Vanadium complexes iodide

Compound (l,3,5-Me3CgH3)V(CO)3 was proposed as an intermediate in the reaction shown in Eq. (11) but was not isolated. Treatment of compound [(l,3,S-Me3CgH3)2V][V(CO)g] with Lil in tetrahydrofuran (THE) precipitated the cation as the iodide salt. Both the neutral and cationic bisarene vanadium complexes are paramagnetic having 1 and 2 unpaired electrons, respectively 131). 

It would be of considerable interest to see whether vanadium-peroxo complexes are also able to oxidize bromide and display kinetic behavior similar to that of the vanadium-containing bromoperoxidases. In this respect the complexes reported by Li et al. (80) may provide a useful contribution. Conversely, some attention should be paid to whether bromoperoxidases show specificity only toward bromide or iodide. These enzymes may perhaps be tuned to catalyze the oxidation and oxygenation of other nucleophiles. 

The manganate ion is not reduced by bromide ion but is reduced slowly by iodide ion and quickly by vanadyl(IV) or hexacyano-ferrate(II) ions. When the latter two ions are used as reductants, especially with the potassium complex, green products are obtained rapidly and in high yield. The green species is unstable in solution and is apparently in equilibrium with the reactants. With potassium salts, the solubility of the product is low, and the reaction is driven to completion. Potentiometric titrations show that a one-electron reduction occurs to produce the green species, which has been characterized by analysis and optical and e.s.r. spectroscopy. It is a mixed-valence species similar to the heteropoly blues of molybdenum and tungsten. E.s.r. spectra suggest that the extra electron is fairly well trapped on a specific vanadium atom, and the complex is therefore a class II mixed-valence species.8... 

Methylbromoarsines, synthesis 26 Vanadium(III) fluoride, synthesis 27 Sulfur(IV) fluoride, synthesis 33 Peroxydisulfuryl difluoride, synthesis 34 Trichloro(tripyridine)chromium(III), synthesis 36 Tris(3-bromoacetylacetonato)chromium(III), synthesis 37 Trichloro(tripyridine)molybdenum(III), synthesis 39 Uranyl chloride 1-hydrate, synthesis 41 Rhenium(III) iodide, synthesis 50 Potassium hexachlororhenate(IV) and potassium hexa-bromorhenate(IV), synthesis 51 Iron-labeled cyclopentadienyl iron complexes, synthesis 54 Inner complexes of cobalt(III) with diethylenetriamine, synthesis 56... 

The mechanism of reaction (Scheme 5) involves the proton equilibrium of vanadium(v), followed by reaction with the hydrated form of the a-keto-acid. The values K=3A (35 °C) and 2.0 (30 °C) have been derived kinetically. Initial oxidation of glyoxylic acid to oxalic acid is ruled out in view of the complex reaction of the latter with V. A study has been made, however, of the oxalic acid catalysis of the oxidation of iodide by vanadium(v). ... 

The natural products gutta-percha and balata consist of tra w-l,4-polyisoprene. With the aid of vanadium trichloride and triethylalumium, tra w-l,4-polyisoprene can be produced with 98% trans-, A enchainments [133,258]. The optimal Al/V ratio is the range of 5 to 7. The activity can be increased by the addition of small amounts of ether, heterogenerization on supports (kaolin, Ti02), or blending with titanium(III) chloride or titanium alcoholates [259-261]. Further catalysts featuring lower activity, however, are allylnickel iodide, trisallylchormium on silica, or complexes of neodymium [262 265]. 

The first term is the law observed in the absence of catalyst. The effect is dramatic, however, with associated rate constants ko and ki being 50.3 1 mol s and 3.43 x 10 1 mol s respectively, and may be ascribed to the formation of a Mo -BrOa" complex with no evidence for any change in the oxidation state of the catalyst during the course of the reaction. The kinetics and mechanism of the bromate-ascorbic acid reaction have also been reported, and the effects of phosphate on the oxidation of iodide by chlorate in the presence of catalytic concentrations of vanadium(iv) have been described, the latter systems being considered to involve vanadium(iv)-phosphate complexes. 

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