Hydroperoxo complexes oxidation

The activity of haloperoxidase and halogenase in the oxidation of halide ion reveals that Fe(lll)-hydroperoxo complexes oxidize halide ions via oxygen atom transfer while the corresponding Fe(lV)-oxo complex reacts via electron transfer. ... 

Keywords EXAFS H2O2 Hydroperoxo complexes IR Raman Partial oxidations Peroxo complexes TitanosUicate TS-1 UV-Vis XANES... 

Transition metal peroxides, particularly peroxo (2), alkylperoxo (7) and hydroperoxo (8) complexes, are extremely important reactive intermediates in catalytic oxidations involving molecular oxygen, hydrogen peroxide and alkyl hydroperoxides as the oxygen source. Representative peroxo complexes are listed in Table 3, and alkylperoxo and hydroperoxo complexes are listed in Table 4 together with their reactivities. 

Electrophilic activation of coordinated peroxides can be achieved by protonation, which typically yields end-on coordinated hydroperoxides.16 For example, the well-defined hydroperoxo complexes of rhodium and chromium efficiently oxidize inorganic substrates such as halide anions these reactions are acid catalyzed.16 Hydroperoxo intermediates were implicated in some enzymatic oxidations, such as hydroxylation catalyzed by cytochrome P450 (Figure 4.32). Although significant... 

Two additional intermediates, the ferric peroxy anion and ferric hydroperoxo complex, have been proposed to substitute for the ferryl as the actual oxidizing species in at least some P450 reactions. The role of the ferric peroxy anion in some reactions is supported by good evidence and is discussed in the section on carbon-carbon bond cleavage reactions (see Section 8), but the proposed role of the ferric hydroperoxide in electrophilic double bond and heteroatom oxidations is discussed here. 

The cxurent interest in the ferric hydroperoxo complex as a P450-oxidizing species derives largely from the work by Vaz et ai, who observed that mutation of the conserved threonine (Thr303) in CYP2E1 to an alanine decreased the allylic hydrox-ylation of cyclohexene, cts-2-butene, and tmns-2-butene, but increased the epoxidation of the same... 

Figure 6.2. Hypothetical ipso-substitution mechanism involving the ferric hydroperoxo complex and ferryl species as the potential oxidizing species. ...

The well-known rhodium (136) and iridium 137) peroxo complexes (PhgPlaRhCKOa) (40), [(PhgPlaRhCKOalJa (41), and (Ph3P)2(C0)IrCl(02) (42) have been investigated for their reactivity with acetylacetone, acacH 138). Only the former complex, 40, exhibited any reactivity (in the presence of two equivalents of triphenylphosphine), yielding the hydroperoxo complex (43), (see Scheme 8). Complex 43 reacts with PPhg to form triphenylphosphine oxide, but does not react with any active methylene compounds (methyl acetoacetate, diethyl malonate, or acetone) save for cyclopentadiene. In the last instance, a poorly characterized, unstable system tentatively formulated as 44 may have been formed. In refluxing benzene, 43 did react with excess acacH to form the bis(acac) complex 45. 

Some of these activated species like HO Cu -hydroperoxo, or Cu -hydroxo have been also proposed in the case of the oxidations of the DNA nucleobases (55). Various mechanisms like HO addition on a double-bound, hydrogen abstraction on the methyl groups or electron transfer induce nucleobases oxidations and copper complexes are oxidant enough to perform them, but, in the presence of excess of reductants, such as in the conditions often used during DNA oxidation by copper complexes, oxidized nucleobases (base radicals and radical cations) may be reduced back to undamaged species. Thus the ability of copper complexes to oxidize nucleobases could be underestimated. 

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