Million-fold activation of the [Fe2(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 centres-such as that of methane monooxygenase in methane hydroxylation-through dioxygen activation mechanisms. High valent species with [Fe-2(mu-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(mu-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 a 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 centre to a high-spin (S = 2) centre, and the concentration of the oxidizing capability to the active terminal oxoiron(IV) moiety. This suggests that similar isomerization strategies might be used by nonhaem diiron enzymes.