Ligand-to-metal charge transfer of a pyridine surface complex on TiO2 for selective dehydrogenative cross-coupling with benzene

Abstract

Dehydrogenative cross-coupling (DCC) between pyridine and benzene proceeded selectively using a TiO₂ photocatalyst under visible light irradiation at optimized concentrations of the substrates. Visible light induces ligand-to-metal charge transfer (LMCT) between pyridine and a TiO₂ surface to give a pyridine radical cation, which produces a pyridyl radical by its deprotonation or oxidation of another pyridine molecule. The pyridyl radical attacks a benzene ring to form an sp²C–sp²C bond and a hydrogen atom is subsequently removed to complete DCC. Selective excitation of the pyridine LMCT complex in the presence of an excess amount of benzene would be the key for higher selectivity.