Peroxo complex dimers

The aqueous solution chemistry of Tc(VII) is dominated by the stability of the TeO anion [4], Nitrido complexes are few and are limited to peroxides and one dimeric nitrido-hydrazido example. The peroxo complexes based on the [TcVIIN(02 )2] core are analogous to the well-known isoelectronic [MoviO(02)2] complexes [117] and are the only examples of nitridoperoxo complexes and rare examples of peroxo complexes of a metal in the +7 oxidation state. 

Ir(III) and Rh(III) peroxo complexes, species 3, may be obtained by reaction of 2 or O2 with Ir(I) and Rh(I) thiolato complexes (equation 5). An analogous reaction was observed also with a dimeric Rh(I) species and singlet oxygen that produces (equation 6). 

Cobalt(II) porphyrins bind dioxygen as would be expected by analogy with the wealth of cobalt(II) complexes which display this property. The initial addition product is invariably a superoxo-type species, confirmed by ESR, IR and X-ray studies.154 Subsequent reaction of the oxygenated complex with more Co11 porphyrin leads to a peroxo-bridged dimer. No X-ray data are available for cobalt porphyrin peroxo-bridged dimers but the formation of such dimers is well established in cobalt chemistry. 

In light of the accepted mechanism for cytochrome P-450 (97-100), a superoxo-Cu(II) intermediate is further reduced, leading to dioxygen activation. Accordingly, a monomeric peroxo or hydroperoxo copper(II) complex serves as a synthetic model for these intermediates of copper-containing monooxygenases. However, no well-characterized complexes of these types are available to date. Formation of a monomeric hydroperoxo or acylperoxo complex was reported to occur when a trans-/u-l,2-peroxo complex, [(Cu(TPA))2(02)]z+, was treated with H+ or RC(O)+, but no details of the structures and properties of the complexes were provided (101). A related complex, a monomeric acylperoxo cop-per(II) complex, was synthesized (102). Low-temperature reaction of a dimeric copper(II) hydroxide complex, [Cu(HB(3,5-iPr2pz)3)]2(OH)2, with 2 equivalents of m-CPBA (3-chloroperoxybenzoic acid) yielded a monomeric acylperoxo complex whose structure was characterized by... 

Table 57 Structures Monomeric and Dimeric Cobalt(III)-Peroxo Complexes...

The /u-peroxo dimer intermediate, C, in the oxidation of four-coordinate Fe porphyrins to the PFe-O FeP /U.-OXO dimer via equations (23A-C) (cf. Scheme 2) of tetrakis(m-tolyl)porphrnatoiron(III), has been detected by NMR spectroscopy at low temperatures. The /r-peroxo complex has a larger isotropic shift (16 vs. 13 ppm for the ii-0x0 dimer at -50 °C) for the pyrrole-H at all temperatures, and has an antiferromagnetic coupling constant, —27, that is about 30% smaller than that for the /r-oxo dimer, E the magnetic moment decreases from 2.6/tb at —50°C to about 2.2/tb at —80°C, both consistent with weaker antiferromagnetic coupling in the /u-peroxo complex. ... 

While the li-tl rri -peroxo complex is a hypothetical structure, the difference in energy favoring the bis( X-oxo) isomer was estimated to be 30 kcal/mol. Finally, the dissociation of thebis( l-oxo) dimer into two terminal oxo complexes (i.e. TpCo=0, see eq.l) is prohibited by a large energy difference (ca. 75 kcal/mol). 

Figure 10 Reactions of phenolates with fi-rj. rj -peroxo complex (7) yields an orf/ o-hydroxylation reaction reminiscent of Tyr, while reactions of phenols by both (7) and bis-/x-oxo complex (8) results in ortho-phenol coupled dimers through an apparent PCET pathway...

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