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 [Fe2 (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 [Fe3.5 (μ-O) 2 Fe3.5]3+ diamond core (1) into a complex with a valence-localized [HO-FeIII -O-FeIV =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) FeIV =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.
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