Supramolecular Complex Assembly with Build-In Light-Harvesting Antenna Enables Efficient Photocatalytic Synthesis of Benzimidazoles

Abstract

ABSRACTMetal-polypyridine complexes are the fascinating transition-metal-ion-based photosensitizers in photocatalytic reactions, while, they often suffer from moderate photo-catalytic activity due to their low sunlight utilization efficiency and high carrier recombination rates. Herein, we employed the iron-terpyridine complex as the building block to develop a novel supramolecular complex assembly through π-π stacking interaction. The iron-terpyridine complexes served as a visible light harvesting center that harvested sunlight to generate electron-hole pairs. Furthermore, the π-π stacking mode is conducive to formation the fast electron transport pathway in supramolecular complex assembly, which thus enhances the charge separation efficiency. As a result, the obtained supramolecular complex assembly was highly efficient and universal in the photocatalytic Phillips-Ladenburg reaction of o-phenylenediamine and aromatic aldehydes, giving a wide range of benzimidazoles with almost quantitative yields (90-98%) in air under visible light irradiation at room temperature. Furthermore, the heterogeneous photocatalyst was highly stable and could be facilely recovered from the catalytic system for efficient reuse. These results provide a new method to enhance the light harvesting and charge separation of metal-polypyridine complexes through supremolecular assembly. It provides a high effective photocatalyst to achieve green synthesis of benzimidazoles under visible light irradiation.

Keywords: supramolecular complex assembly, iron-terpyridine complex, benzimidazoles, visible light photocatalysis, Phillips-Ladenburg reaction