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Coordinated peroxide

D. Dolphin Such potentials refer to free hydrogen peroxide (H2O2). The potentials at which coordinated peroxide can be formed are lower, but subsequent protonation of such coordinated peroxide can result in the liberation of free peroxide which can then react with the periphery of the porphyrin. [Pg.110]

Secondly, there is an indication that metal(III)-peroxo side-on complexes are in general in equilibrium with corresponding metal(II)-superoxo end-on species. The position of such equilibrium could depend on various factors as structural and electronic properties of the porphyrin ligand, coordination of an axial ligand trans to peroxide/superoxide, solvent medium, temperature and involvement of coordinated peroxide/superoxide in possible hydrogen bonding or electrostatic interactions. These are interesting questions which should be addressed in future studies. [Pg.96]

It is noteworthy that the reaction of [Rh(dpf)2]+C104 (dpf = 6,6-diphenylfulvene) with 02 results in the formation of a coordinated peroxide by insertion of Oz between the two ligands (equation 56).208... [Pg.339]

The dioxygen complex shows oxygen transfer reactions characteristic of species containing coordinated peroxide (42), and, for example, we have isolated a sulfato complex from the reaction with S02 and a carbonato complex from a reaction with C02 in the presence of excess phosphine, and we have detected a peroxycarbonato species from the reaction with C02 (44). A reaction with H2 simply replaces the 02 to yield H2IrCl(PCy3)2, Complex 7 (44). [Pg.157]

Figure 12.7 (a) /u-rj2 rj2-Bridging mode of coordinated peroxide in oxyhaemocyanin, (b) X-ray... [Pg.826]

Other Complexes. Before we turn to a discussion of other complexes, it is worth making a few general comments about the biomimetic systems studied to date. The model systems are much slower ( 105-fold) than the enzyme (33). All peroxovanadium complexes, whether competent to catalyze bromide oxidation reactions or not, contain tj2-coordinated peroxide (4). Little is known about the binding of peroxide in the enzyme (see above), but one wonders whether the enhanced reactivity is derived from an alternative binding mode, such as end-on peroxide or hydroperoxide. The rapid enzymatic rate could also arise from the nature or configuration of the ligands to the vanadium ion. [Pg.345]

Two-electron reduction of dioxygen into coordinated peroxide can be easily performed by two metal centers undergoing concomitant one-electron oxidations, as shown in Equation 4.4 (Section 4.2.2). A variety of transition metal ions (cobalt, nickel, iron, manganese, copper, etc.) can form dinuclear peroxides. These complexes differ in structure (cA-p-1,2-peroxides, trans- l- 1,2-peroxides, p-r 2 r 2-peroxides), in stability and subsequent reactivity modes, and in the protonation state of the peroxo ligands (Figure 4.3). In certain cases, dinuclear p-r 2 r 2-peroxides and bis-p-oxo diamond core complexes interconvert, as discussed below for copper-dioxygen adducts. [Pg.144]

Similar electrophilic activation of coordinated peroxides or alkylperoxides can be observed for the metal ions in intermediate oxidation states. To give just one example, Sharpless epoxidation takes advantage of an electrophilic activation of alkyl hydroperoxides at titanium(IV). Notably, efficient epoxidation requires substrate binding in the vicinity of coordinated alkylperoxide, thus limiting the substrate scope of this reaction to allylic alcohols (alkoxy group acts as an anchor).1,45... [Pg.171]

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... [Pg.172]

As with enantioselective hydrogenation, we see that several factors are involved in the high efficacy of the Ti(OiPr)4-tartrate epoxidation catalysts. The metal ion has two essential functions. One is the assembly of the reactants, the allylic alcohol, and the hydroperoxide. The second is its Lewis acid character, which assists in the rupture of the 0—0 bond in the coordinated peroxide. In addition to providing the reactive oxidant, the r-butyl hydroperoxide contributes to enantioselectivity through its steric bulk. Finally, the tartrate ligands establish a chiral environment that leads to a preference for one of the diastereomeric TSs and results in enantioselectivity. [Pg.198]

Oxygen can be bound to metal ions with several geometries side-on (to form a triangle), end-on linear and end-on bent. The electronic possibiUties include a simple electron-pair donation from oxygen, 1-electron acceptance by oxygen so that there is effectively a coordinated superoxide ion and the charge on the metal is increased one unit (M O2 M 02") and 2-electron acceptance to give effectively coordinated peroxide with the oxidation state of the metal increased by two (M Oj M - 0 )... [Pg.265]

Mechanism of Iron-Coordinated Peroxide 0-0 Bond Cleavage as Shown by Products and Stoichiometries... [Pg.152]

The primary focus of research using transition metal phosphine complexes for oxidations is in the complexation and activation of molecular oxygen. These oxygen complexes have been variously regarded as complexes of coordinated peroxide, superoxide, or singlet oxygen, and their reactivity with reduced substrate has been interpreted on such a basis. In this chapter, we will focus on the chemical reactivity of these compounds for oxygen atom transfer oxidation reactions, with a particular emphasis on the mechanistic features of these processes. [Pg.378]


See other pages where Coordinated peroxide is mentioned: [Pg.232]    [Pg.13]    [Pg.112]    [Pg.331]    [Pg.72]    [Pg.127]    [Pg.128]    [Pg.129]    [Pg.25]    [Pg.58]    [Pg.126]    [Pg.289]    [Pg.340]    [Pg.148]    [Pg.188]    [Pg.47]    [Pg.4227]    [Pg.658]    [Pg.481]    [Pg.127]    [Pg.128]    [Pg.674]    [Pg.146]    [Pg.171]    [Pg.172]    [Pg.179]    [Pg.195]    [Pg.683]    [Pg.154]    [Pg.156]    [Pg.138]    [Pg.4226]    [Pg.365]    [Pg.64]   
See also in sourсe #XX -- [ Pg.365 ]




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