IronIV

Iron(IV) refers to iron in the +4 oxidation state. In coordination and inorganic chemistry, Fe(IV) species are less common and often transient compared with Fe(II) and Fe(III). The most studied Fe(IV) center is the ferryl group, Fe(IV)=O, found in various oxo-iron complexes. These ferryl species are highly reactive oxidants and frequently serve as key intermediates in oxidation reactions.

In biological systems, high-valent iron intermediates explain much of the reactivity of iron-dependent enzymes. In heme enzymes such as cytochrome P450, Compound I is formally Fe(IV)=O with a porphyrin radical cation and is a potent oxidant for C–H bond activation. In non-heme iron enzymes, Fe(IV)=O species generated during catalytic cycles drive substrate oxidation, including hydroxylation and desaturation reactions. Other iron(IV) species observed in synthetic systems include Fe(IV)=NR or various oxo, nitrido, and other high-valent oxo-ligand environments stabilized by strong ligands.

Preparation and stabilization of Fe(IV) complexes typically involve oxidation of Fe(III) precursors with oxidants such as peracids, iodosylbenzene, or molecular oxygen under controlled conditions. Ligand frameworks that stabilize the +4 state include porphyrins, corroles, and tetradentate or octadentate amine-based ligands, which help support the high oxidation state and modulate reactivity.

Applications of iron(IV) chemistry span catalytic oxidation and biomimetic oxidation catalysts. Research aims to balance reactivity and selectivity while managing safety concerns associated with highly reactive high-valent species. Iron(IV) thus plays a crucial role in understanding enzymatic mechanisms and in the development of high-valent iron catalysts.