Coordinated dioxygen, reactivity

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

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 ... 

Iridium complexes appear to be less reactive towards carbonyl compounds, although they react with aldehydes " and hexafluoroacetone . This last reaction has been studied kinetically, and the authors find it to be first order in dioxygen complex and in hexafluoroacetone. They conclude the reaction takes place by a direct electrophilic attack on the coordinated dioxygen. This contrasts sharply with the results of Ugo et al. for (Ph3P)2Pt02 the slow substitution reactions of Ir(III) complexes and the absence of vacant coordination sites exclude the coordination of the substrate prior to the attack on coordinated dioxygen, and this may account for the much slower reactions of the iridium complexes. 

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. 

In the past two decades, our understanding of the fundamentals of copper-dioxygen reactivity has flourished through coordination chemistry efforts... 

The reactivity of these t/ -oxygen compounds can be rationalized on the basis of the coordinated dioxygen having nucleophilic character. Thus, the compound Pt(PPh3)202 reacts with electrophiles such as S02, C02, and RCHO to give cyclic or acyclic... 

It should be added that MS-02 is not necessarily a mono-nuclear complex. It could be shown in a few cases that the catalytic activity of the metal ion is due to the formation of dinuclear metal-substrate complexes. Presumably in these species each oxygen atom of dioxygen coordinates to a different metal center. Such systems were extensively used to model the reactivity patterns of various enzymes containing a bimetallic active center. 

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