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Sealed Tube (sealed + tube)
Selected AbstractsSodium Bis(trimethylsilyl)amide in the Oxidative Conversion of Aldehydes to NitrilesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2006Jih Ru Hwu Abstract The feasibility of the Me3Si species acting as a nucleofuge was investigated in compounds containing the NSiMe3 moiety. Treatment of various aromatic aldehydes with 2.2 equiv. of NaN(SiMe3)2 at 185 °C in a sealed tube produced the corresponding nitriles in high yields (81,98,%). In these reactions, NaN(SiMe3)2 acted as an oxidizing agent. Results from control experiments indicate that the Me3Si unit can depart efficiently from the NSiMe3 moiety of N -silylimine intermediates. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] A comparison of a microfocus X-ray source and a conventional sealed tube for crystal structure determinationJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2009Thomas Schulz Experiments are described in which a direct comparison was made between a conventional 2,kW water-cooled sealed-tube X-ray source and a 30,W air-cooled microfocus source with focusing multilayer optics, using the same goniometer, detector, radiation (Mo,K,), crystals and software. The beam characteristics of the two sources were analyzed and the quality of the resulting data sets compared. The Incoatec Microfocus Source (IµS) gave a narrow approximately Gaussian-shaped primary beam profile, whereas the Bruker AXS sealed-tube source, equipped with a graphite monochromator and a monocapillary collimator, had a broader beam with an approximate intensity plateau. Both sources were mounted on the same Bruker D8 goniometer with a SMART APEX II CCD detector and Bruker Kryoflex low-temperature device. Switching between sources simply required changing the software zero setting of the 2, circle and could be performed in a few minutes, so it was possible to use the same crystal for both sources without changing its temperature or orientation. A representative cross section of compounds (organic, organometallic and salt) with and without heavy atoms was investigated. For each compound, two data sets, one from a small and one from a large crystal, were collected using each source. In another experiment, the data quality was compared for crystals of the same compound that had been chosen so that they had dimensions similar to the width of the beam. The data were processed and the structures refined using standard Bruker and SHELX software. The experiments show that the IµS gives superior data for small crystals whereas the diffracted intensities were comparable for the large crystals. Appropriate scaling is particularly important for the IµS data. [source] On the precision and accuracy of structural analysis of light-induced metastable statesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2007Vincent Legrand Bragg diffraction data were collected on single crystals of the spin-crossover complex [Fe(phen)2(NCS)2] in its low-spin and light-induced metastable high-spin states. Experimental variables included the temperature (32 and 15,K), the X-ray source (sealed tube and synchrotron), and the time interval between laser light excitation of the sample (, = 647,nm). From a comparison of the structural parameters refined, it is shown that photo-crystallographic measurements suffer significantly and systematically from bias if the probed sample contains residual ground-state species, resulting from an incomplete photo-conversion or a significant metastable- to ground-state relaxation. It follows that a 4% population of species in a different spin state affects the Fe,N bond lengths by more than three standard deviations, and the FeN6 polyhedron volume by as much as seven standard deviations, while the mean atomic position misfit exceeds 0.005,Å. [source] Metal-Free and PdII -Promoted [2+3] Cycloadditions of a Cyclic Nitrone to Phthalonitriles: Syntheses of Oxadiazolines as well as Phthalamide,PdII and Dihydropyrrolyl-iminoisoindolinone,PdII Complexes with High