A dendritic TiO2–Co(ii) nanocomposite based on the melamine catalyzed one-pot aerobic photocatalytic synthesis of benzimidazoles.

A novel heterogeneous visible light active nanophotocatalyst was produced via modification of a nanocrystalline TiO₂ surface with a cobalt(ii) complex of melamine dendrimer under ultrasonic agitation, and was characterized by different techniques such as FT-IR, XPS, EDS, ICP-AES, TGA, DRS, UV-Vis, TEM and SEM. A red-shift of the band-edge and a significant reduction of the band-gap (2.7 eV) were revealed by UV-DRS. The as-prepared dendritic nanophotocatalyst significantly promoted the aerobic synthesis of benzimidazole derivatives with biological and pharmaceutical interest by a one-pot three-step process from the photooxidation of alcohols to aldehydes followed by cyclocondensation with 1,2-phenylenediamine with good to excellent yield. This process has the potential to enable a more sustainable benzimidazole synthesis. The combination of photocatalytic and catalytic reactions presented here may help to develop a new strategy towards the development of photocatalysis-based organic synthesis. [ABSTRACT FROM AUTHOR]