In:
Chemistry – A European Journal, Wiley, Vol. 28, No. 52 ( 2022-09-16)
Abstract:
Saddle‐shaped hemes have been discovered in the structures of most peroxidases. How such a macrocycle deformation affects the reaction of Fe III hemes with hydrogen peroxide (H 2 O 2 ) to form high‐valent Fe‐oxo species remains uncertain. Through examination of the ESI‐MS spectra, absorption changes and 1 H NMR chemical shifts, we investigated the reactions of two Fe III porphyrins with different degrees of saddling deformation, namely Fe III (OETPP)ClO 4 ( 1 OE ) and Fe III (OMTPP)ClO 4 ( 1 OM ), with tert ‐butyl hydroperoxide ( t BuOOH) in CH 2 Cl 2 at −40 °C, which quickly resulted in O−O bond homolysis from a highly unstable Fe III ‐alkylperoxo intermediate, Fe III ‐O(H)OR ( 2 ) into Fe IV ‐oxo porphyrins ( 3 ). Insight into the reaction mechanism was obtained from [ t BuOOH]‐dependent kinetics. At −40 °C, the reaction of 1 OE with t BuOOH exhibited an equilibrium constant ( K a =362.3 M −1 ) and rate constant ( k =1.87×10 −2 s M− 〉 1 ) for the homolytic cleavage of the 2 O−O bond that were 2.1 and 1.4 times higher, respectively, than those exhibited by 1 OM ( K a =171.8 M −1 and k =1.36×10 −2 s −1 ). DFT calculations indicated that an Fe III porphyrin with greater saddling deformation can achieve a higher HOMO ([Fe(d ,d )‐porphyrin(a 2u )]) to strengthen the orbital interaction with the LUMO (O−O bond σ*) to facilitate O−O cleavage.
Type of Medium:
Online Resource
ISSN:
0947-6539
,
1521-3765
DOI:
10.1002/chem.202201139
Language:
English
Publisher:
Wiley
Publication Date:
2022
detail.hit.zdb_id:
1478547-X
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