摘要:

AbstractA general and efficient procedure for microwave‐assisted reduction of liquid and solid ketones using sodium borohydride without solvents is described. The added support can enhance both the efficiency and chemoselectivity of reductio

ISSN:0009-4536    

DOI:10.1002/jccs.199900068

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractIn this paper previous results are compared for two different types of velocity mapping studies which probe vibrational energy disposal following the A‐band photodissociation of methyl iodide, CH3I + hv → CH3(v) + 1(2P3/2), 1*(2P1/2). Full three‐dimensional state‐specific speed and angular distributions of the nascent fragments have been recorded for the photoelectrons, iodine atoms, and methyl radicals, using state‐ and mass‐selective (2+1) resonance‐enhanced multi‐photon ionization (REMPI)/time‐of‐flight spectrometry. Two sources of information on the vibrational energy disposal are available from velocity mapping: (a) the photoelectron images, which give information on the initial stages of vibrational excitation in electronically excited CH3I, and (b) methyl radical images, which indicate the final energy disposal channels. Even though the two signals are believed to probe very different time‐scales of the dissociation process, good agreement between the two is found for the vibrational energy disposal trends. Several trends found in the data for methyl iodide photodissociation indicate that readjustment of theab initiomulti‐dimensional potential energy surfaces calculated for this molecu

ISSN:0009-4536    

DOI:10.1002/jccs.199900069

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractThe stability constants of several divalent first row transition and trivalent lanthanide metal complexes were determined by capillary electrophoresis (CE) methods. Four different approaches, i.e. direct formation, ligand exchange, metal exchange and metal‐ligand double exchange were developed. To verify if these CE methods are indeed applicable, the stability constant of CuHEDTA was re‐determined to be 17.47 ± 0.20 (consistent with the published 17.50) using the CuEDTA and ZnHEDTA metal‐ligand double exchange approach. The stability constants of lanthanide (Ce3+and Eu3+) and transition metal (Ni2+and Zn2+) complexes of an aminopolycarboxylate ligand, DO2A (1,7‐dicarboxymethyl‐1,4,7,10‐tetraazacyclododecane) were measured under the direct complex formation condition. The stability constant of the NiDO2A complex was determined by the ligand exchange method using 1,4,8,11‐tetraazaundecane (2,3,2‐tet) as the competing ligand. The stability constant of CuDO2A complex was determined by the metal exchange method using Zn2+ion as the competing metal ion, and complex formation competitions of Ni2+and Cu2+between DO2A and 2,3,2‐tet were studied by the metal‐ligand double exchange method. Effects of experimental conditions and the advantages and limitations of these CE m

ISSN:0009-4536    

DOI:10.1002/jccs.199900070

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractCoordination reactions ofN‐(2‐thienylmethylidene)aniline derivatives, L, with PdCl2or [PdCl4]2−in ethanol yield stable complexes of the typetrans‐(L)2PdCl2with the azomethine nitrogen atoms as σ donors. These are not readily convertible toothor‐palladated complexes. An X‐ray crystallographic study of the complex (L2)2PdCl2reveals a centrosymmetric geometry. The structure is in the triclinic space group\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm P}\bar 1 $\end{document}with a = 8.633(2) Å, b = 12.759(3) Å, c = 8.398(2) Å, α = 96.65(5)°, β = 111.47(5)*, γ= 101.28(6)°, and Z = 1. The final R factor is 0.043 (Rw = 0.044) for 2396 observed reflections. There is no real bonding between a thiophene sulfur atom and a central palladium ion. However, a long distance interaction between

