Visible-Light-Driven C-N Bond Formation by a Hexanickel Cluster Substituted Polyoxometalate-Based Photocatalyst

A powerful and attractive route to develop novel photocatalysts for C-N bond formation involves the use of pyrrolidine as the substrate and cocatalyst simultaneously. Herein, a new polyoxometalate (POM)-based metal-organic framework, namely, [Ni₆(OH)₃(H₂O)₉(DPNDIH)(SiW₉O₃₄)]₂·2H₂O (SiW₉Ni₆-DPNDI) (DPNDI = N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide), was prepared by incorporating a Ni₆ cluster-substituted POM anion and a photosensitizer (DPNDI) into a framework. The anion···π interactions and covalent bonds between SiW₉Ni₆ and DPNDI are beneficial for the consecutive electron separation and transfer. Under visible-light irradiation, DPNDI can be easily excited to generate radical species DPNDI* that could be further excited in the presence of the electron donor pyrrolidine for the inert O₂ activation. SiW₉Ni₆-DPNDI showed a high efficiency in the photocatalysis of C-N bond formation under a mild condition by the synergy of DPNDI and SiW₉Ni₆. The results of the reaction were confirmed by gas chromatography and ¹H NMR. In addition, SiW₉Ni₆-DPNDI exhibited a high sustainability without an obvious change in yields after five cycles.