An unprecedentedly reactive iron species (2) has been generated by reaction of excess peracetic acid with a mononuclear iron complex [FeII(CF3SO3)2(PyNMe3)] (1) at cryogenic temperatures, and characterized spectroscopically. 2 is kinetically competent for breaking strong C-H bonds of alkanes (BDE ~ 100 kcal·mol-1) through a hydrogen-atom transfer mechanism, and the transformations proceed with stereoretention and regioselectively, responding to bond strength, as well as to steric and polar effects. Bimolecular reaction rates are at least an order of magnitude faster than those of the most reactive synthetic high-valent nonheme oxoiron species described to date. EPR studies in tandem with kinetic analysis show that the 490-nm chromophore of 2 is associated with two S = ½ species in rapid equilibrium. The minor component 2a (5% iron) has g-values at 2.20, 2.19 and 1.99 characteristic of a low-spin iron(III) center and it is assigned as [FeIII(OOAc)(PyNMe3)]2+, also by comparison with the EPR parameters of the structurally characterized hydroxamate analogue [FeIII(tBuCON(H)O)(PyNMe3)]2+ (4). The major component 2b (40% iron, g-values = 2.07, 2.01, 1.95) has unusual EPR parameters and it is proposed to be [FeV(O)(OAc)(PyNMe3)]2+, where the O-O bond in 2a has been broken. Consistent with this assignment, 2b undergoes exchange of its acetate ligand with CD3CO2H and very rapidly reacts with olefins to produce the corresponding syn-1,2-hydroxoacetate product. Therefore, this work constitutes the first example where synthetic non-heme iron species responsible for stereospecific and site selective C-H hydroxylation are spectroscopically trapped, and its catalytic reactivity against C-H bonds can be directly interrogated by kinetic methods. Therefore, the accumulated evidence indicates that 2 consists mainly of an extraordinarily reactive [FeV(O)(OAc)(PyNMe3)]2+ (2b) species capable of hydroxylating unactivated alkyl C-H bonds with stereoretention in a rapid and site-selective manner, and that exists in fast equilibrium with its [FeIII(OOAc)(PyNMe3)]2+ precursor.
This research output has an Altmetric Attention Score of 10. This is our high-level measure of the quality and quantity of online attention that it has received. This Attention Score, as well as the ranking and number of research outputs shown below, was calculated when the research output was last mentioned on 22 September 2020.
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