The Fe<sup>III</sup>(H<sub>2</sub>O<sub>2</sub>) Complex
as a Highly Efficient Oxidant in Sulfoxidation Reactions: Revival
of an Underrated Oxidant in Cytochrome P450
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Abstract
This
work demonstrates that the Fe<sup>III</sup>(H<sub>2</sub>O<sub>2</sub>) complex, which has been considered as an unlikely oxidant
in P450, is actually very efficient in sulfoxidation reactions. Thus,
Fe<sup>III</sup>(H<sub>2</sub>O<sub>2</sub>) undergoes a low-barrier
nucleophilic attack by sulfur on the distal oxygen, <i>resulting
in heterolytic O–O cleavage coupled to proton transfer</i>. We further show that Fe<sup>III</sup>(H<sub>2</sub>O<sub>2</sub>) is an efficient sulfoxidation catalyst in synthetic iron porphyrin
and iron corrolazine compounds. In all cases, Fe<sup>III</sup>(H<sub>2</sub>O<sub>2</sub>) performs the oxidation <i>much faster
than it converts to Cpd I</i> and will therefore bypass Cpd I
in the presence of a thioether. Thus, this paper not only suggests
a plausible resolution of a longstanding issue in P450 chemistry regarding
the “second oxidant” but also highlights a new mechanistic
pathway for sulfoxidation reactions in P450s and their multitude of
synthetic analogues. These findings have far-reaching implications
for transition metal compounds, where H<sub>2</sub>O<sub>2</sub> is
used as the terminal oxidant
