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 [FeIV(NTs)(MePy2tacn)](OTf)2 (1(IV) NTs) and [FeIV(NTs)(Me2(CHPy2)tacn)](OTf)2 (2(IV) NTs), (MePy2tacn = N-methyl-N,N-bis(2-picolyl)-1,4,7-triazacyclononane, and Me2(CHPy2)tacn = 1-(di(2-pyridyl)methyl)-4,7-dimethyl-1,4,7-triazacyclononane, Ts = Tosyl). 1(IV) NTs and 2(IV) NTs are rare examples of octahedral iron(IV)–imido complexes and are isoelectronic analogues of the recently described iron(IV)–oxo complexes [FeIV(O)(L)]2+ (L = MePy2tacn and Me2(CHPy2)tacn, respectively). 1(IV) NTs and 2(IV) NTs are metastable and have been spectroscopically characterized by HR-MS, UV-vis, 1H-NMR, resonance Raman, Mössbauer, and X-ray absorption (XAS) spectroscopy as well as by DFT computational methods. Ferric complexes [FeIII(HNTs)(L)]2+1(III)–NHTs (L = MePy2tacn) and 2(III)–NHTs (L = Me2(CHPy2)tacn) have been isolated after the decay of 1(IV) NTs and 2(IV)NTs in solution, spectroscopically characterized, and the molecular structure of [FeIII(HNTs)(MePy2tacn)](SbF6)2 determined by single crystal X-ray diffraction. Reaction of 1(IV) NTs and 2(IV) 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) NTs and 2(IV) 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) NTs and 2(IV) 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. It was published recently in Royal Society of Chemistry’s flagship journal Chemical Science.

G. Sabenya, I. Gamba, L. Gómez, M. Clémancey, J.R. Frisch, E.J. Klinker, G. Blondin, S. Torelli, L. Que, V. Martin-Diaconescu, J. Latour, J. Lloret-Fillol, and M. Costas
“Octahedral iron(iv )–tosylimido complexes exhibiting single electron-oxidation reactivity”
Chem. Sci. 2019, ASAP [abstract]
DOI: 10.1039/C9SC02526J