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

Catechol and its derivatives are model compounds used to investigate the binding dynamics and photoinduced 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 O-2 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 O-2 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.