Photocatalytic activity of asymmetric cobalt thioporphyrazine for selective aerobic oxidation of amines under visible light

The development of highly efficient visible-light-driven photocatalysts based on metallothioporphyrazines has recently attracted significant attention for solar energy utilization. In this work, a novel asymmetric cobalt 19,22-bis(butyloxy)-4,5,9,10,14,15-hexakis(butylthio)porphyrazine (denoted as C1) was synthesized through the magnesium template method using 2,3-bis(butylthio)maleonitrile and 3,6-dibutoxyphthalonitrile as precursors. Significantly, the asymmetric C1 exhibited superior photogenerated charge separation capability compared to the symmetric cobalt octakis(butylthio)porphyrazine (denoted as C2), which was testified by photoluminescence spectrum, photocurrent response and electrochemical impedance spectrum. When serving as a visible-light-driven photocatalyst, C1 can selectively oxidize amines to their corresponding imines under visible light (λ ≥ 420 nm) irradiation using atmospheric O 2 as the oxidant, displaying higher photocatalytic activity than C2. Reactive oxygen species including singlet oxygen ( 1 O 2 ) and superoxide anion radical (O 2 •- ) participated in the photocatalytic oxidation reaction, which were confirmed by active species quenching experiments and electron spin resonance (ESR) measurements. Hammett plot analysis indicated the involvement of a carbocation intermediate in the photocatalytic process. This work provides a new strategy for amine oxidation and highlights the significant potential of asymmetric metallothioporphyrazines as visible-light-driven photocatalysts for organic synthesis.