56 resultados para OXOVANADIUM(IV)
Resumo:
Bis(p-substituted benzoylmethyl)tellurium dibromides, (p-YC6H4COCH2)2TeBr2, (y=H (1a), Me (1b), MeO (1c)) can be prepared
either by direct insertion of elemental Te across CRf-Br bonds (where CRf refers to α-carbon of a functionalized organic moiety) or by the oxidative addition of bromine to (p-YC6H4COCH2)2Te (y = H (2a), Me (2b), MeO (2c)). Bis(p-substituted benzoylmethyl)tellurium dichlorides, (p-YC6H4COCH2)2TeCh (y = H (3a), Me (3b), MeO (3c)), are prepared by the reaction of the bis(p-substituted benzoylmethyl)tellurides 2a--c with S02Cl2, whereas the corresponding diiodides (p-YC6H4COCH2)2Teh (y = H
(4a), Me (4b), MeO (4c)) can be obtained by the metathetical reaction of la--c with KI, or alternatively, by the oxidative addition of
iodine to 2a--c. The reaction of 2a--c with allyl bromide affords the diorganotellurium dibrornides la--c, rather than the expected
triorganotelluronium bromides. Compounds 1-4 were characterized by elemental analyses, IR spectroscopy, 1H, l3C and 125Te
NMR spectroscopy (solution and solid-state) and in case of Ie also by X-ray crystallography. (p-MeOC6H4COCH2)2TeBr2 (1c) provides, a rare example, among organotellurium compounds, of a supramolecular architecture, where C-H-O hydrogen bonds appear to be the non-covalent intermolecular associative force that dominates the crystal packing.
Resumo:
The synthesis and characterization of unsymmetric diorganotellurium compounds containing a sterically demanding I-naphthyl or
mesitylligand and a small bite chelating organic ligand capable of 1,4-Te···N(O) intramolecular interaction is described. The reaction
of ArTeCl3 (Ar = I-ClOH7, Np; 2,4,6-Me3C6H2' Mes) with (SB)HgCI [SB = the Schiff base, 2-(4,4'-N02C6H4CH=NC6H3-Me)] or a methyl ketone (RCOCH3) afforded the corresponding dichlorides (SB)ArTeCI2 (Ar = Np, 1Aa; Mes, 1Ba) or (RCOCH2)ArTeCl2 (Ar = Np; R = Ph (2Aa), Me (3Aa), Np (4Aa); Ar = Mes, R = Ph (2Ba)). Reduction of 1Aa and 1Ba by Na2S205 readily gave the tellurides (SB)ArTe (Ar = Np (1A), Mes, (1B) but that of dichlorides derived from methylketones was complicated due to partial decomposition to tellurium powder and diarylditelluride (Ar2Te2), resulting in poor yields of the corresponding tellurides 2A, 2B and 3A. Oxidation of the isolated tellurides with S02Cl2, Br2 and I2 yielded the corresponding dihalides. All the synthesized compounds have been characterized with the help of IR, 1H, l3C, and 125Te NMR and in the case of 2Aa, and 2Ba by X-ray crystallography. Appearance of only one 125Te signal indicated that the unsymmetric derivatives were stable to disproportionation to symmetric species. Intramolecular 1,4-Te· . ·0 secondary bonding interactions (SBIs) are exhibited in the crystal structures of both the tellurium(IV) dichlorides, 2Aa, and 2Ba. Steric repulsion of the mesityl group in the latter dominates over lone pair-bond pair repulsion, resulting in significant widening of the equatorial C-Te-C angle. This appears to be responsible for the lack of Te· . ·CI involved supramolecular associations in the crystal structure of 2Ba.
Resumo:
Two of the most commonly used classifications in IS research are the factor approach and the process approach. While many studies of IS implementation are undertaken using a factor approach, little research so far examines the process of e-commerce implementation, especially in relation to the implementation of e-commerce in business-to-business (B2B) relationships. A holistic understanding of implementation which combines both the factor and process approaches using a case study method, is suggested as particularly suitable because of its ability to capture the reality of e-commerce implementation in an organisation's natural environment and in much greater detail than is possible using one of these approaches alone. In this paper, therefore, we endeavour to contribute to what we perceive as a gap in the body of theory surrounding the implementation process in the business-to-business e-commerce literature. We describe the findings of multiple case studies involving ten major Australian e-commerce initiators. In addition to confirming our earlier finding of the importance of non-technical factors for the success of the implementation process we also present, through our case studies, the various management and business issues associated with the success or failure of B2B e-commerce implementation.
Resumo:
Obesity is a worldwide problem, not just an issue for industrialized nations. Therefore, we need to examine opportunities for prevention and treatment from a global perspective.
Resumo:
Although potassium permanganate [Mn(VII)] has been used extensively as a chemiluminescence reagent for many decades, other manganese-based oxidants have only recently been explored for this purpose. There is strong evidence to suggest that, like permanganate, manganese(III) and manganese(IV) oxidants react with many molecules to produce an excited manganese(II) species that emits light. However, these reagents differ markedly in terms of selectivity, and possess characteristics that provide new avenues for detection, such as the immobilisation of solid manganese dioxide, the production of ‘soluble’ manganese(IV) nanoparticles, and the electrochemical generation of manganese(III). In this review we examine the emergence of these alternative manganese oxidants as chemiluminescence reagents.
Resumo:
Electrophilic substitution of acylmethanes (methyl ketones), RCOCH3 (R = i-Pr, 1; Et, 2; Me, 3) with aryltellurium trichlorides, ArTeCl3 (Ar = 1-C10H7, Np, A; 2,4,6-Me3C6H2, Mes, B; 4-MeOC6H4, Anisyl, C) under mild conditions affords the corresponding acylmethyl(aryl)tellurium dichlorides (RCOCH2)ArTeCl2. Reduction of the dichlorides, gives tellurides, (i-PrCOCH2)ArTe, 1A–1C, which give the corresponding dihalides, (i-PrCOCH2)ArTeX2 (X = Cl, 1Aa–1Ca; Br, 1Ab–1Cb; I, 1Ac–1Cc) when reacted in situ with SO2Cl2, Br2 or I2. The unsymmetric tellurides are labile towards disproportionation and attempts to obtain them lead to the isolation of Ar2Te2 except in the case of (i-PrCOCH2)MesTe ( 1B), which represents an interesting example of a kinetically stable aryl(alkyl)telluride. All the dihalomesityltellurium(IV) derivatives show separate 1H and 13C NMR signals for the ortho methyls irrespective of the sizes of R and X ligands. The telluride, 1B with free rotation about Te–C(mesityl) bond shows, like the unsymmetric diorganotellurium(IV) dihalides, only one 125Te NMR signal. The 1,4-chelating behavior of the acyl ligand among diorganotellurium(IV) compounds is inferred from the X-ray diffraction data for 1Aa, 1Ac, 1Ba, 1Bb, 1Ca and 1Cc which are indicative of the presence of intramolecular TeO secondary bonding interactions (SBIs) at least in the solid state. As a consequence, steric repulsion in case of the mesityltellurium(IV) derivatives, 1Ba and 1Bb, reaches the threshold so as to cause loss of two-fold rotational symmetry of the mesityl group about the Te–C(mesityl) bond axis. Intermolecular C–HO H-bonding interactions appears to stabilize such an orientation of the aryl ligand at least in the solid state.