Electrocatalytic Reduction of Nitrogen to Ammonia Using a Trinuclear Nickel Thiolate Complex

Activation and reduction of N₂ to NH₃ are a formidable challenge. While there have been several reports of metal complexes that can bind and activate N₂, very few catalysts have been reported to catalyze the electrochemical reduction of N₂ to NH₃ selectively, under ambient conditions, and with reasonable yields. A trinuclear Ni complex with a bulky thiolate ligand and a boat-shaped cavity is synthesized and characterized. This complex can electrocatalytically reduce N₂ selectively by 6e^-/6H⁺ to NH₃ using phenol as a proton source with a Faradaic yield of >80% at -2.3 V vs Fc^+/0 in CH₃CN solvent. The selective 6e^-/6H⁺ reduction of N₂ contrasts with a previous report of an analogous complex with propanethiolate ligands that could reduce N₂ by 4e^-/4H⁺ to N₂H₄.