Dioxygen formation

The principal mechanistic events include N-N bond formation stage, where the coordinated NO reactant is transformed into the NzO semi-product via dinitrosyl ( M-(NO)2]Z) or dinitrogen dioxide ( M-N202 Z) intermediates, depending on the nature of TMI (vide infra). Simultaneously, the primary (M Z active sites are converted into the secondary [M-0]Z active sites involved in the dioxygen formation cycle [5], The mononitrosyl complexes are usually postulated to be the key intermediate species of this step [2,5,41], whereas the mechanistic role of dinitrosyls and dinitrogen dioxide is more indistinct as yet. 

Nuclearity 4, oxidation chemistry of dioxygen formation (4 electrons)... 

Interactions with Dioxygen. Formation of a 1 1 diamagnetic adduct at low temperatures in HMPA solutions of [Co(pc)(4-Mepy)] (pc = phthalocyanine 4-Mepy =... 

The peroxide and superoxide species, which naturally tend to accumulate, are prone to very slow reactions of disproportionation (reactions (7), (8)) (< 1 I moM s" ). These reactions are also the cause of the secondary dioxygen formation (always less compared to H2), that occurs at long time. Among these reactions, specially the three following can be listed, the last one (mixed type) being a basic equivalent of the Haber-Weiss reaction ... 

The derivation of the rate expression based on this model can be approached in two equivalent ways, but to initiate either one, the rate must first be defined. In this case it is either that of ozone disappearance or that of dioxygen formation, noting from equation 1 that... 

Figure 3.13 Specific rates of (a) and (b) gaseous dioxygen formation...

SAMs on Copper. Like its congeners, copper also adsorbs alkanethiols that form oriented SAMs attached to the surface as thiolates (75). These samples are especially difficult to obtain in high quality, and the samples that we have examined always contained copper(I) oxide. We find this system to be extremely sensitive to the details of preparation, particularly the extent of exposure of the metal film to dioxygen (formation of a thick copper oxide) or to solution (formation of copper sulfi ). Optimization of the procedure produced high-quality samples with PIERS spectra indistinguishable from those obtained on SAMs on silver (75). The structure of the SAMs on copper is, therefore, probably the same as that on silver The axis of the trans-extend hydrocarbon chain is oriented close to the surface normal. Since the SAMs we characterized formed on an oxidized suiface, we are hesitant to make claims... 

With higher alkenes, three kinds of products, namely alkenyl acetates, allylic acetates and dioxygenated products are obtained[142]. The reaction of propylene gives two propenyl acetates (119 and 120) and allyl acetate (121) by the nucleophilic substitution and allylic oxidation. The chemoselective formation of allyl acetate takes place by the gas-phase reaction with the supported Pd(II) and Cu(II) catalyst. Allyl acetate (121) is produced commercially by this method[143]. Methallyl acetate (122) and 2-methylene-1,3-diacetoxypropane (123) are obtained in good yields by the gas-phase oxidation of isobutylene with the supported Pd catalyst[144]. 

Reversible formation of a dioxygen complex by direct reaction of O2 with trani-[Ir(CO)Cl(PPh3)2] discovered by L. Vaska. 

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. ... 

The possibility of a radical mechanism is supported by the observation of the accelerating effect of molecular oxygen on the cyclopropanation. Miyano et al. discovered that the addition of dioxygen accelerated the formation of the zinc carbenoid in the Furukawa procedure [24a, b]. The rate of this process was monitored by changes in the concentration of ethyl iodide, the by-product of reagent formation. Comparison of the reaction rate in the presence of oxygen with that in the... 

Scheme 10.27 Catalytic cycle of HppE. Dashed arrows indicate electron transport. In this scheme HPP binds to iron1". After a one-electron reduction, dioxygen binds and reoxidizes the iron center. The peroxide radical is capable of stereospecifically abstracting the (pro-R) hydrogen. Another one-electron reduction is required to reduce one peroxide oxygen to water. Epoxide formation is mediated by the resulting ironlv-oxo species.

Formation and stabilities of cobalt dioxygen complexes in aqueous solution. A. E. Martell, Acc. Chem. Res., 1982,15,155-162 (68). 

A number of investigations of the copper-group oxides and dioxygen complexes have been reported. The electronic spectra of CuO, AgO, and AuO were recorded in rare-gas matrices (9), and it was found that the three oxides could be formed effectively by cocondensation of the metal atoms with a dilute, oxygen matrix, followed by near-ultraviolet excitation. The effective wavelengths for CuO or AgO formation were X > 300 nm and for AuO was X > 200 nm. In addition, the laser fluorescence spectrum of CuO in solid Ar has been recorded (97). 

Partenheimer showed (ref. 15) that when toluene was subjected to dioxygen in acetic acid no reaction occurred, even at 205 °C and 27 bar. He also showed that when a solution of cobalt(II) acetate in acetic acid at 113 °C was treated with dioxygen ca. 1 % of the cobalt was converted to the trivalent state. In the presence of a substituted toluene two reactions are possible formation of a benzyl radical via one-electron oxidation of the substrate or decarboxylation of the acetate ligand (Fig. 9). Unfortunately, at the temperatures required for a reasonable rate of ArCH3 oxidation (> 130 °C) competing decarboxylation predominates. As noted earlier, two methods have been devised to circumvent this undesirable... 

Caris-Veyrat, C. et al., Cleavage products of lycopene produced by in vitro oxidations characterization and mechanisms of formation, J. Agric. Food Chem., 51, 7318, 2003. Caris-Veyrat, C. et al., Mild oxidative cleavage of beta, beta-carotene by dioxygen induced by a ruthenium porphyrin catalyst characterization of products and of some possible intermediates, New J. Chem., 25, 203, 2001. 

The removal of angular methyl groups is important in the transformation of steroids and related compounds. In these reactions, the methyl group is oxidized to the aldehyde before fission in which the carbonyl group oxygen is retained in formate (or acetate), and one oxygen atom from dioxygen... 

FIGURE 3.21 (a) Degradation of 1,2-dimethylbenzene by dioxygenation and elimination with formation of... 

After dioxygenation and the formation of catechols, ring hssion is mediated by a different group of dioxygenases. 

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