Generation of a High-Valent Iron Imido Corrolazine Complex and NR Group Transfer Reactivity

The generation of a new high-valent iron terminal imido complex prepared with a corrolazine macrocycle is reported. The reaction of [Fe^III(TBP₈Cz)] (TBP₈Cz = octakis­(4-tert-butylphenyl)­corrolazinato) with the commercially available chloramine-T (Na⁺TsNCl^–) leads to oxidative N-tosyl transfer to afford [Fe^IV(TBP₈Cz^+•)­(NTs)] in dichloromethane/acetonitrile at room temperature. This complex was characterized by UV–vis, Mössbauer (δ = −0.05 mm s^–1, ΔE_Q = 2.94 mm s^–1), and EPR (X-band (15 K), g = 2.10, 2.00) spectroscopies, and together with reactivity patterns and DFT calculations has been established as an iron­(IV) species antiferromagnetically coupled with a Cz-π-cation-radical (S_total = ¹/₂ ground state). Reactivity studies with triphenylphosphine as substrate show that [Fe^IV(TBP₈Cz^+•)­(NTs)] is an efficient NTs transfer agent, affording the phospharane product Ph₃PNTs under both stoichiometric and catalytic conditions. Kinetic analysis of this reaction supports a bimolecular NTs transfer mechanism with rate constant of 70(15) M^–1 s^–1. These data indicate that [Fe^IV(TBP₈Cz^+•)­(NTs)] reacts about 100 times faster than analogous Mn terminal arylimido corrole analogues. It was found that two products crystallize from the same reaction mixture of Fe^III(TBP₈Cz) + chloramine-T + PPh₃, [Fe^IV(TBP₈Cz)­(NPPh₃)] and [Fe^III(TBP₈Cz)­(OPPh₃)], which were definitively characterized by X-ray crystallography. The sequential production of Ph₃PNTs, Ph₃PNH, and Ph₃PO was observed by ³¹P NMR spectroscopy and led to a proposed mechanism that accounts for all of the observed products. The latter Fe^III complex was then rationally synthesized and structurally characterized from Fe^III(TBP₈Cz) and OPPh₃, providing an important benchmark compound for spectroscopic studies. A combination of Mössbauer and EPR spectroscopies led to the characterization of both intermediate spin (S = ³/₂) and low spin (S = ¹/₂) Fe^III corrolazines, as well as a formally Fe^IV corrolazine which may also be described by its valence tautomer Fe^III(Cz^+•).