In Situ Generated Bimetallic Nanoparticle Catalysts for the Transfer Semihydrogenation of Azoarenes

Hydrazoarenes are important structural components extensively utilized across diverse industries, such as dyes and pharmaceuticals; they are also vital in supramolecular chemistry for the synthesis of highly substituted aniline derivatives. Although the semihydrogenation of azoarenes is a common method for hydrazoarene synthesis, developing an efficient and selective semihydrogenation method remains challenging. Bimetallic nanoparticle catalysts present a promising avenue for enhancing these hydrogenation reactions through the synergistic effects of two metals, potentially enhancing the catalytic activity or selectivity. However, determining the optimal metal combination for maximizing the synergistic effects in azoarene semihydrogenation poses a significant challenge. In this study, we present an innovative approach for in situ generation of bimetallic nanoparticle catalysts for the transfer semihydrogenation of azoarenes. This method involves the straightforward generation of bimetallic nanoparticles by adding ammonia borane (NH3BH3) to an ethanol solution containing two metal salts. Among the various bimetallic catalysts investigated, NiZn (a combination of Ni and Zn salts) exhibited the highest activity and selectivity for the semihydrogenation reaction, enabling the selective reduction of various azoarenes to their corresponding hydrazoarenes under mild reaction conditions. The proposed method offers an efficient catalytic system for the transfer semihydrogenation of azoarenes.