Dioxygen reactions involving

In strongly basic solution this reaction involves the formation of an hydroxo bridge in addition to the dioxygen bridge 43). The redox potential for the process... 

Martin effected the synthesis of several 3,5-diarylated indoles by a tandem Stille-Suzuki sequence [131]. The latter reaction involves exposure of 3-(3-pyridyl)-5-bromo-l-(4-toluenesulfonyl)indole with arylboronic acids (aryl = 3-thienyl, 2-furyl, phenyl) under typical conditions to give the expected products in 86-98% yield [131], Carrera engaged 6- and 7-bromoindole in Pd-catalyzed couplings with 4-fluoro- and 4-methoxyphenylboronic acids to prepare 6- and 7-(4-fluorophenyl)indole (90% and 74% yield) and 6-(4-methoxyphenyl)indole (73% yield) [29]. Banwell and co-workers employed 7-bromoindole in a Suzuki coupling with 3,4-dioxygenated phenylboronic acids en route to the synthesis of Amaryllidaceae alkaloids [132], Yields of 7-arylated indoles are 93-99%. Moody successfully coupled 4-bromoindole... 

Copper, like iron, is frequently encountered in reactions involving dioxygen. The copper enzyme laccase catalyses the oxidation of uroshiol (the same poisonous substance found in poison oak and ivy) in the production of Japanese lacquer. It is the products of uroshiol oxidation, which are responsible for the lacquer s remarkable material properties. 

Most known reactions of dioxygen species involve inner-sphere pathways, or adduct formation. Our studies of the... 

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... 

Main reactions involving the catalytic reduction of dioxygen fall into one of two categories. Molecular oxygen undergoes either a two-electron reduction (generally in the presence of individual catalyst molecules). 

A different type of concerted reaction involves the bacterial cytochrome c peroxide, where two hemes are coupled together, so that hydrogen peroxide undergoes a two-electron reduction to water without the formation of radical species. In a number of dioxygenases, dioxygen is reduced to peroxide by concerted electron transfer from [2Fe-2S] and non-heme Fe11 centres. 

Standard potentials for redox reactions involving oxygen at 25°C. (From Sawyer, D.T. and Nanni, E.J., Jr., Redox chemistry of dioxygen species and their chemical reactivity, in Oxygen and Oxy-Radicals in Chemistry and Biology, Rodgers, M.A.J. and Powers, E.L., Eds., Academic Press, New York, 1981,15 44. With permission.)... 

Another common type of reaction involving sulfur compounds is the oxidation of thiols or thiolates to disulfides. This process is found to be very sensitive to the presence of metal ions. The metal can act as the primary oxidant, or dioxygen may be involved in a reaction with a co-ordinated thiol (Fig. 9-10). Very often, oxidation reactions involving metal ions and thiols are catalytic in the metal. 

Figure 9-32. The oxidation of the complex [Fe(9.18)]3 with dioxygen gives complexes of the new ligand 9.19. The first step of the reaction involves the formation of superoxide, which is responsible for the breaking of the first C-H bond in the second step of the reaction. The overall mechanism is characterised by the interconversion of radical and anionic species by a series of one-electron transfers.

More recent investigations have shown that these reactions involve metal-catalyzed decomposition of hydroperoxides via the usual redox cycles. Thus, inhibition, polymerization and product studies in the RhCl(Ph3 P)3-catalyzed autoxidation of cyclohexene,136 ethylbenzene,136 and diphenylmethane137 were compatible only with metal-catalyzed decomposition of the alkyl hydroperoxide and not a direct reaction of the metal-dioxygen complex with substrate. Complexes Rh(III) (acac)3, Rh(III) (2-ethylhexanoate)3, and Co(II) (2-ethylhexanoate)2, gave results that were almost the same as those obtained with RhCl(Ph3P)3. The redox cycle may involve Rh(II) and Rh(III) ... 

The aerobic oxidation of alcohols is catalysed by both low- and high-valent forms of the metal. In the former case the reaction involves (Fig. 5) the formation of a hydridometal species (or its equivalent), while the latter involves an oxometal intermediate (Fig. 6) which is regenerated by reaction of the reduced form of the catalyst with dioxygen instead of a peroxide. It is difficult to distinguish between the two and one should bear in mind, therefore, that aerobic oxidations with high-valent oxometal catalysts could involve the formation of low-valent species, even the (colloidal) metal, as the actual catalyst. 

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