| Popis: |
Herein, we examine the electronic and geometric structural properties of O(2)-derived aliphatic thiolate-ligated Feperoxo, Fe-hydroxo, and Fe(IV) oxo compounds. The latter cleaves strong C–H bonds (96 kcal mol(−1)) on par with the valine C–H bond cleaved by isopencillin N synthase (IPNS). Stopped-flow kinetics studies indicate that the barrier to O(2) binding to [Fe(II)(S(Me2)N(4) (tren))](+) (3) is extremely low (E(a) = 36(2) kJ mol(−1)), as theoretically predicted for IPNS. Dioxygen binding to 3 is shown to be reversible, and a superoxo intermediate, [Fe(III)(S(Me2)N(4)(tren))(O(2))](+) (6), forms in the first 25 ms of the reaction at −40 °C prior to the rate-determining (E(a) = 46(2) kJ mol(−1)) formation of peroxo-bridged [(S(Me2)N(4)(tren))Fe(III)](2)(μ-O(2))(2+) (7). A log(k(obs)) vs log([Fe]) plot for the formation of 7 is consistent with the second-order dependence on iron, and H(2)O(2) assays are consistent with a 2:1 ratio of Fe/H(2)O(2). Peroxo 7 is shown to convert to ferric-hydroxo [Fe(III)(S(Me2)N(tren))(OH)](+) (9, g(⊥) = 2.24, g(∥) = 1.96), the identity of which was determined via its independent synthesis. Rates of the conversion 7 → 9 are shown to be dependent on the X–H bond strength of the H-atom donor, with a k(H)/k(D) = 4 when CD(3)OD is used in place of CH(3)OH as a solvent. A crystallographically characterized cis thiolate-ligated high-valent iron oxo, [Fe(IV)(O)(S(Me2)N(4)(tren))](+) (11), is shown to form en route to hydroxo 9. Electronic structure calculations were shown to be consistent with 11 being an S = 1 Fe(IV)=O with an unusually high ν(Fe–O) stretching frequency at 918 cm(−1) in line with the extremely short Fe–O bond (1.603(7) Å). |
