A High-Valent Iron-Oxo Corrolazine Activates C-H Bonds via Hydrogen-Atom Transfer

Oxidation of the Fe-III complex (TBP(8)Cz)Fe-III [TBP(8)Cz = octakis(4-tert-butylphenyl)corrolazinate] with O-atom transfer oxidants under a variety of conditions gives the reactive high-valent Fe(O) complex (TBP(8)Cz(+center dot))Fe-IV(O) (2). The solution state structure of 2 was characterized by XAS [d(Fe-O) = 1.64 angstrom]. This complex is competent to oxidize a range of C-H substrates. Product analyses and kinetic data show that these reactions occur via rate-determining hydrogen-atom transfer (HAT), with a linear correlation for log k versus BDE(C-H), and the following activation parameters for xanthene (Xn) substrate: Delta H-double dagger = 12.7 +/- 0.8 kcal mol(-1), Delta S-double dagger = -9 +/- 3 cal K-1 mol(-1), and KIE = 5.7. Rebound hydroxylation versus radical dimerization for Xn is favored by lowering the reaction temperature. These findings provide insights into the factors that control the intrinsic reactivity of Compound I heme analogues.