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81.
Joji Ohshita Ryosuke Taketsugu Yuki Nakahara Atsutaka Kunai 《Journal of organometallic chemistry》2004,689(20):3258-3264
Selective dehydrogenative coupling of di- and trihydrosilanes with alcohols catalyzed by PdCl2 or NiCl2 afforded alkoxyhydro- and dialkoxyhydrosilanes in good yield. Further treatment of the resulting alkoxyhydrosilanes with carbon tetrachloride or allyl bromide in the presence of the same catalyst led to the formation of alkoxychloro- and alkoxybromosilanes, respectively. Similar reactions of dialkoxyhydrosilanes with carbon tetrachloride afforded dialkoxychlorosilanes in good yield, although contamination of small amounts of trialkoxysilanes and alkoxydichlorosilanes was detected in the products. Selective substitution of the alkoxyhalosilanes with nucleophiles is also reported. 相似文献
82.
A simple procedure for the synthesis of an important standard, isotopically enriched methylmercury, which is not commercially available, has been established successfully. The isotopically enriched standard synthesized is utilized in conventional isotope dilution mass spectrometry (IDMS), as well as in speciated IDMS (SIDMS), for determination of the true concentration of methylmercury in environmental samples. The CH3201Hg+ standard has been synthesized from commercially available 201HgO and tetramethyltin. The synthesis time required is 1 h at 60°C. The product is highly pure, yielding more than 90% as 201Hg in CH3201Hg+. Hazardous dimethylmercury does not occur during this synthesis procedure. The product synthesized was analyzed using high‐performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (ICP‐MS) and ICP‐MS alone in order to determine its concentration, isotopic composition and purity. The stability of the product was also evaluated for over 6 months and found to be stable at 4°C in the dark. The isotopically enriched methylmercury synthesized can be used in SIDMS and IDMS analyses as a standard. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
83.
A method of nonaqueous capillary zone electrophoresis (CZE) has been developed to characterize block (co)polymers of poly(ethylene oxide) and poly(styrene) containing metallo bis(terpyridine) complexes as bridging units. Specific CZE separation conditions had to be applied, with barium perchlorate dissolved in N-methylformamide (NMF) as background electrolyte and OV-1701-OH deactivated capillaries. For detection UV absorption was measured at a wavelength of 316 nm. Metallo diblock polymers with molecular weights up to 30,000 Da could be analyzed by the proposed nonaqueous CZE method. Experiments performed with polymeric compounds containing Fe, Ni or Ru as central metal ions showed that their electrophoretic mobilities were independent of the type of metal ion. Therefore, the data on the size of the polymeric compounds could be obtained using just one set of calibration standards. Polydispersities of the samples calculated from the experimental results were in correlation with the polydispersities of the polymers used in the synthesis of the metallo diblock polymers. Several polymeric samples contained metallo mono(terpyridine) complexes as impurities. These by-products could be separated from the main product. With symmetrical diblock polymers only one by-product was detected, while with an asymmetric diblock polymer two types of mono-complexes were found. The amount of the mono-complexes present as impurities was dependent on the type of central metal ion (Ni > Fe >> Ru). 相似文献
84.
Vattoly J. MajoJaya Prabhakaran J.John MannJ.S. Dileep Kumar 《Tetrahedron letters》2003,44(47):8535-8537
A novel and convergent palladium catalyzed synthesis of 2-arylbenzothiazoles has been investigated. The key step in the synthesis is a Suzuki biaryl coupling of 2-bromobenzothiazole with aryl boronic acids to provide a variety of 2-arylbenzothiazole derivatives in good yield. The synthetic utility of this methodology is demonstrated by the synthesis of 2-(4-aminophenyl)-6-methoxybenzothiazole, a PET probe precursor for the in vivo imaging of Alzheimer's disease. 相似文献
85.
Leo Brewin 《General Relativity and Gravitation》2007,39(4):521-528
We show by an almost elementary calculation that the ADM mass of an asymptotically flat space can be computed as a limit involving
a rate of change of area of a closed 2-surface. The result is essentially the same as that given by David Brown and York (Phys.
Rev. D 55, 1977–1984 1997; Phys. Rev. D 47, 1407–1419 1993). We will prove this result in two ways, first by direct calculation from the original formula as given by
Arnowitt, Deser and Misner and second as a corollary of an earlier result by Brewin for the case of simplicial spaces. 相似文献
86.
C. D. Habben 《无机化学与普通化学杂志》1991,606(1):229-232
Synthesis of Boron-Sulfur(IV)-Nitrogen Heterocycles The reaction of bis(lithio.tert.-butylamino)phenylborane with tert.-butyldichlorosulfimide and bischlorodimethylsilylsulfodiimide respectively leads to four- or eight-membered heterocycles. The disulfanebridge of one dithiazadiborolidine can be replaced by the ? N?S?N-sequence to yield a Thiatriazadiborine. 1H, 11B, 13C-NMR, mass spectra, and analytical data are reported and discussed. 相似文献
87.
88.
Shayesteh S. Farjami B. Soltani M. A. Solimany 《International Journal of Infrared and Millimeter Waves》2002,23(12):1691-1697
We present and discuss infrared magnetoplasma reflectivity and surface polariton modes in Ga1–xNxAs. It assumed that the sample is characterized by a magnetoplasma dielectric tensor. Surface polariton dispersion for two component magnetoplasma was calculated from reflectivity spectra data. We detect transverse optic phonon of GaN sublattice in 470 cm-1. The origin of sharp feature in p-polarization reflectivity about 300 cm–1 as well as LO phonon frequency of GaAs sublattice is due to Brewster mode. An interesting feature of surface modes in Voigt geometry is nonreciprocalicity, which means that the frequency changes when the direction of propagation is reversed. Also, the infrared magnetoplasma reflectivity of GaNAs should be providing determination of the electrons and heavy holes effective mass and carrier's concentration. 相似文献
89.
Francisco‐Javier Sayas 《Numerical Methods for Partial Differential Equations》2003,19(5):555-570
This article presents and analyzes a simple method for the exterior Laplace equation through the coupling of finite and boundary element methods. The main novelty is the use of a smooth parametric artificial boundary where boundary elements fit without effort together with a straight approximate triangulation in the bounded area, with the coupling done only in nodes. A numerically integrated version of the algorithm is also analyzed. Finally, an isoparametric variant with higher order is proposed. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 555–570, 2003 相似文献
90.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Mikhail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5057-5066
The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007 相似文献