Merging the catechol–TiO2 complex photocatalyst with TEMPO for selective aerobic oxidation of amines into imines

Abstract

Catechol and its derivatives are model compounds used to investigate the binding dynamics and photo-induced interfacial charge transfer events between an organic molecule and TiO₂. However, the practical potential of this process has received little attention in part due to the conceived instability of these molecules on TiO₂ under light irradiation. Herein, we present a new paradigm for selective oxidation of amines into imines with atmospheric O₂ by exploring the surface complexation of catechol derivatives on TiO₂ which gives rise to visible-light-induced events of charge transfer. Our success depends on the merger of visible light photocatalysis of catechol surface-complexed TiO₂ with TEMPO catalysis. With 5 mol% of TEMPO as the co-catalyst and the catechol–TiO₂ complex (containing 0.8 mol% of catechol) as the photocatalyst, amines can be efficiently oxidized into imines with atmospheric O₂ under irradiation of blue light emitting diodes. Our work suggests that a suitable co-catalyst is the key to significantly expand the scope of visible light photocatalysis for selective chemical transformations.