Electronic Structure and Reactivity of Dioxygen-Derived AliphaticThiolate-Ligated Fe-Peroxo and Fe(IV) Oxo Compounds

Herein, we examine the electronic and geometricstructural properties of O2-derived aliphatic thiolate-ligated Fe-peroxo, Fe-hydroxo, and Fe(IV) oxo compounds. The latter cleavesstrong C-H bonds (96 kcal mol-1) on par with the valine C-Hbond cleaved by isopencillin N synthase (IPNS). Stopped-flowkinetics studies indicate that the barrier to O2binding to[FeII(SMe2N4(tren))]+(3) is extremely low (Ea= 36(2) kJmol-1), as theoretically predicted for IPNS. Dioxygen binding to3is shown to be reversible, and a superoxo intermediate,[FeIII(SMe2N4(tren))(O2)]+(6), forms in thefirst 25 ms of thereaction at-40 degrees C prior to the rate-determining (Ea= 46(2) kJmol-1) formation of peroxo-bridged [(SMe2N4(tren))Fe(III)]2(mu-O2)2+(7). A log(kobs) vs log([Fe]) plot for the formation of7is consistent with the second-order dependence on iron, and H2O2assays are consistent with a 2:1 ratio of Fe/H2O2. Peroxo7is shown to convert to ferric-hydroxo [FeIII(SMe2N(tren))(OH)]+(9,g perpendicular to= 2.24,g???= 1.96), the identity of which was determined via its independent synthesis. Rates of the conversion7 -> 9are shown to bedependent on the X-H bond strength of the H-atom donor, with akH/kD= 4 when CD3OD is used in place of CH3OH as a solvent.A crystallographically characterizedcisthiolate-ligated high-valent iron oxo, [FeIV(O)(SMe2N4(tren))]+(11), is shown to form enroute to hydroxo9. Electronic structure calculations were shown to be consistent with11being anS= 1 Fe(IV)???O with anunusually high nu Fe-Ostretching frequency at 918 cm-1in line with the extremely short Fe-O bond (1.603(7) A)

Automated summary

In this study, the electronic and geometric structural properties of O2-derived aliphatic thiolate-ligated Fe-peroxo, Fe-hydroxo, and Fe(IV) oxo compounds were examined. The results showed that the Fe(IV) oxo compounds are capable of cleaving strong C-H bonds and forming peroxo intermediates. Additionally, the formation processes of several reaction intermediates were discovered through experimental and computational studies.