Adduct formation, dioxygen species

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

The first step consists of the formation of the dioxygen adduct which can have either a superoxo structure (1) if the metal is a potential one-electron donor, or a peroxo structure (2) if the metal is a potential two-electron donor. These superoxo or peroxo complexes can be considered as the formal, but not chemical, analogs of the superoxide 02 and peroxide 022- anions. The superoxo complex (1) can further react with a second reduced metal atom to give the /x-peroxo species (3), which can cleave itself into the oxo species (4), which may be hydrolyzed to give the hydroxo species (6) or react with a second metal atom to give the p.-oxo species (5). The alkylperoxo (7) and hydroperoxo (8) species can result from the alkylation or protonation of the peroxo species (2), or from anion exchange from metal salts by alkyl hydroperoxides or hydrogen peroxide. 

Rh2(DPB). In contrast to the dimers [Rh(P)]2, this compound reacted with dihydrogen only after intermediate addition of CO to yield a hydride (RhH)2(DPB) with two Rh-H bonds probably located inside the cavity, An insertion of CO into the Rh-H bonds, as with RhH(P) (see Sect. 4.2), was not observed. The dihydride was able to be dehydrogenated with molecular oxygen to reform Rh2(DPB) the formation of a dioxygen adduct (p-peroxo derivative) of the dirhodium(II) species which might be expected according to Scheme 3 (paths — q, t, u) was not observed. 

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