Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
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103,026 records were found.
In search of new possibilities for rendering catalysts soluble in fluorous solvents, the preparation of a sodium derivative of tetrakis{3, 5-bis(perfluorohexyl)phenyl}borate, a new and highly fluorous anion, is described. This weakly coordinating anion exhibits substantial affinity for perfluorinated solvents and is therefore expected to make a broad range of cationic transition-metal catalysts compatible with fluorous biphasic recycling techniques.
Reaction of 3, 5-bis[(dimethylamino)methyl]phenyl iodide with 3,5-bis[(dimethylamino)methyl]phenylacetylene in diethylamine in the presence of bis(triphenylphosphine)palladium(II) dichloride (3.6 mol%) and copper(I) iodide (3.0 mol%) gave 1,2-(bis(3,5-bis[(dimethylamino)methyl]phenyl)acetylene (1) in 82% yield. The palladium catalyst was recovered in 93% yield as trans-(3,5-bis[(dimethylamino)methyl]phenyl)bis(triphenylphosphine)palladium (II) iodide (2). The crystal structure of 2 shows that the coordination geometry of the palladium is distorted square-planar. No inter- or intramolecular interactions between the N-donor atoms and the Pd are observed.
The potentially C,N,N'-chelating anionic aryldiamine ligand [C6H4(CH2N(Me)CH2CH2NMe2)-2]- (CNN) has been employed in the preparation of six-coordinate Ta(V) alkylidene complexes. The new dichloro alkylidene complex [TaCl2(=CH-t-Bu)(CNN)], 2, prepared from [TaCl3(=CH-t-Bu)(THF)2] and [Li(CNN)]2, 1, has been obtained as a mixture of three diastereoisomers (2a-c) in 51% yield. The molecular structure of the major isomer 2a, determined by X-ray methods, shows this to be a tetragonal bipyramidal complex in which the metal coordination sphere is comprised of the C,N,N' facially bonded CNN, two cis-positioned chlorides in the equatorial plane, and a neopentylidene group and the NMe2 nitrogen donor mutually trans-positioned at the apices. The dialkoxide complexes [Ta(=CHR)(CNN)(O-t-Bu)2] (R = t-Bu (3a), CMe2Ph (3b)) have been obtained by trans...
The sulfidation of @c-alumina- and titania-supported(cobalt)molybdenum oxide catalysts has been studied with X-rayabsorption spectroscopy and temperature programmed sulfidation (TPS).The catalysts were stepwise sulfided at temperatures between 298 and673 K and their structure was determined with EXAFS spectroscopy. Onalumina oxygen-sulfur exchange starts at a temperature just aboveroom temperature resulting in the formation of monomeric and dimericmolybdenum sulfide species containing disulfide ligands. Between 448and 523 K the disulfide ligands are reduced with hydrogen and onlydimeric molybdenum sulfide species with a Mo-Mo distance of 2.77 Aremain. Above 523 K these dimers aggregate to larger MoS{2}particles.In contrast, on titania molybdenum oxide is sulfided to yieldisolated molybdenum sulfide monomers at 523 K, which similarlyagg...
The dioxygenation rate in reactions catalyzed by lipoxygenase- 1 from soybeans has been measured
as a function of the enzyme present in the Fe(II1) form with rapid kinetic techniques. The experiments
were carried out at pH 10, 25 'C. The product concentration and the fraction of iron(II1) lipoxygenase
were monitored by measuring the absorbance at 243 nm and the tryptophan fluorescenceat 330 nm (excitation
at 287 nm), respectively. In reactions started with 1.3 mu M iron(I1) lipoxygenase and 9 mu M linoleate, the
initial rate, Qnit (estimated from the increase in absorbance over the initial 0.02 s of the reaction), is very
small (4 SKI). In contrast, when the reactions are started with 1.3 mu M iron(II1) lipoxygenase, Qnit is large
(1 50 s-l). In reactions started with mixtures of iron(I1) and iron(II1) lipoxygenase, finit is linearly r...
