Visible light photocatalysis of dye-sensitized TiO2: The selective aerobic oxidation of amines to imines

Herein, we report an efficient protocol for the selective oxidation of amines with the sole involvement of conduction band electrons (e cb − ) of TiO 2 for both the activation of O 2 and the ensuing oxidation reaction. Visible light was harvested by dye molecules on the surface of TiO 2 , which injects electrons into its conduction band, generating dye radical cations. Charge transfers from dye radical cations to amines are relayed by the catalytic cycle of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to TEMPO + , which is an oxidant that can conduct the direct two-electron oxidation of amines to imines. TEMPO was regenerated by the oxidation of TEMPOH with superoxide generated by the interaction of e cb − and O 2 . This work suggests that one can exploit the strategy of cooperative photocatalysis with each component performing in its optimal role: TiO 2 for O 2 activation, dye for visible light harvesting, and TEMPO for oxidative transformations.