Oxygen atom transference

N—Fe(IV)Por complexes. Oxo iron(IV) porphyrin cation radical complexes, [O—Fe(IV)Por ], are important intermediates in oxygen atom transfer reactions. Compound I of the enzymes catalase and peroxidase have this formulation, as does the active intermediate in the catalytic cycle of cytochrome P Q. Similar intermediates are invoked in the extensively investigated hydroxylations and epoxidations of hydrocarbon substrates cataly2ed by iron porphyrins in the presence of such oxidizing agents as iodosylbenzene, NaOCl, peroxides, and air. 

The most important thionyl compound is OSCI2 — it is readily prepared by chlorination of SO2 with PCI5 or, on an industrial scale, by oxygen-atom transfer from SO3 to SCI2 ... 

Nickel(IV) complexes react with dimethyl sulphoxide in acidic solution to give the sulphone and nickel(II) ions. The kinetics of this reaction have been studied and found to be very complex in nature. The reaction probably proceeds by initial complexation of the dimethyl sulphoxide to the nickel(IV) species followed by electron transfer and oxygen atom transfer producing the observed products149. 

Within each group relatively simple molecules will be discussed first. In some cases a given substrate may be reduced by modes (i) and (ii) depending on the reductant and in other cases the mechanism is unknown, for example the reduction of perchlorate ion may involve either electron-acceptance or oxygen atom transfer. 

Among the transfer and exchange of non-metals, the reactions of atomic oxygen, O, at low potential are unusual in that transport is not required. H20 carries O everywhere but it is not by itself active in O-incorporation into carbon frameworks. It is observed that fixed Mo (W) coenzymes have always been used as catalysts in the oxygen atom transfer from H20 to aldehydes reversibly. 

Holm, R.H. (1990). The biological relevant oxygen atom transfer of molybdenum. Coordin. Chem. 

The organic substrates in Chart 8 can be divided into two main categories in which (i) the oxidation of olefins, sulfides, and selenides involves oxygen atom transfer to yield epoxides, sulfoxides, and selenoxides, respectively, whereas (ii) the oxidation of hydroquinones and quinone dioximes formally involves loss of two electrons and two protons to yield quinones and dinitrosobenzenes, respectively. In order to provide a unifying mechanistic theme for the seemingly disparate transformations in Chart 8, we note that nitrogen dioxide exists in equilibrium with its dimeric forms, namely, the predominant N—N bonded dimer 02N—N02 and the minor N—O bonded isomer ONO—N02 (equation 88). 

The oxidation of olefins,251 sulfides,252 and selenides253 (denoted as D) involves oxygen-atom transfer from nitrogen dioxide to yield epoxides, sulfoxides, and... 

Importantly, the oxidations in equation (90) are considerably accelerated in the presence of added salt such as n-Bu4N+PF and markedly retarded in nonpolar solvents (such as CCI4 and hexane) as well as in the presence of added nitrate salts, which suggests the critical role of ionic intermediates (viz. NO+NOf).251-253 Accordingly, the ionic mechanism for the oxygen-atom transfer from NO to various donors is outlined in Scheme 24. 

Note that under these conditions the thermal reaction in equation (90) is too slow to compete.) Finally, the stoichiometry for the oxygen-atom transfer from NO to the donor cation radical in equation (93) is independently established by the reaction of isolated cation radical intermediates with NO. 251,252... 

The epoxidation of electron-deficient alkenes, particularly a,P-unsaturated carbonyl compounds, continues to generate much activity in the literature, and this has been the subject of a recent concise review <00CC1215>. Additional current contributions in this area include a novel epoxidation of enones via direct oxygen atom transfer from hypervalent oxido-).3-iodanes (38), a process which proceeds in fair to good yields and with complete retention of... 

C. Oxygen Atom Transfer from Sulfoxide to Sulfide... 

A further test of whether MeReO(mtp)PAr3 (5) catalyzes other oxygen atom transfer reactions was made through studies of this reaction,... 

A new generation of oxorhenium compounds has now been prepared. They catalyze oxidation reactions of a different type, and appear to function by a different mechanism. They are oxorhenium(V) compounds that form usually metastable dioxorhenium(VII) intermediates. The mechanisms feature Rev(0)-to-ReVII(0)2 interconversions and catalyze oxygen atom transfer reactions. The mechanisms show a certain diversity as to the steps that enter in a kinetic sense. Yet the schemes presented in this review show a great deal of similarity in their overall mode of action. 

Mechanistically, the epoxidation appears to proceed via oxygen-atom transfer from the high-valent oxometallo intermediate (A) to organic substrates. 

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