An iron(IV)-oxo intermediate on a carbanionic ligand framework: reactivity and decay pathways

An iron(II) complex, [(L¹)Fe^II(CH₃CN)₂]⁺ (1), (L¹ = tris(2-pyridylthio)methanido) of the monoanionic N3C donor ligand, upon treatment with isopropyl 2-iodosylbenzoate, generates the iron(IV)-oxo intermediate, [(L¹)Fe^IV(O)(CH₃CN)]⁺ (2). The strong ligand field of the carbanionic ligand supports the S = 1 iron(IV)-oxo species, as evidenced from spectroscopic data. The DFT-calculated absorption spectrum and Mössbauer parameters favour the geometry where the oxo unit is disposed cis to the carbanionic donor. This short-lived species, with a half-life of 11 min at 278 K, performs HAT and OAT reactions. Although the intermediate is efficient in OAT reactions, it is less reactive in HAT reactions, affording low yields of hydroxylated products, particularly with substrates containing strong C-H bonds. Self-quenching of 2via the formation of an oxo-bridged dinuclear iron(III) species outperforms productive substrate oxidation. Intermediate 2 represents the unique example of an organoimetallic iron(IV)-oxo intermediate in an unconventional, highly electron-rich carbanionic ligand framework.