Peroxo complexes formation

Funahashi, S., K. Haraguchi, and M. Tanaka. 1977. Reactions of hydrogen peroxide with metal complexes. 2. Kinetic studies on the peroxo complex formation of nitrilo-triacetatodioxovanadate(V) and dioxo(2,6-pyridinedicarboxylato)vanadate(V). Inorg. Chem. 16 1349-1353. 

Time-resolved spectroscopy (stopped-flow ultraviolet-visible (UV-vis) spectroscopy at -90° C, proprionitrile or acetonitrile, [O2] S> [complex]) has been used to characterize intermediates and evaluate the mechanism of the peroxo complex formation (see Fig. 16) (196). Based on the similarity of the spectral features with known superoxo copper(lI) and peroxo-dicop-per(ll) complexes (262, 268, 281) the mechanism shown in Scheme 17 was proposed, and the spectra of the superoxo copper(II) and peroxo-dicop-per(II) complexes were determined (see Table XI). For steric reasons and in... 

The colour sequence already described, for the reduction of van-adium(V) to vanadium(II) by zinc and acid, gives a very characteristic test for vanadium. Addition of a few drops of hydrogen peroxide to a vanadate V) gives a red colour (formation of a peroxo-complex) (cf. titanium, which gives an orange-yellow colour). 

Figure 14.5 (a) Reaction of Al,Al -ethylenebis(3-Bu -salicylideniminato)cobalt(II) with dioxygen and pyridine to form the superoxo complex [Co(3-Bu Salen)2(02)py] the py ligand is almost coplanar with the Co-O-O plane, the angle between the two being 18°.< (b) Reversible formation of the peroxo complex [Ir(C0)Cl(02)(PPh3)2]. The more densely shaded part of the complex is accurately coplanar. ... 

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... 

Concerning peroxo complexes, it is worth noticing that they can be formed in TS-1 by evolution of both or rf- hydroperoxo complexes upon a further deprotonation in presence ofwater with formation of H30 /H20. Very recently Bonino et al. [49] have shown, by titration in aqueous medium with NaOH, that the acidity of the TS-1/H2O system is remarkably increased by addition of H2O2 (compare full squares with full circles in Fig. 8), a feature not observed for the Ti-free silicalite-1 system (open circles and squares in Fig. 8). 

Formation of the side-on peroxo complex by interaction of H2O2/H2O... 

In a similar fashion, the homoleptic complex [Pd(ITmt) ] lb readily reacts with O2 to form the corresponding peroxo-complex 2b (Scheme 10.1). This complex, npon exposure to CO, leads to the peroxo-carbonate complex 3b [10]. Under the same reaction conditions, the formation of 3a does not occur, presumably due to the larger steric hindrance of the Mes ligand. 

CoCl(PPh3)3], Reaction of [Co(TIMEN )]Cl 9 with oxygen in the presence of NaBPh leads to the formation of the peroxo-complex [Co(r -02)(TIMEN 5 )] BPh 10, which is a rare example of a side-on r -peroxo cobalt complex (the majority of Co-O -adducts are rj -O -complexes, i.e. end-on). The authors also showed that 10 is capable of converting molecular oxygen to benzoylchloride. 

Fig. 4. Substrate first binds to the complete system containing all three protein components. Addition of NADH next effects two-electron reduction of the hydroxylase from the oxidized Fe(III)Fe(III) to the fully reduced Fe(II)Fe(II) form, bypassing the inactive Fe(II)Fe(III) state. The fully reduced hydroxylase then reacts with dioxygen in a two-electron step to form the first known intermediate, a diiron(III) peroxo complex. The possibility that this species itself is sufficiently activated to carry out the hydroxylation reaction for some substrates cannot be ruled out. The peroxo intermediate is then converted to Q as shown in Fig. 3. Substrate reacts with Q, and product is released with concomitant formation of the diiron(III) form of the hydroxylase, which enters another cycle in the catalysis.

I know of no definitive evidence concerning the formation of a p-peroxo complex between a3 and CuB, and if the analogy between cytochrome oxidase and the other heme proteins, I have referred to, holds then I see no need to suggest such peroxo-bridging. 

Sajus et al. [243,244] synthesized the peroxo complex of molybdenum(VI) and studied its reaction with a series of olefins. This peroxo complex M0O5 was proved to react with olefins with epoxide formation. The selectivity of the reaction increases with a decrease in the complex concentration. It was found to be as much as 95% at epoxidation of cyclohexene by M0O3 in a concentration 0.06 mol L-1 at 288 K in dichloroethylene [244], The rate of the reaction was found to be... 

Some evidence to suggest that peroxo complexes can be intermediates in the oxidation of Pt(II) by 02 has been presented. As shown in Scheme 41, a Pt(IV) peroxo complex was obtained by reacting cis-PtCl2(DMSO)2 and 1,4,7-triazacyclononane (tacn) in ethanol in the presence of air (200). An alkylperoxoplatinum(IV) complex is obtained in the reaction of (phen)PtMe2 (phen = 1,10-phenanthroline) with dioxygen and isopropyl-iodide. Under conditions that favor radical formation (light or radical initiators), an isopropylperoxoplatinum(IV) compound was obtained (201,202), depicted in Scheme 42. 

The kinetic models for these reactions postulate fast complex-formation equilibria between the HA- form of ascorbic acid and the catalysts. The noted difference in the rate laws was rationalized by considering that some of the coordination sites remain unoccupied in the [Ru(HA)C12] complex. Thus, 02 can form a p-peroxo bridge between two monomer complexes [C12(HA)Ru-0-0-Ru(HA)C12]. The rate determining step is probably the decomposition of this species in an overall four-electron transfer process into A and H202. Again, this model does not postulate any change in the formal oxidation state of the catalyst during the reaction. 

These findings for Re peroxo complexes are in striking contrast with Ti and V catalyzed reactions [41, 51, 52, 111, 113] in which the metal-alcoholate bond drives the allylic OH directivity. We recall that the formation of alcoholate intermediates was also rejected for epoxidations of allylic alcohols with Mo and W peroxo compounds while H-bonding (between OH and the reacting peroxo fragment) was considered consistent with kinetic data for these complexes [115]. 

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