Catalytic Activity in Suzuki,Miyaura Cross-Coupling ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 30 2008Jamal Lasri Dr. Abstract The previously unknown reactions between phthalonitriles, 1,2-(CN)2(C6)R1R2R3R41 (1,a, R1=R2=R3=R4=H; 1,b, R1=R2=R4=H, R3=CH3; 1,c, R1=R4=H, R2=R3=Cl; 1,d, R1=R2=R3=R4=Cl; 1,e, R1=R2=R3=R4=F), and a cyclic nitrone, ,O+NCHCH2CH2CMe22, proceed under heating in a sealed tube to give phthalimides 3, 2-oxadiazolyl-benzonitriles 4 or ortho -bis(oxadiazolyl)tetrafluorobenzene 4,e,. In the presence of palladium(II) chloride, phthalonitriles 1 react with 2 at room temperature, to give bis(pyrrolidin-2-ylidene)phthalamide PdII complexes 5 via metal-promoted rupture of the NO bond of the oxadiazoline ring. The ketoimine ligands thus generated can be liberated from the metal by displacement with a diphosphine. Although the first [2+3] cycloaddition of 2 to 1 can occur in the absence of the metal to give the mono-cycloadducts 4, the second [2+3] coupling at the still-unreacted cyano group requires its activation by coordination to PdII, affording complexes 6 containing two ligated oxadiazolyl-benzonitriles. These ligands undergo either i) further cycloaddition with 2 to afford ultimately (upon rearrangement) the bis(pyrrolidinylidene)phthalamide complexes 5 or ii) NO bond cleavage in the oxadiazoline ring with intramolecular attack of the imine nitrogen on the cyano carbon and bridging to a second PdII center to afford dimeric palladium(II) complexes 7, with chloride bridges, that bear a dihydropyrrolyl-iminoisoindolinone, a new type of ligand. The compounds were characterized by IR, 1H, and 13C,NMR spectroscopy, ESI MS or FAB+ MS, elemental analyses and, in the case of 4,c, 5,a, 5,c, and 7,c, also by X-ray diffraction analysis. Complexes 5,a and 7,c show high catalytic activity for the Suzuki,Miyaura cross-coupling reaction of bromobenzene and phenylboronic acid and give biphenyl in high yields with turnover frequencies (TOFs) of up to 9.0×105,h,1. [source] In Situ Synthesis of Trisubstituted Methanol Ligands and Their Potential as One-Pot Generators of Cubane-like Metal ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2006Brendan F. Abrahams Dr. Abstract Two different one pot routes to a variety of metal cubane compounds are reported; one route is based on an in situ benzilic acid type rearrangement and the other involves in situ nucleophilic attack at a ketone. Diketosuccinic acid in basic solution in the presence of certain divalent metal ions undergoes a benzilic acid type rearrangement to generate the carbon oxyanion, C(CO2,)3O,, which serves as a cubane-forming bridging ligand in a series of octanuclear complexes of composition [M8{C(CO2)3O}4](H2O)12 (M=Mg, Mn, Fe, Co, Ni, Zn). At the heart of each of these highly symmetrical aggregates is an M4O4 cubane core, each oxygen component of which is provided by the alkoxo centre of a C(CO2,)3O, ligand. Reaction of 2,2,-pyridil, (2-C5H4N)COCO(2-C5H4N), and calcium nitrate in basic alcoholic solution, which proceeds by a similar benzilic acid type rearrangement, gives the cubane compounds, [Ca4L4(NO3)4] in which L=(2-C5H4N)2C(COOR)O, (R=Me or Et). Nucleophilic attack by bisulfite ion at the carbonyl carbon atom of 2,2,-dipyridyl ketone in the presence of certain divalent metals generates the electrically neutral complexes, [{(C5H4N)2SO3C(OH)}2M] (M=Mn, Fe, Co, Ni, Zn and Cd). Cubane-like complexes [M4{(C5H4N)2SO3C(O)}4] (M=Zn, Mn) can be obtained directly from 2,2,-dipyridyl ketone in one-pot reaction systems (sealed tube, 120,°C) if a base as weak as acetate ion is present to deprotonate the OH group of the initial [(C5H4N)2SO3C(OH)], bisulfite addition compound; the [(C5H4N)2SO3C(O)]2, ligand in this case plays the same cubane-forming role as the ligands C(COO,)3O, and (2-C5H4N)2C(COOR)O, above. When excess sodium sulfite is used in similar one-pot reaction mixtures, the monoanionic complexes, [M3Na{(C5H4N)2SO3C(O)}4], (M=Zn, Mn, Co) with an M3NaO4 cubane core, are formed directly from 2,2,-dipyridyl ketone. [source] | ||||||||||