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

• Published in: Angewandte Chemie International Edition 2019-08, Vol.58 (32), p.10863-10866
• Main Authors: Morimoto, Yuma, Shimaoka, Yuki, Ishimizu, Yuri, Fujii, Hiroshi, Itoh, Shinobu
• Format: Article
• Language: English
• Subjects: Alkanes; Anions; Cations; Cyclohexane; Fluorination; Heme; Hydrogen bonds; Hydroxylation; Iron; kinetics; Oxidation; porphyrinoids; reactive intermediates; Substrates
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201901608

Oxido‐iron(IV) porphyrin π‐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 π‐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 °C) of FeIV(TMP+.)(O)(Cl) (2; TMP=5,10,15,20‐tetramesitylporphyrin dianion), produced by the oxidation of FeIII(TMP)(Cl) (1) by ozone in α,α,α‐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. A lifetime: The short lifetimes of oxido‐iron(IV) porphyrin π‐radical cation species have hampered detailed reactivity studies of the complex. Reported here is the remarkably long lifetime (80 s at 10 °C) of FeIV(TMP+.)(O)(Cl) (TMP=5,10,15,20‐tetramesitylporphyrin dianion), produced by the oxidation of FeIII(TMP)(Cl) by ozone. The increased lifetime allows direct observation of the reactions of complex with a primary C−H bond.