state structures of triazenides 2a , 2b , 3a , 4b , 5b and 6b were investigated by single‐crystal X‐ray diffraction. 相似文献
95.
Christian Schenk Florian Henke Marco Neumaier Matthias Olzmann Hansgeorg Schnöckel Prof. Dr. Andreas Schnepf PD Dr. 《无机化学与普通化学杂志》2010,636(7):1173-1182
The cluster anion {Ge9[Si(SiMe3)3]3}– ( 1 ) is transferred intact into the gas phase via the electro spray method. Subsequently the fragmentation of 1 after resonant excitation as well as the oxidation reaction with O2 and Cl2 are investigated in an FT‐ICR mass spectrometer (Fourier Transform Ion Cyclotron Resonance). Unlike former results with off‐resonant excitation the fragmentation leads mainly to the end‐product Ge9–. Moreover, applying an on‐resonant excitation the dissociation experiment can be quantified; 2.0 ± 0.15 eV (193 ± 15kJ · mol–1) for the elimination of the first two ligands and 2.7 ± 0.15 eV (261 ± 15 kJ · mol–1) for all ligands, respectively. Particular attention is turned on the first step, where sterically encumbered Si2(SiMe3)6 molecules are formed in a concerted reaction. This result, which is also important for elemental reactions on metal surfaces in catalyses, is based on experimentally determined threshold energies, DFT calculations and calculations on the lifetime of the involved species., In contrast to the high reactivity of crystalline 1 ·Li(THF)4, gaseous 1 is inert against oxygen. The analogy to recently published spin forbidden reactions of Al13– with O2 hints to a general importance of spin conversion during gas phase reactions of larger cluster molecules. The oxidation of 1 with Cl2 proceeds through different reaction channels. DFT calculations give a first insight on the complex primary oxidation steps. These calculations also reveal that the delocalized bonding situation in the Ge9 core is distorted upon oxidation. This result together with the dissociation experiments shed more light on differences and similarities between metalloid clusters and Zintl ions. 相似文献
96.
97.
Novel alkali trimolybdates of the triclinic (M, M′)2Mo3O10 (M = Rb; M′ = K, Cs) type were obtained through a systematic hydrothermal approach based on the reaction of MoO3 with alkali halide solutions at 180 °C. The crystal structures were determined from X‐ray single crystal data. The alkali trimolybdates extend the family of known alkali trimolybdates in an unexpected fashion, because they contain a distorted variation of [Mo3O10]2? chains as a key structural motif that has only been found in a single compound before, namely ethylenediammonium trimolybdate, (C2H10N2)[Mo3O10]. The applied hydrothermal strategy is discussed in the general context of systematic pathways to polyoxomolybdates. Furthermore, the templating role of the alkali cations and their interaction with the polyoxomolybdate surroundings is compared to (C2H10N2)[Mo3O10] in terms of electrostatic calculations. 相似文献
98.
99.
100.
Curtis M. Oldenburg Jennifer L. Lewicki Laura Dobeck Lee Spangler 《Transport in Porous Media》2010,82(1):77-92
We used the multiphase and multicomponent TOUGH2/EOS7CA model to carry out predictive simulations of CO2 injection into the shallow subsurface of an agricultural field in Bozeman, Montana. The purpose of the simulations was to
inform the choice of CO2 injection rate and design of monitoring and detection activities for a CO2 release experiment. The release experiment configuration consists of a long horizontal well (70 m) installed at a depth of
approximately 2.5 m into which CO2 is injected to mimic leakage from a geologic carbon sequestration site through a linear feature such as a fault. We estimated
the permeability of the soil and cobble layers present at the site by manual inversion of measurements of soil CO2 flux from a vertical-well CO2 release. Based on these estimated permeability values, predictive simulations for the horizontal well showed that CO2 injection just below the water table creates an effective gas-flow pathway through the saturated zone up to the unsaturated
zone. Once in the unsaturated zone, CO2 spreads out laterally within the cobble layer, where liquid saturation is relatively low. CO2 also migrates upward into the soil layer through the capillary barrier and seeps out at the ground surface. The simulations
predicted a breakthrough time of approximately two days for the 100kg d−1 injection rate, which also produced a flux within the range desired for testing detection and monitoring approaches. The
seepage area produced by the model was approximately five meters wide above the horizontal well, compatible with the detection
and monitoring methods tested. For a given flow rate, gas-phase diffusion of CO2 tends to dominate over advection near the ground surface, where the CO2 concentration gradient is large, while advection dominates deeper in the system. 相似文献