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 2019-08, Vol.131 (32), p.10979-10982
• Main Authors: Morimoto, Yuma, Shimaoka, Yuki, Ishimizu, Yuri, Fujii, Hiroshi, Itoh, Shinobu
• Format: Article
• Language: English
• Subjects: Alkanes; Anions; Cations; Chemistry; Cyclohexane; Eisen; Fluorination; Heme; Hydrogen bonds; Hydroxylation; Iron; Oxidation; Oxidationen; Porphyrinoid; Reaktionskinetik; Reaktive Zwischenstufen; Substrates
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.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. Die kurzen Lebensdauern von Oxidoeisen(IV)‐Porphyrin‐π‐Radikalkationen haben detaillierte Reaktivitätsstudien der Komplexe erschwert. Hier wird über die bemerkenswert lange Lebensdauer (80 s bei 10 °C) von FeIV(TMP+.)(O)(Cl) (TMP=5,10,15,20‐Tetramesitylporphyrin dianion) berichtet, das durch Oxidation von FeIII(TMP)(Cl) durch Ozon entsteht. Die erhöhte Lebensdauer ermöglicht die direkte Beobachtung der Reaktionen des Komplexes mit einer primären C‐H‐Bindung.