Ammonia synthesis by photocatalytic hydrogenation of a N₂-derived molybdenum nitride

Although metal complexes are known to split dinitrogen at ambient temperature and pressure, the synthesis of ammonia from these compounds with H₂ as the terminal reductant is rarely achieved. Here we report a photocatalytic ammonia synthesis from a N₂-derived terminal molybdenum nitride by using H₂ as the terminal reductant. An iridium hydride photocatalyst mediates the reaction on irradiation with blue light. A molybdenum pentahydride was identified as the principal metal product to arise after ammonia release. Conversion of the molybdenum pentahydride back to the terminal molybdenum nitride was accomplished in three steps and completed a synthetic cycle for NH₃ formation from N₂ and H₂. Mechanistic investigations support a pathway that involves photoexcitation of the iridium hydride and a subsequent energy transfer rather than electron transfer. Deuterium labelling confirmed H₂ as the source of the N–H bonds. This photodriven, proton-coupled electron transfer allows the use of H₂ as the terminal reductant for the catalytic formation of NH₃ from N₂ using metal catalysts. [Figure not available: see fulltext.]