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Dalton Transactions
Page 4 of 6
DOI: 10.1039/C8DT03519A
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Fig. 4. M06-L/def2-TZVP DFT results for the proposed reaction mechanism (1) involving the formation of 2-hydroxyflavanone through
H-atom abstraction from flavanone’s C2 by [FeIV(O)(N4Py)]2+ to form the enzyme-like product flavone.
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enzyme-like product flavone. A different pathway was also
investigated where the H-atom abstraction occurs at
flavanone’s C3 (cf. Fig. S21, ESI†), much higher energy barriers
were obtained (~30 and 18.5 kcal/mol for TS1 and TS2
respectively) rendering such pathway unfavorable compared
to the former. The second reaction mechanism entails a one-
step two H-atom abstractions leading to flavone + Fe2+ (H2O)
with no hydroxylation involved. This mechanism is shown in
Fig. S22 (ESI†). Abstraction of a second H-atom from flavanone
was found to cost ~40 kcal/mol, which (together with the
detection of 2-hydroxyflavanone as an experimental
intermediate) makes this reaction pathway unlikely.
,
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In this study we have demonstrated, that iron(II)
complexes with N4Py-type ligands are active and selective
catalysts in the oxidation of flavanone. The experimental and
computational results clearly indicated the formation of a
high-valent metal-oxo intermediate (FeIVO), and its role in the
oxidation process, including a rebound mechanism with the
formation of 2-hydroxyflavanone contrary with the
dissociation process suggested by Nam for substrates with
stronger C-H bonds.16 This system is the first biomimics of FS
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Notes and references
‡ Deposited CIF file: CCDC 1841256.
§ This work was supported by a grant from The Hungarian
Research Fund (OTKA) K108489, and GINOP-2.3.2-15-2016-
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