Photoisomerization of Azobenzene Induced Generation of Hydrazobenzene Mediated by Diboron Ester

Abstract

The reactions occurred at excited states are promising and flourished. Many strategies have been discovered reactions initiated by visible light and without transition metals and organic dyes. Diboron ester (B₂cat₂) has special activity towards unsaturated bonds at excited states. In this work, azobenzene and derivatives are reduced to hydrazo with high yield and high selectivity by a very convenient and rapid reaction. Only three factors, B₂cat₂, water and 400 nm lighting or sunlight are necessary. Density functional theory (DFT) studies and NMR results show that azobenzene is excited and a trans to cis isomerization occurs under 400 nm and B₂cat₂ reacts with cis azobenzene through B−B bond cleavage rather than with ground state trans azobenzene. Hydrazo compounds are obtained after hydrolysis with water. Gram level hydrazobenzenes are obtained under sunlight with moderate yields. This strategy is benefit to sustainable chemistry.