Direct observation of a nonheme iron(IV)-oxo complex that mediates aromatic C-F hydroxylation

The synthesis of a pentadentate ligand with strategically designed fluorinated arene groups in the second coordination sphere of a nonheme iron center is reported. The oxidatively resistant fluorine substituents allow for the trapping and characterization of an Fe(IV)(O) complex at -20 °C. Upon warming of the Fe(IV)(O) complex, an unprecedented arene C-F hydroxylation reaction occurs. Computational studies support the finding that substrate orientation is a critical factor in the observed reactivity. This work not only gives rare direct evidence for the participation of an Fe(IV)(O) species in arene hydroxylation but also provides the first example of a high-valent iron-oxo complex that mediates aromatic C-F hydroxylation.