Vanadium peroxo complexes

Alkoxo monoperoxo vanadium complexes are also efficient radical oxidants of the alcoholic function again with a radical chain mechanism whose details are indicated in Scheme 16 in the case of 2-propanol. Similar radical peroxo species have been indi- ... 

Shul pin and coworkers have demonstrated, in several papers, that other peroxo vanadium complexes closely related to 36, containing in the coordination sphere amino acids, nitrogen-containing bases or weak carboxylic acids, are effective oxidants of satnrated and aromatic hydrocarbons. An accnrate account containing this work, together with results related to the use of other transition metals, has appeared and aU the relevant literature can be found there. 

Covalent vanadium(V)-peroxo complexes of general formula VCHC XpicJLjLj (L1,L2 = H20 or basic ligands) and ionic complexes with the formula [V0(02)(pic)2] A+(A+ = H+, PPh4+) can easily be synthesized from V20S,H202, picolinic acid and ligands. These complexes exhibit a different behavior from that of Mo - and Wvi-peroxo complexes.22... 

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. 

Conte, V., F. Di Furia, and S. Moro. 1994. 51V NMR investigation on the formation of peroxo vanadium complexes in aqueous solution Some novel observations. J. Mol. Catal. 94 323-333. 

Shaver, A., J.B. Ng, D.A. Hall, B. Soo Lum, and B.I. Posner. 1993. Insulin-mimetic peroxo vanadium complexes Preparation and structure of potassium oxodiper-oxo(pyridine-2-carboxylato)vanadate(V), K2[V0(02)2(C5H4NC00)]-2H20, and potassium oxodiperoxo(3-hydroxypyridine-2-carboxylato)vanadate(V), K2[V0(02)2 (0HC4H3NC00)]3H20, and their reactions with cysteine. Inorg. Chem. 32 3109-3113. 

Schwendt, P., A. Oravcova, J. Tyrselova, and F. Pavelcik. 1996. The first tetranuclear vanadium)V) peroxo complex Preparation, vibrational spectra and x-ray crystal structure of K7[V204(02)8(P04)] 9H20. Polyhedron 15 4507 4511. 

Kaliva, M., T. Giannadaki, A. Salifoglou, C.P. Raptopoulou, A. Terzis, and V. Tangou-lis. 2001. pH-dependent investigations of vanadium(V)-peroxo-malate complexes from aqueous solutions. In search of biologically relevant vanadium(V)-peroxo species. Inorg. Chem. 40 3711-3718. 

Clague, M.J. and A. Butler. 1995. On the mechanism of cw-dioxovanadium(V)-catalyzed oxidation of bromide by hydrogen peroxide Evidence for a reactive, binu-clear vanadium(V) peroxo complex. J. Am. Chem. Soc. 117 3475-3484. 

Kwong DWJ, Chan OY, Wong RNS, Musser SM, Vaca L. DNA-photocleavage activities of vanadium(V)-peroxo complexes. Inorg Chem 1997 36 1276-77. 

Kwong DWJ, Chan C-K, Shek LK, Wong RNS. Effects of supercoiling on the sequence-specific photo-modification of DNA by a vanadium(V)-peroxo complex. J Inorg Biochem 2005 99 2062-73. 

Binuclear vanadium(V) peroxo complexes such as (NH4)5[V202(02)4P04]-H20 are also known.30 They have been implicated as the reactive species in the bromide oxidation by hydrogen peroxide,31 a process which is important in some biological systems (Section 17-B-8). Some stable peroxo compounds display insulin-mimetic activity both in vivo and in vitro.32... 

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). ... 

Labeling studies have clearly shown that the active catalyst is not a peroxo compound but an alkyl peroxide in which the alkyl peroxide group is probably 0,0-triangularly bonded to the metal,as illustrated by the X-ray crystal structure of the vanadium complex (22). The well-characterized d" metal 0,N-bonded N,JV-dialkylhydroxylamino complexes (79), (80) and (81) might be reminiscent of the alkyl peroxide complexes of Mo " , V " and Ti ", which are difiBcult to isolate and involved as reactive intermediates in reactions (64) or (65). 

Peroxo examples formed by the direct reaction with molecular dioxygen in the first row of the transition metals are few. One of the first examples of a peroxo vanadium complex formed by the direct reaction with dioxygen is a Tp Pr-bound seven-coordinate pentagonal-bipyramidal Vv complex Tp PrV0(f72-02)(pz PrH), with a relatively short O—O distance of 1.379(6) A and relatively high O—O stretching frequency of 960 cm-1, relative to typical peroxo species.14 First-row transition metalloproteins which bond molecular dioxygen are discussed, with their models, in Volume 8. 

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. 

A few years later, Hubert Mimoun discovered the rather selective oxidation of benzene by a few vanadium(V) peroxo complexes [10], Using an excess of hydrogen peroxide under phase-transfer conditions transformed this stoichiometric reaction into a true catalytic process, but the turnover numbers remained very low [11]. 

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