Hydroxylation vanadium-peroxo complexes

Mimoun, H., L. Saussine, E. Daire, M. Postel, J. Fischer, and R. Weiss. 1983. Vanadium(V) peroxo complexes. New versatile biomimetic reagents for epoxidation of olefins and hydroxylation of alkanes and aromatic hydrocarbons. J. Am. Chem. Soc. 105 3101-3110. 

The mechanism of oxygen transfer from the peroxide (29) to the substrate still remains a matter of controversy. Current opinions favor the formation of a high-valent FeO (or Fe =0 or Fe —0-) (30) active species, which acts as a homolytic hydrogen abstractor from the substrate. An alternative mechanism considers the Fe -peroxide complex as the actual hydroxylating reagent, by analogy with the reactivity of vanadium(V)-peroxo and -alkylperoxo complexes and that of chromium(Vl)-peroxo complexes (see below). ... 

Aromatic hydrocarbons can be oxidized to the corresponding phenols by transition metal peroxo complexes and, in particular, vanadium(V) peroxo complexes, which act either as electrophilic oxygen transfer reagents or as radical oxidants -, depending on the nature of the ligands coordinated to the metal and on the experimental conditions. Vanadium picolinato peroxo complex (V0(02)PIC(H20)2) (39) (PIC = picoUnic acid anion) has been reported to be particularly effective in the hydroxylation of benzene and substituted benzenes (equation 50) . Accordingly, 39 smoothly oxidizes substituted benzenes 38 to the corresponding monophenols 40 in acetonitrile at room temperature. 

Many hydroxylated linalools [including compounds 105, 106, 108, and 110, both (Z)- and ( )-isomers], as well as the epoxides of both furanoid (109) and pyranoid (see section on pyrans) linalyl oxides, have been identified in papaya fruit (Carica papaya). At the same time, the first reported occurrence of die two linalool epoxides (112) in nature was made. These epoxides are well known to be unstable and easily cyclized (see Vol. 2, p. 165) and have been made by careful peracid oxidation of linalool. An interesting new method has now been described. While the vanadium- or titanium-catalyzed epoxidation of geraniol (25) gave the 2,3-epoxide (see above), as does molybdenum-catalyzed epoxidation with hydrogen peroxide, the epoxidation of linalool (28) with molybdenum or tungsten peroxo complexes and hydrogen peroxide led, by reaction on the 6,7-double bond, to 112. ... 

DNA cleavage as the mechanism by which tumour growth is inhibited is also been suggested for the action of bis(peroxo)vanadium(V) complexes of the general composition [V0(02)2L] (L = o-phenanthroline or bipyridyl) and traced back to the formation of hydroxyl radicals. 

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