Nucleophilic superoxide moiety

Fe(II), is assumed to be converted to a nucleophilic superoxide moiety and attack the ring at sites of low electron density. The carbon adjacent to the oxygen-bearing carbon is chosen as the position to be attacked by the oxygen species, but further discussion is necessary for the site of dioxygen attack on the aromatic ring. 

A mechanism for extradiol cleavage is proposed in Figure 18 [5,158], Substrate binds first to the iron(II) center, followed by 02, to form a ternary complex akin to the ES—NO complex described earlier. Electron transfer from metal to 02 in the Fe(II)—02 adduct results in a superoxide-like moiety and imparts nucleophilic character to the bound 02. This in turn generates semiquinone character on the bound substrate, which is attacked by the nascent superoxide to form a peroxy intermediate that decomposes by a Criegee-type rearrangement to the observed product. 

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