Direct Evaluation of the Reactivity of Nonheme Iron(V)–Oxo Intermediates toward Arenes

The reactivity of nonheme iron­(V)–oxo intermediates toward aromatic C–H oxidation at −70 °C has been directly evaluated. The intermediates were generated upon the interaction of the ferric complex [(PDP*)­Fe^III(μ-OH)₂Fe^III(PDP*)]­(OTf)₄ (<b>4</b>^<b>◊</b>; PDP* = <i>N</i>,<i>N</i>′-bis­(3,5-dimethyl-4-methoxypyridyl-2-methyl)-(<i>S,S</i>)-2,2′-bipyrrolidine) with peracetic acid in the presence of acetic or 2-ethylhexanoic acid. The second-order rate constants (<i>k</i>₂) for the reaction of substituted benzenes with iron–oxo intermediates [(PDP*)­Fe^VO­(OC­(O)­R)]²⁺ at −70 °C were determined (R = CH₃, 3-heptyl). For more electron rich arenes, much higher <i>k</i>₂ values were observed, increasing in the order nitrobenzene < acetophenone < chlorobenzene < benzene < toluene, in accordance with the electrophilic aromatic substitution mechanism. The catalytic oxidation of mono- and dialkylbenzenes with H₂O₂ proceeded with good efficiency (up to 36.5 TN per Fe atom) and high selectivity toward aromatic oxidation products (up to 91%)