Highly Efficient Aromatic C−H Oxidation with H2O2 in the Presence of Iron Complexes of the PDP Family. Issue 18 (20th July 2018)

• Record Type: Journal Article
• Authors: Tkachenko, Nikolay V.; Ottenbacher, Roman V.; Lyakin, Oleg Y.; Zima, Alexandra M.; Samsonenko, Denis G.; Talsi, Evgenii P.; Bryliakov, Konstantin P.
• Is Part Of: ChemCatChem. Volume 10:Issue 18(2018)
• Page Start: 4052
• Page End: 4057
• Publication Date: 2018-07-20
• Subjects: Aromatic substitution -- hydrogen peroxide -- intermediates -- iron -- oxidation; Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.201800832
• Languages: English
• ISSNs: 1867-3880

Abstract

Abstract: The catalytic activity of a series of iron complexes of the PDP family (PDP=N, N′‐bis(2‐pyridylmethyl)‐2, 2′‐bipyrrolidine) in the oxidation of aromatic substrates with H2 O2 has been studied. In the presence of acetic acid, these complexes efficiently catalyze the oxidation of benzene and alkylbenzenes with high selectivity for oxygen incorporation into the aromatic ring (up to 93 %), performing up to 84 catalytic turnovers. The parent complex, [(PDP)(OTf)2 ], has demonstrated the highest catalytic efficiency and aromatic oxidation selectivity. The yield of products of oxidation of different substrates increases in line with increasing number of electron‐donating alkyl groups of the substrates: halogenbenzenes<benzene<monoalkylbenzenes<dialkylbenzenes, which, together with the results of competitive oxidation experiments and the observation of inverse primary k H / k D (0.90–0.92), agrees with the SE Ar oxidation mechanism. Low‐temperature EPR studies have witnessed the presence of low‐spin ( g 1 =2.071, g 2 =2.008, g 3 =1.960) perferryl intermediates, demonstrating direct reactivity toward benzene. The oxidation of m ‐xylene in the presence of H2 18 O has shown the same probability of 18 O incorporation into the aromatic ring and the aliphatic moieties, which is indicative that both the aromatic and aliphatic oxidations are conducted by the same active species. Abstract : Bioinspired iron complexes catalyze the oxidation of benzene and alkylbenzenes with H2 O2, with high efficiency and selectivity for aromatic oxidation. Catalytic, mechanistic and spectroscopic data bear evidence in favor of the electrophilic aromatic substitution mechanism, driven by perferryl species.