Peroxo complexes catalytic activity

Immediately upon addition of the urea-hydrogen peroxide adduct to the solution containing methyltrioxorhenium, a yellow color develops due to formation of the catalytically active rhenium peroxo complexes.3... 

In the same spirit DFT studies on peroxo-complexes in titanosilicalite-1 catalyst were performed [3]. This topic was selected since Ti-containing porous silicates exhibited excellent catalytic activities in the oxidation of various organic compounds in the presence of hydrogen peroxide under mild conditions. Catalytic reactions include epoxidation of alkenes, oxidation of alkanes, alcohols, amines, hydroxylation of aromatics, and ammoximation of ketones. The studies comprised detailed analysis of the activated adsorption of hydrogen peroxide with... 

Katsuki and coworkers reported that Zr(salen)-based derivatives served as efficient catalysts for asymmetric BV reactions using UHP as terminal oxidant . Complex 117 in chlorobenzene at 0 °C showed the best catalytic activity with enantiomeric excesses higher than 80%, in most cases. Similarly to what was proposed for Ti(salen) derivatives (equation 51), the treatment of Zr(salen) complexes with H2O2 would give a Zr-peroxo (salen) complex 118, prone to ring-opening with formation of a Criegee adduct 119 and evolution to products (equation 81). 

Titanium(IV)-porphyrin [TiO(TPP)] as well as molybdenum(V)-porphyrin [MoO(OMe)(TPP)] complexes were found to be active for the catalytic epoxidation of alkenes by alkyl hydroperoxides, whereas their peroxo derivatives are inactive.632 Iron(III)-porphyrin-peroxo complexes such as Fe(TPP)02NMe4 did not react with hydrocarbons, but form sulfato complexes upon reaction with S02.632 Manganese(III)-porphyrin-peroxo complexes Mn(02)(TPP) K+ were recently characterized by X-ray crystallography.634... 

The catalytic dismutation of superoxide is actually more complicated in E. coli [42] and B. thermophilus [43] Mn-SODs than that of either Cu or Fe proteins since it may involve an inactive form of the enzyme. The inactive form is believed [44] to contain a Mnm-side-on peroxo unit (of the type shown in Figure 29) formed within the hydrophobic environment of MnSOD, in the absence of H+, by the oxidative addition of the superoxide ion to the Mn11 center. When H+ ions are present, an active, end-on peroxo complex forms, yielding successively a bound hydroperoxide ion and free dihydrogen peroxide (cf. Figure 3). Thus, the key parameter that turns the reaction off or on may be the absence or presence of a H+ ion [44],... 

Studies of the oxidation of organic sulfides with amino acid-derived ligands in acetonitrile revealed very little difference between the mechanism of their oxidation and that of halides, except for one major exception. Despite the fact that acid conditions are still required for the catalytic cycle, hydroxide or an equivalent is not produced in the catalytic cycle, so no proton is consumed [48], As a consequence, there is no requirement for maintenance of acid levels during a catalyzed reaction. Peroxo complexes of vanadium are well known to be potent insulin-mimetic compounds [49,50], Their efficacy arises, at least in part, from an oxidative mechanism that enhances insulin receptor activity, and possibly the activity of other protein tyrosine kinases activity [51]. With peroxovanadates, this is an irreversible function. Apparently, there is no direct effect on the function of the kinase, but rather there is inhibition of protein tyrosine phosphatase activity. The phosphatase regulates kinase activity by dephosphorylating the kinase. Oxidation of an active site thiol in the phosphatase prevents this down-regulation of kinase activity. Presumably, this sulfide oxidation proceeds by the process outlined above. 

Finally, a mention should be made about the one peroxo system which will become more and more dominant the organometallic oxides of rhenium(VII). Such compounds have been found to be of outstanding catalytic activity for a number of oxygen transfer reactions with hydrogen peroxide.92 The best studied complex is methyltrioxorhenium(VII) (MTO) and its congeners. Figure 2.32 illustrates its synthesis. Epoxidation, aromatic oxidation and halide oxidation with these complexes have been studied with hydrogen peroxide and shown to be remarkably efficacious. 

ReMe(NAr)20 reacts rapidly with P(OMe)3 to form OP(OMe)3 and ReMe(NAr)2 P(OMe)3 2 (73). More basic phosphines react very slowly but replace P(OMe)3 in (73). Interestingly, (73) under O2 rapidly forms ReMe(NAr)20 and 0P(0R)3. This catalytic reaction is proposed to take place via the peroxo complex (74) that unveils the activation of molecular O2 by a ReMe(NAr)2 fragment. A parallel activation of O2 with MTO is, however, less efficient. ... 

Catalytic Activity of Some Vanadium Peroxo Complexes Structural Properties of Vanadium Peroxo Complexes Vanadium in Mushrooms Vanadium in Coal... 

I. Catalytic Activity of Some Vanadium Peroxo Complexes... 

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