Iron oligopyridine complexes as efficient catalysts for practical oxidation of arenes, alkanes, tertiary amines and N-acyl cyclic amines with Oxone

Abstract

The iron complexes [Fe(qpy)](ClO₄)₂ (1) (qpy = 2, 2′ : 6′, 2′′ : 6′′, 2′′′ : 6′′′, 2′′′′-quinquepyridine), [Fe₂(spy)₂](ClO₄)₄ (2) (spy = 2, 2′ : 6′, 2′′ : 6′′, 2′′′ : 6′′′, 2′′′′: 6′′′′, 2′′′′′-sexipyridine), [Fe₂(septipy)₂](ClO₄)₄ (3) (septipy = 2, 2′ : 6′, 2′′ : 6′′, 2′′′ : 6′′′, 2′′′′ : 6′′′′, 2′′′′′ : 6′′′′′, 2′′′′′′-septipyridine) and SBA-15-supported iron terpyridine complex (4) are efficient catalysts for the practical oxidation of alkenes, arenes, alkanes, tertiary amines and N-acyl cyclic amines using Oxone as the oxidant. With 1, 2, 3 or 4 as the catalyst, a variety of electron-rich and electron-deficient alkenes were oxidized to the corresponding epoxides in high isolated yields (up to 99%). The reaction of arenes with Oxone afforded quinones in up to 91% isolated yields. Selective C–H bond oxidation of saturated alkanes to alcohols/ketones and demethylation of tertiary amines to secondary amines were achieved in good product yields. For the oxidation of N-acyl cyclic amines, the ring-opened products were obtained in up to 75% isolated yield with up to 96% substrate conversion. All of these iron complexes can efficiently catalyse the oxidative C–C bond cross-coupling reaction of tertiary amines with NaCN in up to 86% isolated yield using (^tBuO)₂ as the terminal oxidant. The oligopyridine ligands were oxidatively robust and could be re-used by the addition of iron(II) salt to generate the iron catalystsin situ. The active SBA-15-supported terpy ligand could be re-used for the oxidative catalysis for five consecutive runs without significant loss of catalytic activity.