Platinum(II) Schiff Base Complexes as Photocatalysts for Visible-Light-Induced Cross-Dehydrogenative Coupling Reactions

Four phosphorescent platinum(II) Schiff base complexes are screened for application in visible-light-induced cross-dehydrogenative coupling (CDC) reactions. Preliminary studies show that, among the four platinum(II) complexes, Pt3 is an efficient catalyst for CDC reactions with oxygen as an oxidant. Light irradiation (lambda > 420 nm) on a mixture of the PtII complex, tertiary amine, and a variety of nucleophiles (nitroalkanes, ketones, or indoles) under aerobic conditions gives alpha-functionalized tertiary amines in good to excellent yields. The photoluminescence quenching experiment reveals that the CDC reaction is initiated by photoinduced electron transfer from N-phenyltetrahydroisoquinoline to the Pt-II complex. Further, electron spin resonance (ESR) measurements clearly indicate the formation of superoxide radical anions (O-2(center dot-)) rather than singlet oxygen (O-1(2)) during the photocatalytic reaction.