Visible-light-responsive polyoxometalate-based metal–organic framework for highly efficient photocatalytic oxidative coupling of amines

Abstract

The exploration of new highly efficient and durable for the oxidation of amines to imines has gained immense attention. In this work, a new polyoxometalate-based metal–organic framework (POMOF) {Cu4(C26H16N4O4)4(CH3CN)2[SiW12O40]}·4H2O (SiW-Cu-DPNDI) was constructed with a catalytic oxidant Keggin-type [SiW12O40]4− anion, a photosensitizer N,N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI) ligand, and a Cu(I) cation via self-assembling. Although single-crystal X-ray diffraction, power X-ray diffraction (PXRD), infrared (IR) spectroscopy, etc., were employed to confirm the hierarchical structure of SiW-Cu-DPNDI, critical analyses through, such as the magnetic susceptibility measurements, the Mott–Schottky measurements, and the electron spin resonance studies were successfully applied to elucidate the properties of POMOF. SiW-Cu-DPNDI was highly active in the heterogeneous photocatalysis of the oxidation of amines to imines under mild conditions. Additionally, this catalyst exhibited high stability and reusability without losing its activity during the photocatalysis. The possible mechanism of the oxidation coupling was extensively investigated under visible-light (Vis)-irradiation.