Direct Observation of Primary C-H Bond Oxidation by an Oxido-Iron(IV) Porphyrin pi-Radical Cation Complex in a Fluorinated Carbon Solvent

Oxido-iron(IV) porphyrin pi-radical cation species are involved in a variety of heme-containing enzymes and have characteristic oxidation states consisting of a high-valent iron center and a pi-conjugated macrocyclic ligand. However, the short lifetime of the complex has hampered detailed reactivity studies. Reported herein is a remarkable increase in the lifetime (80 s at 10 degrees C) of Fe-IV(TMP+.)(O)(Cl) (2; TMP=5,10,15,20-tetramesitylporphyrin dianion), produced by the oxidation of Fe-III(TMP)(Cl) (1) by ozone in alpha,alpha,alpha-trifluorotoluene (TFT). The lifetime is 720 times longer compared to that of the currently most stable species reported to date. The increase in the lifetime improves the reaction efficiency of 2 toward inert alkane substrates, and allowed observation of the reaction of 2 with a primary C-H bond (BDEC-H=ca. 100 kcal mol(-1)) directly. Activation parameters for cyclohexane hydroxylation were also obtained.