Reactivity of coordinated dioxygen

Explanations that have been advanced to explain the enhanced reactivity of coordinated dioxygen include ... 

The reactivity of coordinated dioxygen is probably the area in which the historical divisions mentioned in the introduction have proved the most durable. The recent studies of the rf dioxygen complexes of iron have shown the very considerable changes produced by moving one element away from the well-known cobalt complexes. Dioxygen is exceptional in the extent to which its reactivity is changed by the metal to which it is coordinated, and there remains considerable scope for experimental investigation. 

Studies of the simple electron transfer properties of coordinated dioxygen are in a preliminary stage. The definition of reactivity patterns is obscured by inconsistencies and the lack of key pieces of information, as indicated by the comments above. Nevertheless, there is hope that some general features will emerge ... 

The present volume is a non-thematic issue and includes seven contributions. The first chapter byAndreja Bakac presents a detailed account of the activation of dioxygen by transition metal complexes and the important role of atom transfer and free radical chemistry in aqueous solution. The second contribution comes from Jose Olabe, an expert in the field of pentacyanoferrate complexes, in which he describes the redox reactivity of coordinated ligands in such complexes. The third chapter deals with the activation of carbon dioxide and carbonato complexes as models for carbonic anhydrase, and comes from Anadi Dash and collaborators. This is followed by a contribution from Sasha Ryabov on the transition metal chemistry of glucose oxidase, horseradish peroxidase and related enzymes. In chapter five Alexandra Masarwa and Dan Meyerstein present a detailed report on the properties of transition metal complexes containing metal-carbon bonds in aqueous solution. Ivana Ivanovic and Katarina Andjelkovic describe the importance of hepta-coordination in complexes of 3d transition metals in the subsequent contribution. The final chapter by Sally Brooker and co-workers is devoted to the application of lanthanide complexes as luminescent biolabels, an exciting new area of development. 

Such an intermediate can be formed because of the nucleophilic reactivity of a dioxygen molecule when complexed to iridium(I) and because of the known propensity of a coordinated carbonyl ligand to undergo such nucleophilic attack. 

Further studies revealed that electron-deficient alkenes are capable of displacing O2 from a peroxopalladium(II) complex. The reaction of nitrostyrene derivatives with (bc)Pd(02) results in quantitative displacement of dioxygen and formation of the (bc)Pd(ns ) complex (i.e., the reverse reaction in Eq. 21) [138]. Moreover, preliminary results reveal that dioxygen and BQ undergo reversible exchange at a bathocuproine-coordinated Pd center (Eq. 22) (Popp BV, Stahl SS, unpublished results). This observation is the most direct experimental result to date that establishes the similar reactivity of dioxygen and BQ with palladium. 

While most superoxo complexes—in contrast to peroxo compounds— have been assigned a bent, end-on coordination mode [9], the superoxide ligand of Tp Cr(02)Ph was suggested to exhibit the more unusual side-on (r] ) coordination [10]. The reactivity of the complex did not allow for the determination of its molecular structure however, close analogs could be isolated, crystallized and structurally characterized by X-ray diffraction. For example, the reaction of [Tp Cr(pz H)]BARF (pz H = 3-tert-butyl-5-methylpyrazole, BARF = tetrakis(3,5-bis(trifiuoromethyl)phenyl)borate) with O2 produced the stable dioxygen complex [Tp Cr(pz H)( ] -02)]BARF (Scheme 3, bottom), which featured a side-on bound superoxide ligand (do-o = 1.327(5) A, vo-o = 1072 cm ) [11]. Other structurally characterized... 

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