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Direct hydroxylation of benzene and aromatics with H2O2 catalyzed by a self-assembled iron complex: evidence for a metal-based mechanism

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Abstract

An iminopyridine Fe(II) complex, easily prepared in situ by self-assembly of cheap and commercially available starting materials (2-picolylaldehyde, 2-picolylamine, and Fe(OTf)2 in a 2 : 2 : 1 ratio), is shown to be an effective catalyst for the direct hydroxylation of aromatic rings with H2O2 under mild conditions. This catalyst shows a marked preference for aromatic ring hydroxylation over lateral chain oxidation, both in intramolecular and intermolecular competitions, as long as the arene is not too electron poor. The selectivity pattern of the reaction closely matches that of electrophilic aromatic substitutions, with phenol yields and positions dictated by the nature of the ring substituent (electron-donating or electron-withdrawing, ortho-para or meta-orienting). The oxidation mechanism has been investigated in detail, and the sum of the accumulated pieces of evidence, ranging from KIE to the use of radical scavengers, from substituent effects on intermolecular and intramolecular selectivity to rearrangement experiments, points to the predominance of a metal-based SEAr pathway, without a significant involvement of free diffusing radical pathways.

Graphical abstract: Direct hydroxylation of benzene and aromatics with H2O2 catalyzed by a self-assembled iron complex: evidence for a metal-based mechanism

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Publication details

The article was received on 14 Sep 2017, accepted on 11 Oct 2017 and first published on 12 Oct 2017


Article type: Paper
DOI: 10.1039/C7CY01895A
Citation: Catal. Sci. Technol., 2017, Advance Article
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    Direct hydroxylation of benzene and aromatics with H2O2 catalyzed by a self-assembled iron complex: evidence for a metal-based mechanism

    G. Capocasa, G. Olivo, A. Barbieri, O. Lanzalunga and S. Di Stefano, Catal. Sci. Technol., 2017, Advance Article , DOI: 10.1039/C7CY01895A

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