Octahedral iron(iv)–tosylimido complexes exhibiting single electron-oxidation reactivity

High valent iron species are very reactive molecules involved in oxidation reactions of relevance to biology and chemical synthesis. Herein we describe iron(iv)–tosylimido complexes [Fe(IV)(NTs)(MePy(2)tacn)](OTf)(2) (1((IV))[double bond, length as m-dash]NTs) and [Fe(IV)(NTs)(Me(2)(CHPy(2))tacn)](OTf)(2) (2((IV))[double bond, length as m-dash]NTs), (MePy(2)tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane, and Me(2)(CHPy(2))tacn = 1-(di(2-pyridyl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane, Ts = Tosyl). 1((IV))[double bond, length as m-dash]NTs and 2((IV))[double bond, length as m-dash]NTs are rare examples of octahedral iron(iv)–imido complexes and are isoelectronic analogues of the recently described iron(iv)–oxo complexes [Fe(IV)(O)(L)](2+) (L = MePy(2)tacn and Me(2)(CHPy(2))tacn, respectively). 1((IV))[double bond, length as m-dash]NTs and 2((IV))[double bond, length as m-dash]NTs are metastable and have been spectroscopically characterized by HR-MS, UV-vis, (1)H-NMR, resonance Raman, Mössbauer, and X-ray absorption (XAS) spectroscopy as well as by DFT computational methods. Ferric complexes [Fe(III)(HNTs)(L)](2+), 1((III))–NHTs (L = MePy(2)tacn) and 2((III))–NHTs (L = Me(2)(CHPy(2))tacn) have been isolated after the decay of 1((IV))[double bond, length as m-dash]NTs and 2((IV))[double bond, length as m-dash]NTs in solution, spectroscopically characterized, and the molecular structure of [Fe(III)(HNTs)(MePy(2)tacn)](SbF(6))(2) determined by single crystal X-ray diffraction. Reaction of 1((IV))[double bond, length as m-dash]NTs and 2((IV))[double bond, length as m-dash]NTs with different p-substituted thioanisoles results in the transfer of the tosylimido moiety to the sulphur atom producing sulfilimine products. In these reactions, 1((IV))[double bond, length as m-dash]NTs and 2((IV))[double bond, length as m-dash]NTs behave as single electron oxidants and Hammett analyses of reaction rates evidence that tosylimido transfer is more sensitive than oxo transfer to charge effects. In addition, reaction of 1((IV))[double bond, length as m-dash]NTs and 2((IV))[double bond, length as m-dash]NTs with hydrocarbons containing weak C–H bonds results in the formation of 1((III))–NHTs and 2((III))–NHTs respectively, along with the oxidized substrate. Kinetic analyses indicate that reactions proceed via a mechanistically unusual HAT reaction, where an association complex precedes hydrogen abstraction.