Manganese peroxo complexes

The first mononuclear manganese(III) peroxo species without a porphyrin ligand, [Mn(3,5-Pr 2pzH)(HB(3,5-Pr 2pz)3)(02)] (144),was prepared from the reaction of [ Mn"(HB(3,5-Pr 2pz)3) 2](OH)2 with excess of H2O2 (10-20 equivalents) in the presence of 3,5-Pr 2pzH (2 equivalents) at room temperature. It is a six-coordinate complex with a side-on peroxo group. 

Although no X-ray crystal structure determination of 9 is available, the structure of a related manganese species, [peroxo(tetraphenylporphyrinato)]man-ganese(lll) [K(K222)][MnTPPP(02>], complex 10, has recently been reported by Valentine and co-workers (42) by the two-step reaction of Mn TPP(Cl) with 2 equivalents of KO2 [Eq. (6)]. 

Catalytic oxidations using manganese complexes and dioxygen or peroxide oxidants are rather rare. Although reversible dioxygen adducts of the superoxo or peroxo type have been detected in the interaction of manganese(II)-pophyrin or -Schiff base complexes with O2 at low tem-... 

The structure of the active component, manganese pyrophosphate, has been reported in the literature (24). It is layer like with planes of octahedrally coordinated Hn ions being separated by planes of pyrophosphate anions (P20y ). Examination of models of this compound gave calculated Hn-Hn thru space distances of 3.26 and 3.45 angstroms, a metal-metal distance close to that found for binuclear dibridged peroxo- and superoxo- complexes of cobalt ( ). 

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... 

Although manganese dioxygen complexes are probably involved in many enzymatic reactions, few such complexes have been structurally characterized— manganese(III) species include side-on ( jj2-02)Mn(porph), a /i3-oxo,ju,-peroxo-... 

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. 

III.B.2), complexes with manganese, chromium, as well as second- and third-row transition metal ions (e.g., ruthenium) oxidation reactions with dioxygen alone or with other peroxides (e.g., ferf-butyl-peroxide) the stabilization and spectroscopic characterization of mononuclear superoxo, peroxo, and oxo complexes other catalytic processes (e.g., the iron-catalyzed aziridination), enantioselective reactions with chiral bispidine ligands and the iron oxidation chemistry continues to produce novel and exciting results. 

T. thermophilus MnSOD, and the data showed that there were three phases to this reaction a fast burst phase of quick HO2 dismutation, a slower second phase, and a final fast phase (78). A dead-end form of the enzyme was implicated to account for the slow phase (78). This has been formulated as a side-on-bound Mn -peroxo species based on spectroscopic similarities to manganese model complexes with side-on-bound peroxy groups (83). Such phases are not observed for FeSOD (84). 

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