Adduct formation, dioxygen

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

The question arises as to the actual sequence of events that end up in the reduction of dioxygen into water. Even though complementary investigation is needed before a complete answer could be proposed, several observations are worth mentioning provisionally. The reoxidation of reduced heteropolyanions by dioxygen after the catalytic processes in which they participate is a popular practice. Its mechanism was generally and indistinctly explained to go through an intermediate adduct formation accompanied by inner sphere electron transfers [164]. 

There are three different approaches which can be employed to prevent irreversible oxidation of iron(II) porphyrins and promote dioxygen adduct formation (1) low temperatures to reduce the rate of dimerization (2) steric hindrance to prevent dimerization and (3) immobilization of the heme to prevent dimerization. 

Some recent systems have concentrated more on using complexes that are known to form 02-adducts however, in nearly all cases, 1 1 dioxygen-adduct formation does not result under the conditions used for the attempted catalysis. For example, the following chemistry is well established for foi (salicylaldehyde)ethylenediimine Co(II), Co(salen), and other related Schiff-base and porphyrin-ligand systems (3, 6, 9, 113), Reactions 33 and 34. Dioxygen binding is exothermic,... 

The novel aspect of this mechanism to be demonstrated is the mode of substrate activation. Synthetic complexes have been useful in corroborating aspects of the proposed mechanism. Bianchini et al. demonstrated reversible dioxygen adduct formation for [(tri-phos)M "(catecholate)] [triphos = l,l,l-tris(diphenylphosphinomethyl)ethane M = Rh, Ir] complexes ". A crystal structure of the Ir adduct reveals the formation of an alkylperoxy moiety, similar to that proposed in the mechanism, coordinated in a tridentate manner to the metal center. However, oxidative ring cleavage of the complexes does not occur. 

Kryatov, S. V. Taktak, S. Korendovych, I. V. Rybak-Akimova, E. V. Kaizer, J. Stephane Torelli, S. Shan, X. Mandal, S. MacMurdo, V. Mairata i Payeras, A. Que, L., Jr. Dioxygen binding to complexes with Fen2( r-OH)2 cores steric control of activation barriers and 02-adduct formation. Inorg. Chem. 2005, 44 (1), 85-99. 

The kinetics of Cuz (Oz) adduct formation was also followed utilizing Tolman s [Cu ( -Pr3TACN)]+ (6 ) systems. Oxygenation of in acetone affords a Cuz-dioxygen... 

Heme-copper/dioxygen adduct formation, properties, and reactivity 07ACR563. 

At least one phosphate group is considered bound to the molbydenum(v). H2O2 reacts about 20 times faster than O2 with [Mo 2(cys)2] and addition of peroxide to Mo i yields the same product as that of the dioxygen reaction. If the metal complex is present in excess, however, there is evidence for adduct formation ... 

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