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Halogen Transfer to Carbon Radicals by High-Valent Iron Chloride and Iron Fluoride Corroles

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journal contribution
posted on 28.10.2021, 18:14 by Geoffrey W. Farley, Maxime A. Siegler, David P. Goldberg
High-valent iron halide corroles were examined to determine their reactivity with carbon radicals and their ability to undergo radical rebound-like processes. Beginning with Fe­(Cl)­(ttppc) (1) (ttppc = 5,10,15-tris­(2,4,6-triphenylphenyl)­corrolato3–), the new iron corroles Fe­(OTf)­(ttppc) (2), Fe­(OTf)­(ttppc)­(AgOTf) (3), and Fe­(F)­(ttppc) (4) were synthesized. Complexes 3 and 4 are the first iron triflate and iron fluoride corroles to be structurally characterized by single crystal X-ray diffraction. The structure of 3 reveals an AgI–pyrrole (η2–π) interaction. The Fe­(Cl)­(ttppc) and Fe­(F)­(ttppc) complexes undergo halogen transfer to triarylmethyl radicals, and kinetic analysis of the reaction between (p-OMe-C6H4)3C• and 1 gave k = 1.34(3) × 103 M–1 s–1 at 23 °C and 2.2(2) M–1 s–1 at −60 °C, ΔH = +9.8(3) kcal mol–1, and ΔS = −14(1) cal mol–1 K–1 through an Eyring analysis. Complex 4 is significantly more reactive, giving k = 1.16(6) × 105 M–1 s–1 at 23 °C. The data point to a concerted mechanism and show the trend X = F > Cl > OH for Fe­(X)­(ttppc). This study provides mechanistic insights into halogen rebound for an iron porphyrinoid complex.

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