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

Abstract

An iron(II) complex, [(L1)FeII(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)FeIV(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 favours 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, displaying low yields of hydroxylated products, particularly with substrates containing strong C-H bonds. Self-quenching of 2 via 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 intermediates in an unconventional, highly electron-rich carbanionic ligand framework.