A Mononuclear Nonheme Iron(V)-Imido Complex

Abstract

Mononuclear nonheme iron(V)-oxo complexes have been reported previously. Herein, we report the first example of a mononuclear nonheme iron(V)-imido complex bearing a tetraamido macrocyclic ligand (TAML), [(TAML)FeV(NTs)]− (1). The spectroscopic characterization of 1 revealed an S = 1/2 Fe(V) oxidation state, an Fe—N bond length of 1.65(4) Å, and an Fe—N vibration at 817 cm−1. The reactivity of 1 was demonstrated in C—H bond functionalization and nitrene transfer reactions.

Uncatalyzed Oxidative C−H Amination of 9,10‐Dihydro‐9‐Heteroanthracenes: A Mechanistic Study

“…Therefore, dihydroheteroanthracenes are often assumed to be suitable model substrates to test for basic C−H amination activity, even for relatively non‐reactive nitrene intermediates . Especially xanthene is a commonly used substrate to investigate reaction kinetics of such reactions …”

“…[25,26] Our group is interested in the formation and characterization of new metal-nitrene complexes from known nitrenep recursors and ideally directly from primarya mines.A so thers, we adopted the reasoning that successful nitrene transfer could be dictated by the relative bond dissociation free energy (BDFE) of the CÀHb ond, with al ower BDFE expectedly resulting in faster nitrene insertion. [25,[27][28][29][30][31][32][33] Dihydroheteroanthracenes (xanthene,t hioxanthene, and dihydroacridine derivatives) have low CÀHb ond dissociation energies (BDE) in the range of 74-81 kcal mol À1 . [34] Therefore, dihydroheteroanthracenes are often assumedt ob es uitable model substrates to test forb asic CÀH amination activity,even for relativelynon-reactive nitrene intermediates.…”

Achieving One-Electron Oxidation of a Mononuclear Nonheme Iron(V)-Imido Complex

“…Moreover, unlike the iron(IV and V)-oxo systems, most of the synthetic iron-imido complexes reported so far are limited to iron(IV)-imido complexes, 5 and a mononuclear iron(V)-imido complex bearing a highly negatively charged TAML, [Fe V (NTs)(TAML)] − ( 1 ), was successfully synthesized by some of us very recently. 6 Encouraged by the successful synthesis of 1 , we attempted to oxidize it further to obtain a species such as [Fe VI (NTs)-(TAML)]. Interestingly, we observed that the iron(V)-imido complex was oxidized at the TAML site, but not at the iron center.…”

“…Titration experiments, monitored at 750 nm as a function of the amount of [Ru(bpy) 3 ] 3+ added (Figure 1a, inset), indicated that the complete conversion of 1 to 2 required a stoichiometric amount of the [Ru(bpy) 3 ] 3+ oxidant. While the X-band EPR spectrum of 1 exhibited an isotropic signal at g = 2.00, 6 2 is EPR silent (SI, Figure S3). The latter result suggests that (i) a low-spin ( S = 1/2) iron(V) in 1 was oxidized to iron(VI) ( S = 0) or (ii) a one-electron oxidized TAML was antiferromagnetically or ferromagnetically coupled with ( S = 1/2) iron(V) (vide infra).…”

“…By comparing the k 2 values of 1 and 2 , we found that the reactivity of the iron(V)-imido complex was markedly enhanced (over 10 4 folds) by the one-electron oxidation of the supporting ligand (e.g., 2.6 × 10 −2 M −1 s −1 for 1 versus 4.4 × 10 2 M −1 s −1 for 2 ). 6 The analysis of the reaction solution revealed the formation of PhS(=NTs)CH 3 (~95% yield) and [Fe IV (TAML)] as products (SI, Figures S22 and S23). In addition, as often proposed in the sulfoxidation of thioanisoles by high-valent metal-oxo species, 12 a large negative slope of −9.1, which was obtained by plotting log k 2 values against one-electron oxidation potentials ( E ox ) of para -X-substituted thioanisoles (Figure 3b; SI, Figure S24 and Table S6), suggests that the sulfimidation of thioanisoles by 2 proceeds via electron transfer, followed by nitrene transfer.…”