Million-fold activation of the [Fe(2)(μ-O)(2)] diamond core for C-H bond cleavage

In biological systems, the cleavage of strong C–H bonds is often carried out by iron centers – such as the methane monooxygenase in methane hydroxylation – through dioxygen activation mechanisms. High valent species with [Fe(2)(μ-O)(2)] diamond cores are thought to act as the oxidizing moieties, but the synthesis of complexes that cleave strong C–H bonds efficiently has remained a challenge. We report here the conversion of a synthetic complex with a valence-delocalized [Fe(3.5)(μ-O)(2)Fe(3.5)](3+) diamond core (1) into a complex with a valence-localized [HO-Fe(III)-O-Fe(IV)=O](2+) open core (4), which cleaves C–H bonds over million-fold faster. This activity enhancement results from three factors: the formation of a terminal oxoiron(IV) moiety, the conversion of the low-spin (S = 1) Fe(IV)=O center to a high-spin (S = 2) center, and the concentration of the oxidizing capability to the active terminal oxoiron(IV) moiety. This suggests that similar isomerization strategies might be employed by nonheme diiron enzymes.