Oxygen dioxygen, oxidation with

There are many reviews that cover various aspects of oxidation. These include ones on alkane activation,166 catalytic selective oxidation,167 metal complexes of dioxygen,168 metal-catalyzed oxidation,169 biomimetic oxidations,170 oxidation with peroxides,171 catalytic oxidations with peroxides,172 catalytic oxidations with oxygen,173 oxidations with dioxiranes,174 and oxidation of pollutants.175... 

Dioxygen is a cheap and ideal source of oxygen but it is very difficult to activate and there are relatively few examples of 02 oxidations catalyzed by zeolite-encapsulated complexes. Encapsulated CoPc is active for the oxidation of propene to aldehyde, whereas the free complex is inactive.104 A triple catalytic system, Pd(OAc)2, benzoquinone, and a metal macrocycle, was used to oxidize alkenes with molecular oxygen at room temperature.105 Zeolite-encapsulated FePc106-108 and CoSalophen (Scheme 7.5)107109 complexes were used as oxygen-activating catalysts. With the use of a Ru complex instead of Pd(OAc)2 in the triple catalytic system, primary alcohols can be oxidized selectively to aldehydes.110... 

Salts of transition metals are widely used in technological processes for the preparation of various oxygen-containing compounds from hydrocarbon raw materials. The principal mechanism of acceleration of RH oxidation by dioxygen in the presence of salts of heavy metals was discovered by Bawn [46 19] for benzaldehyde oxidation (see Chapter 1). Benzaldehyde was oxidized with dioxygen in a solution of acetic acid, with cobalt acetate as the catalyst. The oxidation rate was found to be [50] ... 

The vast majority of the studies in this field relate to the oxidation of iron ions by molecular oxygen. The oxidation of Fe2+ is first-order with respect to dioxygen and,... 

The use of six equivalents of dihydrogen peroxide leads to a clean conversion of the dithiolate complex to the disulfonate compound. Earlier studies on oxidation of nickel thiolates showed that oxidations with dioxygen stop at monosulfinates. Our observation and the characterization of the first chelating bis-sulfonato nickel complex formed from the direct oxidation of a mononuclear nickel dithiolate, may also provide new insight into the chemistry of sulfur-rich nickel-containing enzymes in the presence of oxygen. 

The olefin oxygenations carried out with dioxygen seem to be metal-centered processes, which thus require the coordination of both substrates to the metal. Consequently, complexes containing the framework M (peroxo)(olefin) represent key intermediates able to promote the desired C-0 bond formation, which is supposed to give 3-metalla -l,2-dioxolane compounds (Scheme 6) from a 1,3-dipolar cycloinsertion. This situation is quite different from that observed in similar reactions involving middle transition metals for which the direct interaction of the olefin and the oxygen coordinated to the metal, which is the concerted oxygen transfer mechanism proposed by Sharpless, seems to be a more reasonable pathway [64] without the need for prior olefin coordination. In principle, there are two ways to produce the M (peroxo)(olefin) species, shown in Scheme 6, both based on the easy switch between the M and M oxidation states for... 

Dioxygen oxidizes VC13 or VCl(salen) to vanadium(IV) with the intermediate formation of dioxygen adducts,235 with equilibrium constants of the order of 102 they are involved in the catalysis of oxygenation of 3,5-di-r-butylpyrocatechol.236... 

The general profile of the dioxygen oxidation of tetraaryldisilenes is shown in Eq. (63).7 Both in the solid state and in solution, the initial oxidation product of a tetraaryldisilene is the corresponding 1,2-disiladioxetane 145, whose intramolecular isomerization gives the thermodynamically more stable 1,3-disiladioxetane 146. All the steps of the oxidation occur intramolecularly and with the retention of stereochemistry around the Si-Si bond. While a small amount of disilaoxirane 147 is produced in the oxidation in low-temperature solution, 147 is converted to 146 smoothly in the presence of excess oxygen. 

The existence of numerous oxygenases that catalyze the direct oxygenation of organic substrates continues to stimulate the search for atom transfer oxidations of hydrocarbons by simple metal-dioxygen complexes. (For a further discussion of reactions of metal-dioxygen complexes with organic substrates via heterolytic pathways, see Section III.C). 

Ruthenium-catalysed oxidations with dioxygen or hypochlorite are currently methods of choice for the oxidation of alcohol, ethers, amines and amides. In hydrocarbon oxidations, in contrast, ruthenium has not yet lived up to expectations. The proof of principle with regard to direct oxidation of, for example, olefins, with dioxygen via a nonradical, Mars-van Krevelen pathway has been demonstrated but this has, as yet, not led to practically viable systems with broad scope. The problem is one of rate although feasible the heterolytic oxygen-transfer pathway cannot compete effectively with the ubiquitous free-radical autoxidation. 

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