Mechanisms olefination, oxygen oxidant

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... 

Catalytic oxidative transformations of lower alkanes attract the attention as possible ways to transfer these substances into more suitable chemicals - olefins and oxygenates (alcohols, aldehydes, acids, etc.) - and to involve them into the industrial use as raw materials for chemical and petrochemical synthesis. However, the yields of desirable products reached up to date are not sufficiently high. The progress in the studies of intrinsic mechanism of catalytic partial oxidation of lower alkanes is not sustainable either. We believe that these two facts are correlated and that the analysis we performed in the present work can brighten up some important details of the mechanism of catalytic oxidation of lower alkanes. ... 

The reaction mechanism for the oxidation of olefins by metal ions / complexes in homogeneous medium is studied widely and the formation of peroxo and oxo complexes was suggested to be responsible for the transfer of oxygen to the substrate. Vaska et al., have reported formation of peroxo complexes when dioxygen is bound covalently to the metal centre [16]. The formation of 0X0 complex and the transfer of oxygen via this route has been suggested by Taqui Khan et al., in the oxidation of olefins catalysed by Ru(III) complex in homogeneous medium [17]. On the basis... 

Preliminary results of the reaction between vanadium(iii)-tetrasulpho-phthalocyanine complex with oxygen have been reported these data were compared with those obtained for the corresponding reaction of the hexa-aquo complex ion. The oxidation of methyl ethyl ketone by oxygen in the presence of Mn"-phenanthroline complexes has been studied Mn " complexes were detected as intermediates in the reaction and the enolic form of the ketone hydroperoxide decomposed in a free-radical mechanism. In the oxidation of 1,3,5-trimethylcyclohexane, transition-metal [Cu", Co", Ni", and Fe"] laurates act as catalysts and whereas in the absence of these complexes there is pronounced hydroperoxide formation, this falls to a low stationary concentration in the presence of these species, the assumption being made that a metal-hydroperoxide complex is the initiator in the radical reaction. In the case of nickel, the presence of such hydroperoxides is considered to stabilise the Ni"02 complex. Ruthenium(i) chloride complexes in dimethylacetamide are active hydrogenation catalysts for olefinic substrates but in the presence of oxygen, the metal ion is oxidised to ruthenium(m), the reaction proceeding stoicheiometrically. Rhodium(i) carbonyl halides have also been shown to catalyse the oxidation of carbon monoxide to carbon dioxide under acidic conditions ... 

Studies on the mechanism of other olefin oxygenations, such as allylic oxidation, glycol formation and redox hydration can be expected in the near future. 

A detailed account of the mechanisms of catalytic oxidation processes has been published. The mechanisms of the catalytic oxidation of terminal oleffns to methyl ketones and of the catalytic epoxidation of olefins with hydroperoxides have also been reviewed. The latter reactions are generally thought to proceed via direct attack of the substrate upon an electrophilic oxygen of a metal peroxo species rather than prior complexa-... 

The oxidation of ethylene exclusively to acetaldehyde (and other straight-chained olefins to ketones) is achieved by the catalytic reaction of ethylene in an aqueous solution by palladium(II) chloride or by oxygen in the presence of palladium(II) chloride, copper(II) chloride, or iron(III) chloride. Generally, the oxidation of olefins by other metal ions, such as Hg(II), Th(III), and Pb(IV) yields glycol derivatives as well as carbonyl products. The mechanism for the oxidation is plausibly accommodated in the scheme shown in Fig. 7-12. 

Selective oxidation and ammoxldatlon of propylene over bismuth molybdate catalysts occur by a redox mechanism whereby lattice oxygen (or Isoelectronlc NH) Is Inserted Into an allyllc Intermediate, formed via or-H abstraction from the olefin. The resulting anion vacancies are eventually filled by lattice oxygen which originates from gaseous oxygen dlssoclatlvely chemisorbed at surface sites which are spatially and structurally distinct from the sites of olefin oxidation. Mechanistic details about the... 

During the last three decades, peroxo compounds of early transition metals (TMs) in their highest oxidation state, like TiIV, Vv, MoVI, WV1, and Revn, attracted much interest due to their activity in oxygen transfer processes which are important for many chemical and biological applications. Olefin epoxidation is of particular significance since epoxides are key starting compounds for a large variety of chemicals and polymers [1]. Yet, details of the mechanism of olefin epoxidation by TM peroxides are still under discussion. 

The anodic oxidation of 1,3-diketones in the presence of olefins in an oxygen atmosphere gave the extremely stable cyclic peroxides 80 in good yield [101,102] (Scheme 40). A catalytic amount of electricity was sufiicient for the reaction and an electro-intiated radical chain mechanism was suggested. 

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