Octahedral iron(IV)–tosylimido complexesexhibiting single electron-oxidation reactivity

International audienceHigh 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))& xe001;NTs) and [Fe-IV(NTs)(Me-2(CHPy2)tacn)](OTf)(2) (2((IV))& xe001;NTs), (MePy(2)tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane, and Me-2(CHPy2)tacn = 1-(di(2-pyridyl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane, Ts = Tosyl). 1((IV))& xe001;NTs and 2((IV))& xe001;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(CHPy2)tacn, respectively). 1((IV))& xe001;NTs and 2((IV))& xe001;NTs are metastable and have been spectroscopically characterized by HR-MS, UV-vis, H-1-NMR, resonance Raman, Mossbauer, 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(CHPy2)tacn) have been isolated after the decay of 1((IV))& xe001;NTs and 2((IV))& xe001;NTs in solution, spectroscopically characterized, and the molecular structure of [Fe-III(HNTs)(MePy(2)tacn)](SbF6)(2) determined by single crystal X-ray diffraction. Reaction of 1((IV))& xe001;NTs and 2((IV))& xe001;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))& xe001;NTs and 2((IV))& xe001;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))& xe001;NTs and 2((IV))& xe001;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