ISSN:0009-4536    

DOI:10.1002/jccs.199900071

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractTreatment of [Et4N][Mo(CO)5(PPh2CS2)],1with unsaturated organic halides afforded the neutral complexes Mo(CO)5(PPh2CS2R) (R = CH2CN,2; R = CH2C≡CH,3). Alkylation reactions take place at the sulfur atom. Protonation of complex2and3with HBF4produced the intramolecular cyclization products [Mo(CO)5(PPh2CS2C2H3N)][BF4],4and [Mo(CO)5(PPh2CS2C3H4)][BF4],5, respectively. In complex4and5, two five‐membered 1,3‐dithiolium rings formed. Protonation of3to5is not reversible, but deprotonation of4byn‐BuLi or PPh3gave2quantitatively. Treatment of4withn‐Bu4NF yielded complex Mo(CO)5PPh2F,6and2with 1:1 ratio, but in the reaction of5andn‐Bu4NF only compound6was formed. All of these complexes are identified by spectrosco

ISSN:0009-4536    

DOI:10.1002/jccs.199900072

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractReactions of CH3OCH2CH2OH, PhOCH2CH2OH,o‐CH3OC6H4CH2OH, or PhSCH2CH2OH with Cp2ZrCl2in the presence of NEt3gave series monomeric complexes Cp2ZrClX (X = OCH2CH2OCH3(1), OCH2CH2OPh (2),o‐OCH2C6H4OCH3(3) or OCH2CH2SPh (4)). In a reaction of Cp2TiCl2with PhSCH2CH2OH in the presence of NEt3, the complex Cp2TiCl(OCH2CH2SPh) (5) was obtained. These complexes were characterized by the1H and13C NMR, and the chemical shifts of the Cp rings for complexes1–4are nearly identical, despite differences in ligands for an indication of similar structures of these complexes around the metal center. Complex4crystallizes into the monoclinic P21/c space group with a = 13.806(3) Å, b = 16.394(3) Å, c = 7.838(2) Å, β = 100.85(3)° Z = 4, R = 0.029, Rw= 0.044, and Gof = 1.19. The molecular structure of complex4shows that the 2‐(phenylthio)ethoxide bonds to the Zr metal center through the alkoxide donor leaving the thioether donor free from

ISSN:0009-4536    

DOI:10.1002/jccs.199900073

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractThe red complextrans‐Mo2(O2CCH3)2(μ‐dppa)2(BF4)2,1, was prepared by reaction of [Mo2(O2CCH3)2(CH3CN)6][BF4]2with dppa (dppa = Ph2PN(H)PPh2) in THF. The reactions of Mo2(O2C(CH2)nCH3)4with dppa and (CH3)3SiX (X = Cl or Br) afforded the complexestrans‐Mo2X2(O2C(CH2)nCH3)2(μ‐dppa)2(X = Cl, n = 2, 2; X = Br, n = 2, 3; X = Cl, n = 10,4; X = Cl, n = 12,5). Their UV‐vis, IR and31P{1H}‐NMR spectra have been recorded and the structures of1, 2and3have been determined. Crystal data for1: space group P21/n, a = 12.243(1) Å, b = 17.222(1) Å, c = 13.266(1) Å, β = 95.529(1)°, V = 2784.1(6) Å3, Z = 2, with final residuals R = 0.0509 and Rw = 0.0582. Crystal data for 24CH3Cl2: space group P21/n, a = 13.438(1) Å, b = 19.276(1) Å, c = 14.182(1) Å, β = 111.464(1)°, V = 3418.9(6) Å3, Z = 2, with final residuals R = 0.0492 and Rw = 0.0695. Crystal data for 3·4CH2Cl2: space group P21/n, a= 13.579(1) Å, b = 19.425(1) Å, c = 14.199(1) Å, β = 111.881(2)°, V = 3475.6(7) Å3, Z = 2, with final residuals R = 0.0703 and Rw = 0.0851. Comparison of the structural data shows that the effect of the axial ligand on weakening the Mo‐Mo bond strength is X−>CH3CN>BF4−. The Tmvalues are 121.7 °C for2, 11

