Oxovanadium

As the scheme indicates, the blue vanadyl oxovanadium cation can be (quantitatively) oxidised to vanadium(V) and the latter is reduced... 

In the higher oxidation states partially hydrolysed species dominate the aqueous chemistry, the most important being the oxovanadium(IV), or vanadyl, ion This gives the sul-... 

Similarly, treatment of the corresponding oxovanadium(IV) complex of 4 with refluxing acetic anhydride for 3 hours yields the corresponding acetylated oxovanadium(IV) complex of 5 in 89% yield.- 6... 

Oxovanadium(IV) 6,I5,24,33-Tetraphenyl-l,10,19,28-tetraaza-2r3-naphthalocyanine (3) Single Procedure 4 ... 

Spin-spin coupling in oxovanadium complexes. A. Syamal, Coord. Chem. Rev., 1975, 16, 309-339... 

ESR spectra, 2, 511 Oxovanadium(V) complexes aqueous solution, 3,1026 Oxyanions coordinated... 

The modified Sharpless reagent was also successfully applied288 for the asymmetric oxidation of a series of 1,3-dithiolanes 248 to their S-monooxides 249 (equation 134). It was observed that the optical induction on sulphur (e.e. from 68 to 83%) is not significantly affected by the substituents R1 and R2. Asymmetric oxidation of a few aryl methyl sulphides by organic hydroperoxides in the presence of a catalytic amount of the optically active Schiff base-oxovanadium(IV) complexes gave the corresponding sulphoxides with e.e. lower than 40%289. 

Schiff base-oxovanadium(IV) complexes, as optically active oxidizing agents 291... 

The feasibility of synthesizing oxovanadium phthalocyanine (VOPc) from vanadium oxide, dicyanobenzene, and ethylene ycol using the microwave synthesis was investigated by comparing reaction temperatures under the microwave irradiations with the same factors of conventional synthesis. The efficiency of microwave synthesis over the conventional synthesis was illustrated by the yield of crude VOPc. Polymorph of VOPc was obtained ttough the acid-treatment and recrystallization step. The VOPos synthesized in various conditions were characterized hy the means of an X-ray dif actometry (XRD), a scanning electron microscopy (SEM), and a transmission electron Microscopy (TEM). 

Recently mononuclear ruthenium(II) and binuclear ruthenium(III) complexes of 5 and its iV-phenyl derivative have been isolated [214], Although many of the complexes were not soluble in the culture medium, both ruthenium(II) and ruthenium(III) complexes showed considerably more activity against E. coli than the uncomplexed thiosemicarbazones. Similar results were found for the oxovanadium(IV) complexes of the same ligands [VO(L)2Br]Br, where L is the deprotonated 2-formylpyridine N-phenylthiosemicarbazone, was the most potent inhibitory activity [215]. 

The structure of the hexanuclear oxovanadium(IV) anion [(VO)6(CO)4(OH)9]5 (86) is highly reminiscent of the structure of the P4Mo6Eg anions with four C03 groups replacing the four phosphato groups. The connecting scheme is of type 5. The nine oxo bridges are protonated. 

Reeder and Rieger6 used ESR spectra to identify complex ions and to estimate formation constants for aqueous oxovanadium(iv) complexes with lactic acid, thiolactic acid, glycolic acid, and thioglycolic acid. Through the use of second-harmonic detection, which produces second-derivative spectra, the resolution was good enough that several of the individual species could be separately... 

K. Fukui, Y. Fujisawa, H. Ohya-Nishiguchi, H. Kamada and H. Sakurai, In vivo coordination structural changes of a potent insulin-mimetic agent, bis(picolinato)oxovanadium(IV), studied by electron spin-echo modulation spectroscopy, J. Inorg. Biochem., 1999, 77, 215. 

The ring-opening of the cyclopropane nitrosourea 233 with silver trifiate followed by stereospecific [4 + 2] cycloaddition yields 234 [129]. (Scheme 93) Oxovanadium(V) compounds, VO(OR)X2, are revealed to be Lewis acids with one-electron oxidation capability. These properties permit versatile oxidative transformations of carbonyl and organosilicon compounds as exemplified by ring-opening oxygenation of cyclic ketones [130], dehydrogenative aroma-tization of 2-eyclohexen-l-ones [131], allylic oxidation of oc,/ -unsaturated carbonyl compounds [132], decarboxylative oxidation of a-amino acids [133], oxidative desilylation of silyl enol ethers [134], allylic silanes, and benzylic silanes [135]. 

Addition of alkyllithium to cyclobutanones and transmetallation with VO(OEt)Cl2 is considered to give a similar alkoxide intermediates, which are converted to either the y-chloroketones 239 or the olefinic ketone 240 depending on the substituent of cyclobutanones. Deprotonation of the cationic species, formed by further oxidation of the radical intermediate, leads to 240. The oxovanadium compound also induces tandem nucleophilic addition of silyl enol ethers and oxidative ring-opening transformation to produce 6-chloro-l,3-diketones and 2-tetrahydrofurylidene ketones. (Scheme 95)... 

A recently disclosed transformation describes an interesting oxovanadium(v)-induced vicinal dialkylation of cyclic enones by dialkylzincs.317 The method is based on the previous finding of the same authors that oxidation of... 

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