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31.
Podkolzin SG Manoilova OV Weckhuysen BM 《The journal of physical chemistry. B》2005,109(23):11634-11642
Relative activity of La2O3, LaOCl, and LaCl3 in the destructive adsorption of CCl4 to CO2 was studied with density-functional theory calculations and temperature-programmed reaction experiments monitored with IR spectroscopy. Integral absorbance of the IR peak for phosgene, which is a reaction intermediate, was obtained as a function of temperature, and initial reaction temperatures were compared for different sample amounts of La2O3 and LaOCl. The initial reaction temperatures of about 390 K for La2O3 and 365 K for LaOCl were practically independent of the tested sample weights, and the lower temperature for LaOCl was attributed to a higher activity of surface sites on this material. Calculations suggest that CCl4 decomposition proceeds through a stepwise Cl donation from CCl4 to the surface and that the overall rate is controlled by the first step: CCl4 splitting into a Cl anion and CCl3 cation over an acid-base pair of surface sites. A lanthanum acid site in the pair initiates the split by interacting with one of the chlorine atoms in CCl4, and an oxygen base site stabilizes the remaining CCl3 fragment. Transition state estimates suggest that the relative activity of surface sites can be ranked in the following order: LaOCl > LaCl3 with a partially dechlorinated surface > La2O3. Surface Lewis acidity and basicity of these materials are summarized in terms of the vibrational frequency for adsorbed CO, energy of the lowest unoccupied molecular orbital, and proton affinity. Higher activity of LaOCl is attributed to the higher acidity of the lanthanum site, the higher basicity of the oxygen site, and the geometry of the acid-base pair of sites that allows them to interact with CCl4 simultaneously. 相似文献
32.
McClenaghan ND Passalacqua R Loiseau F Campagna S Verheyde B Hameurlaine A Dehaen W 《Journal of the American Chemical Society》2003,125(18):5356-5365
Three new luminescent and redox-active Ru(II) complexes containing novel dendritic polypyridine ligands have been synthesized, and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox behavior have been investigated. The dendritic ligands are made of 1,10-phenanthroline coordinating subunits and of carbazole groups as branching sites. The first and second generation species of this novel class of dendritic ligands (L1 and L2, respectively; see Figure 1 for their structural formulas) have been prepared and employed. The metal dendrimers investigated are [Ru(bpy)(2)(L1)](2+) (1; bpy = 2,2'-bipyridine), [Ru(bpy)(2)(L2)](2+) (2), and [Ru(L1)(3)](2+) (3; see Figure 2). For the sake of completeness and comparison purposes, also the absorption spectra, redox behavior, and luminescence properties of L1 and L2 have been studied, together with the properties of 3,6-di(tert-butyl)carbazole (L0) and [Ru(bpy)(2)(phen)](2+) (4, phen = 1,10-phenanthroline). The absorption spectra of the free dendritic ligands show features which can be assigned to the various subunits (i.e., carbazole and phenanthroline groups) and additional bands at lower energies (at lambda > 300 nm) which are assigned to carbazole-to-phenanthroline charge-transfer (CT) transitions. These latter bands are significantly red-shifted upon acid and/or zinc acetate addition. Both L1 and L2 exhibit relatively intense luminescence at room temperature in fluid solution (lifetimes in the nanosecond time scale, quantum yields of the order of 10(-2)-10(-1)) and at 77 K in rigid matrix (lifetimes in the millisecond time scale). Such a luminescence is assigned to CT states at room temperature and to phenanthroline-centered pi-pi triplet levels at 77 K. The room-temperature luminescence of L1 and L2 is totally quenched by acid or zinc acetate. The metal dendrimers exhibit the typical absorption and luminescence properties of Ru(II) polypyridine complexes. In particular, metal-to-ligand charge-transfer (MLCT) bands dominate the visible absorption spectra, and formally triplet MLCT levels govern the excited-state properties. Excitation spectroscopy evidences that all the light absorbed by the dendritic branches is transferred with unitary efficiency to the luminescent MLCT states in 1-3, showing that the new metal dendrimers can be regarded as efficient light-harvesting antenna systems. All the free ligands and metal dendrimers exhibit a rich redox behavior (except L2 and 3, whose redox behavior was not investigated because of solubility reasons), with clearly attributable reversible carbazole- and metal-centered oxidation and polypyridine-centered reduction processes. The electronic interaction between the carbazole redox-active sites of the dendritic ligands is affected by Ru(II) coordination. 相似文献
33.
Bert C. Lynn Mara Tsesarskaja Otto F. Schall Jeanette C. Hernandez Shigeru Watanabe Toshio Takahashi 《Supramolecular chemistry》2013,25(3-4):253-260
Abstract The interactions of macrocyclic polyethers with alkali and alkaline earth cations have been well studied and much about their chemistry is now well understood. Less well examined or comprehended are hydrogen bond interactions. A combination of ion selective electrode binding constant determination techniques and fast atom bombardment mass spectrometry are brought to bear on this problem. It is found that all-oxygen crown ethers and their derivatives exhibit quite different complexation behaviour with ammonium salts than do their various azacrown counterparts. 相似文献
34.
