Decoupling Electron and Proton Transfer in Noncontact Catalytic Hydrogenation of Nitroaromatics

Understanding the elementary reactions of active hydrogen species and electron transfer mechanisms during catalytic hydrogenation remains a fundamental challenge. This work elucidates electron and proton transfer pathways in nitroaromatics hydrogenation using a noncontact catalytic system. Strong coordination of (hypo)phosphorous acid on Pt/Pd surfaces prevents substrate adsorption while permitting H2 activation, generating electrons retained on the catalyst and protons solvated in protic solvents. Hydrogenation proceeds via sequential reduction (nitro to nitroso and then to hydroxylamine), governed primarily by electron transfer through conductive carbon supports and secondarily via catalyst interfaces, while proton transfer occurs through protic solvents. Disproportionation dominates hydroxylamine conversion due to its kinetic superiority over direct hydrogenation. By applying these mechanistic insights, the system is expanded to diverse catalysts, demonstrating that hypophosphorous acid-modified commercial Pt/C catalyst achieves efficient nitroaromatics hydrogenation. Remarkably, this approach functionally mimics enzymatic catalysis, enabling selective hydrogenation of coenzyme Q10 and its analogues. This study advances fundamental understanding of hydrogenation mechanisms of nitroaromatics, carbon-supported catalyst design, and enzyme-mimetic catalysis development.