Selective photocatalytic reduction of nitrobenzene to anilines, azoxybenzene, and azobenzene: a solvent-dependent and light-induced process mediated by a CdS/NH₂-MIL-125 nanocomposite

While photocatalytic selective transformations have advanced significantly, selective reduction reactions remain less developed. This study investigated the photocatalytic reduction of nitrobenzene using a previously characterized CdS/MOF photocatalyst, focusing on the selective formation of aniline, azoxybenzene, and azobenzene. It was found that various parameters, mostly the solvent and base, strongly affect reaction selectivity. Employing hydrazine as a hydrogen source, we achieved high yields and selectivity for aniline in methanol, azoxybenzene in tetrahydrofuran, and azobenzene in ethanol. Notably, the presence of K₂CO₃ proved critical for obtaining high selectivity towards azobenzene. We successfully extended the reaction scope to produce various anilines and azobenzene derivatives from their corresponding aromatic nitro compounds, obtaining the desired products in moderate to good yields. The CdS/MOF photocatalyst exhibited good reusability, maintaining a high yield and selectivity over several cycles with only a slight decrease in performance.