oxoironIV

Oxoiron(IV) refers to an iron center in the +4 oxidation state bearing an oxo ligand, typically written as FeIV=O. It is a high-valent iron–oxo species that plays a central role in both biological oxidation reactions and synthetic oxidation chemistry.

Structure and properties

FeIV=O species can adopt various coordination geometries depending on surrounding ligands, often described as octahedral or square-pyramidal. The Fe=O unit is short and highly reactive. The electronic state is commonly S = 1 or S = 2, with the exact spin depending on ligand field and coordination environment. Spectroscopic methods such as Mössbauer spectroscopy, EPR (sometimes silent or weak, depending on spin), resonance Raman (notably the characteristic Fe=O stretch around the 800–900 cm−1 region) and UV–visible spectroscopy are used to identify and characterize oxoiron(IV) complexes. X-ray crystallography can provide precise Fe–O bond lengths and geometry.

Formation and occurrence

In biology, oxoiron(IV) intermediates arise in several enzymatic systems. In heme enzymes such as cytochrome P450, ferryl species appear during the catalytic cycle, with Compound II often identified as an FeIV=O species. In non-heme iron enzymes, FeIV=O intermediates form during oxygen activation by 2-oxoglutarate–dependent dioxygenases. In synthetic chemistry, oxoiron(IV) complexes are generated by oxidizing FeII precursors with oxidants such as iodosylbenzene, peracids, or hydrogen peroxide, often in the presence of supporting ligands that stabilize the high-valent state.

Reactivity

Oxoiron(IV) species are potent oxidants capable of hydrogen-atom abstraction and oxygen-atom transfer reactions, enabling substrates such as alkanes, alkenes, and sulfides to be oxidized. They serve as key models for understanding high-valent iron chemistry and are studied for applications in selective oxidation catalysis and mechanistic enzymology.