Mechanistic study for the selective oxidation of benzene and toluene catalyzed by Fe(ClO4)(2) in an H2O2-H2O-CH3CN system

Abstract

Iron(II) perchlorate in an H2O-H2O2-CH3CN mixture was used to efficiently carry out C-H bond activations of benzene to form phenol and/or hydroquinone, and of toluene to form benzaldehyde, benzyl alcohol, o-cresol, p-cresol, and/or methyl-p-benzoquinone. The reactions were facilely tuned and controlled to selectively yield either a single or double oxygenation of benzene as well as a sp(3) or sp(2) C-H bond oxidation of toluene. On the basis of HAD kinetic isotope effect data, we determined the aromatic oxidation to mostly proceed by way of formation of an arene oxide or a sigma-complex intermediate from high-valence iron species and to then undergo a 1,2-hydride shift, i.e., NIH-shift rearrangement. (C) 2017 Elsevier B.V. All rights reserved.