Photodriven Ammonia Synthesis from N2 and H2: Recycling of a Molecular Molybdenum Nitride

The synthesis of ammonia from its elements, N₂ and H₂, is the most atom-economical and thermodynamically preferred route but presents a high kinetic barrier and thus is rare using molecular compounds. Irradiation of a molecular molybdenum nitride prepared from N₂ cleavage with visible light in the presence of an iridium photocatalyst and 1-4 atm of H₂ produced high yields of ammonia along with the formation of a cationic, formally molybdenum(VI) pentahydride as the major molybdenum-containing product. Continued irradiation of the molybdenum hydride under an N₂ atmosphere resulted in regeneration of the molybdenum nitride that was recycled and used for additional hydrogenation to generate more ammonia, demonstrating superstoichiometric batch ammonia synthesis using only N₂ and H₂ with molecular compounds under ambient conditions.