35.
Dr. Kai-Stephan Feichtner Dr. Lennart T. Scharf Dr. Thorsten Scherpf Dr. Bert Mallick Nils Boysen Prof. Dr. Viktoria H. Gessner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(69):17351-17360
The use of iminophosphoryl-tethered ruthenium carbene complexes to activate secondary phosphine P−H bonds is reported. Complexes of type [(p-cymene)-RuC(SO2Ph)(PPh2NR)] (with R = SiMe3 or 4-C6H4−NO2) were found to exhibit different reactivities depending on the electronics of the applied phosphine and the substituent at the iminophosphoryl moiety. Hence, the electron-rich silyl-substituted complex undergoes cyclometallation or shift of the imine moiety after cooperative activation of the P−H bond across the M=C linkage, depending on the electronics of the applied phosphine. Deuteration experiments and computational studies proved that cyclometallation is initiated by the activation process at the M=C bond and triggered by the high electron density at the metal in the phosphido intermediates. Consistently, replacement of the trimethylsilyl (TMS) group by the electron-withdrawing 4-nitrophenyl substituent allowed the selective cooperative P−H activation to form stable activation products. 相似文献
36.
37.
Bert C. Lynn Jesus V. Mallén Servando Muñoz Minsook Kim George W. Gokel 《Supramolecular chemistry》2013,25(3-4):195-197
Abstract Bola-amphiphiles having two aza-18-crown-6 ether rings attached by a covalent spacer (O—O) and an analogous tris (macrocycle) (O—O—O) have been prepared and their cation complexation behavior has been assessed by fast atom bombardment and collisionally activated dissociation tandem mass spectrometry; the key finding is that two cations may simultaneously be complexed by a two- or three-crown system and that this complexation may also involve an anion. 相似文献
38.
Jun‐Yi Chen Zi‐Long Xiang Feng Yu Bert F. Sels Yu Fu Ting Sun Mario Smet Wim Dehaen 《Journal of polymer science. Part A, Polymer chemistry》2014,52(18):2596-2603
A series of hyperbranched polyacenaphthenequinones has been prepared by superelectrophilic aromatic substitution of (substituted) acenaphthenequinone and 1,3,5‐tris‐(4‐phenoxybenzoyl)benzene via a facile A2 + B3 approach. Because of the strongly increased reactivity of the second A functionality, gelation was efficiently avoided during the polymerization. The structure of the resulting polymer was characterized by NMR spectroscopy and gel permeation chromatography. Further modification of the hyperbranched polyacenaphthenequinone was explored both on the acenaphthenequinone and aromatic moieties. Moreover, the polymer modified through sulfonation was investigated as a water‐soluble acid catalyst for the degradation of biomass resources. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2596‐2603 相似文献
39.
Oxidative Addition of Haloheteroarenes to Palladium(0): Concerted versus SNAr‐Type Mechanism
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Prof. Bert U. W. Maes Dr. Stefan Verbeeck Dr. Tom Verhelst Audrey Ekomié Niklas von Wolff Dr. Guillaume Lefèvre Dr. Emily A. Mitchell Prof. Anny Jutand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7858-7865
The kinetics of the oxidative additions of haloheteroarenes HetX (X=I, Br, Cl) to [Pd0(PPh3)2] (generated from [Pd0(PPh3)4]) have been investigated in THF and DMF and the rate constants have been determined. In contrast to the generally accepted concerted mechanism, Hammett plots obtained for substituted 2‐halopyridines and solvent effects reveal a reaction mechanism dependent on the halide X of HetX: an unprecedented SNAr‐type mechanism for X=Br or Cl and a classical concerted mechanism for X=I. These results are supported by DFT studies. 相似文献
40.
A mass‐conservative staggered immersed boundary model for solving the shallow water equations on complex geometries
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Alberto Canestrelli Aukje Spruyt Bert Jagers Rudy Slingerland Mart Borsboom 《国际流体数值方法杂志》2016,81(3):151-177
In this work, an approach is proposed for solving the 3D shallow water equations with embedded boundaries that are not aligned with the underlying horizontal Cartesian grid. A hybrid cut‐cell/ghost‐cell method is used together with a direction‐splitting implicit solver: Ghost cells are used for the momentum equations in order to prescribe the correct boundary condition at the immersed boundary, while cut cells are used in the continuity equation in order to conserve mass. The resulting scheme is robust, does not suffer any time step limitation for small cut cells, and conserves fluid mass up to machine precision. Moreover, the solver displays a second‐order spatial accuracy, both globally and locally. Comparisons with analytical solutions and reference numerical solutions on curvilinear grids confirm the quality of the method. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献