Oxygen adducts

Recent developments in the studies of molecular oxygen adducts of cobalt(II) compounds and related systems. T. D. Smith and J. R. Pilbrow, Coord. Chem. Rev., 1981, 39, 295-383 (337). 

Molecular complexes and oxygen adducts of tetrapvrrole pigments. J. H. Fuhrhop, Angew. Chem., Int. Ed. Engl., 1976, 15, 648-659 (76). 

Recent developments in the studies of titanium and vanadium porphyrins with special emphasis on oxygen adducts, low valent metalloporphyrins and related systems of sulphur and selenium. R. Gui-lard and C. Lecomte, Coord. Chem. Rev., 1985, 65, 87 (76). 

The fast interaction of O2 with Fe(II)-cysteine complexes to give an oxygen adduct which rapidly undergoes one-electron breakdown to an Fe(III)-cysteine complex and -OJ has been examined by stopped-flow spectrophotometry at 570 nm . Subsequent decomposition of the Fe(IlI) complex to yield Fe(II) and the disulphide, cystine, was much slower. Both mono- and bis-complexes of Fe(Il) are involved and the reaction is first-order in both Fe(II) complex and O2 k (mono) = (5 +1) x 10 l.mole ksec" and k (bis) = (2 0.5) x lO l.mole . sec at 25 °C, corresponding to factors of 10 and 10 times faster than the analogous reactions with sulphosalicylic acid complexes of Fe(II), a feature attributed to Fe(ll)-S bonding in the cysteine complexes. ... 

Trialkylboranes, especially triethylborane, are used in conjunction with 02 to generate radicals.297 The alkyl radicals are generated by breakdown of a borane-oxygen adduct. An advantage this method has over many other radical initiation systems is that it proceeds at low temperature, e.g., -78°C. 

The rate of the Ir(III) catalyzed reaction was found to be first-order in [Ir] and [H2DTBC], but independent of 02 concentration in chloroform (56). The mechanism proposed for the reaction (Scheme 4) postulates that the protonation of the hydroperoxo a-oxygen by the hydroxy group of the bonded catechol in Int 1 leads to the formation of H202. The o-qui-none ligand of Int 2 is replaced by the partially coordinated catechol in the next step. In order to comply with the experimental rate law, the rate-determining step needs to be the reaction of the oxygen adduct (B) with catechol. 

As with an isolated double bond, epoxide formation in an aromatic ring, i.e., arene oxide formation, can occur mechanistically either by a concerted addition of oxene to form the arene oxide in a single step, pathway 1, or by a stepwise process, pathway 2 (Fig. 4.78). The stepwise process, pathway 2, would involve the initial addition of enzyme-bound Fe03+ to a specific carbon to form a tetrahedral intermediate, electron transfer from the aryl group to heme to form a carbonium ion adjacent to the oxygen adduct followed by... 

DR. ENDICOTT In fact, the cobalt-eyelam-oxygen adduct can have a very short lifetime depending on the competition reactions. If the cobalt dioxygen adduct is generated in the presence of greater concentrations of CoAA([l4]aneN ), the intermediate lifetime is clearly shortened. The classical studies made by Ralph Wilkins, for instance, were carried out under conditions in which intermediates only achieved small stationary state concentrations. 

The kinetics of the reaction between [V(salen)] in pyridine and oxygen have been determined and interpreted in terms of the formation of a [V(salen)] -oxygen adduct. This reinforces the view that vanadium(iii) complexes can act as oxygen carriers. The oxidation of the 1,2-cyclohexanediaminetetra-acetic acid complex of V " has been studied in solutions of pH 6—12. ... 

Molecular oxygen adducts. Despite many physical studies, the bond length of co-ordinated oxygen can still be interpreted as either superoxide (or peroxide) ion, or an electronically excited state of molecular oxygen. In order to establish the bond character more clearly, a n.m.r. study has been carried out on several complexes, including [Rh(02)(Ph2PC2H4PPh2)]Cl. Unfortunately, no resonance attributable to O2 could be found, suggesting that Vaska type complexes tumble at a rate which broadens the resonances beyond... 

Mel, I2, or CI2). Except for the oxygen adduct, the X—Y bonds have been broken in all these complexes. The data suggest a loss of electron density on Ir along the series from XY = Hj to CI2, which is consistent with the relative powers of H and Cl as a-donors. °... 

Since Fenton s work in the late nineteenth century, the role of transition metals in oxygen chemistry is known, but the formation of oxygen adducts with coordination metal complexes and their importance for O2 activation have been studied much later [1, 97]. The lively interest in ORR catalysis comes from its utmost importance to the development of fuel cells and this justifies that only a few studies have been done with metal complexes in solution most have been devoted to carbon electrodes modified by immobilization of a catalyst. The research for good catalysts that could be efficient substitutes for the expensive platinum naturally moved toward porphyrins. 

Since di-te/7-butylsulfide delivers the sulfoxide in the photosensitized reaction and no a-hydroxysulfides were observed from the other sulfides of Table XIV, the photosensitized oxidation of sulfides (and probably also that of sulfoxides) takes another course than in the thermal reaction. It was suggested that singlet oxygen (formulated as the sensitizer-oxygen adduct -Sens-CV278,280) reacts with a sulfide to give a highly reactive sulfo-peroxide intermediate, 431, which immediately reacts with another sulfide molecule to yield two stable sulfoxide molecules. 

EPR Parameters of Radiation-Induced Centers in NHtY and Their Oxygen Adducts... 

Pretreatment temperature (CC) Primary center g tensor (27AI) (G) Oxygen adduct ... 

Hi. Zeolites exchanged with transition metal ions. In the first row, scandium-, titanium-, cobalt-, and nickel-exchanged zeolites have been the most studied. Cobalt-exchanged zeolites are discussed in Section IV,E since they lead to oxygen adducts on adsorption of oxygen. There are several cases where copper and particularly iron ions are found as impurity cations which affect the oxygen adsorption properties of the zeolite. 

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