ISSN:0009-4536    

DOI:10.1002/jccs.199900074

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractTwo bis(N,N‐dialkylamide) derivatives of DTPA [(carboxymethyl)iminobis (ethylenenitrilo) tetraacetic acid], DTPA‐BDMA = the bis(N,N‐dimethylamide) and DTPA‐BDEA = the bis(N,N‐diethylamide) were synthesized. Their protonation constants were determined by potentiometric titration in 0.10 M Me4NNO3and by NMR pH titration at 25.0 ± 0.1 °C. Stability and selectivity constants were measured to evaluate the possibility of using the corresponding gadolinium(III) complexes for magnetic resonance imaging contrast agents. The stability constants of gadolinium(III), copper(II), zinc(II), and calcium(II) complexes with DTPA‐BDMA and DTPA‐BDEA were investigated quantitatively by potentiometry. The stability constant for gadolinium(III) complexes is larger than those for Ca(II), Zn(II), and Cu(II) complexes. The selectivity constants and modified selectivity constants of the amides for Gd3+over endogenously available metal ions were calculated. Effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media is assessed by comparing pM values at physiological pH 7.4. Spin‐lattice relaxivity valuesR1for Gd(III) complexes were also determined. The observed relaxivity values were found to decrease with increasing pH in the acid range below pH 4 and relaxivity values became invariant with respect to pH changes over the range of 4–10.17O NMR shifts showed that the [Dy(DTPA‐BDMA)] and [Dy(DTPA‐BDEA)]complexes had one inner‐sphere water molecule. Water proton spin‐lattice relaxation rates for the [Gd(DTPA‐BDMA)] and [Gd(DTPA‐BDEA)]complexes were also consistent with one inner‐sphere gado

ISSN:0009-4536    

DOI:10.1002/jccs.199900075

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

Abstract2‐Benzoxazolethione reacts with the parent oxorhenium(V) complex, H2[ReOCl5], to yield either mononuclear or dinuclear complexes depending on the metal: ligand molar ratio and the concentration of hydrochloric acid containing the parent rhenium complex. The mononuclear complexs [ReOLCl(OH2)3]Cl2, [ReOL2(OH2)3]Cl3and [ReOLCl3(OH2)]; and dinuclear complexes [Re2O3(μ‐L)2Cl4]·2H2O and [Re2O2(μ‐L)L2Cl6]‐2H2O were obtained. Both types of complexes have octahedral configurations. The mononuclear complexes prepared in 6N HCl or in 9N HCl undergo irreversible one‐step solid‐phase thermochromism transformation, thus, the colour of complexes changed from green to brown, black or bluish‐green, upon heating. For the complexes obtained in 6N HCl, this step corresponds to structural changes due to the formation of other types of dinuclear complexes, while the mononuclear complex obtained in 9N HCl changes to another mononuclear complex with different coordination sites. On the other hand, the colour of the dinuclear complexes prepared in 2N HCl changed from brown to black, upon heating, in one step solid‐phase thermochromism transformation corresponding to a change in the mode of coordination sites of the organic ligand. All thermal products obtained have octahedral configurations. The ligand behaves in these complexes either as a neutral, mono‐, bidentate or monoanionic bidentate towards the oxorhenium ions. All complexes and the corresponding thermal products were isolated and their structures were elucidated by elemental analyses, conductance, IR and electronic absorption spectra, magnetic moments,1H NMR and TG‐DTA measurements as well a

ISSN:0009-4536    

DOI:10.1002/jccs.199900076

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY

摘要:

AbstractThe electrochemical behavior of the gold electrode modified by hybrid bilayer membranes in different concentrations of Fe(CN)63−/Fe(CN)64−was investigated by electrochemical impedance spectroscopy and cyclic voltammetry technology. The electron transfer between gold and the redox species separated by the hybrid bilayers assembly was completed by an electron tunneling process. A detailed equivalent circuit for electron transport across the HBMs is proposed. It was found that the apparent effective thickness of the hybrid bilayer membranes was lower than that of the sum of the chain length of octadecanethiol and phospholipid so some possible collapsed sites might exist at the hybrid bilayer membra

ISSN:0009-4536    

DOI:10.1002/jccs.199900077

出版商:WILEY‐VCH Verlag    

年代:1999

数据来源: WILEY