Poster Presentation 21st International Conference on Biological Inorganic Chemistry 2025

Catalytic nitrogen reduction reaction (N₂RR) is an important chemical transformation in both biology and industry, enabling the conversion of inert atmospheric N₂ into valuable nitrogen-containing compounds, such as ammonia (NH₃) and hydrazine (N₂H₄). Our group has demonstrated that tris(phosphino)borane-bound iron complexes can act as well-defined platforms for catalytic N₂ fixation to produce ammonia or hydrazine, where the product selectivity can switch by the choice of proton (H⁺) and electron (e⁻) sources.^1,2 In this work, we showcase an iron catalyst design strategy that enables the selective N₂-to-N₂H₄ conversion under protic conditions. The incorporation of cationic trimethylammonium (NMe₃⁺) groups into the tris(phosphino)borane ligand framework produces Fe-precatalysts that operate efficiently in methanol. The newly prepared iron catalysts achieved hydrazine-selective N₂ fixation with high yields (up to >20:1 N₂H₄:NH₃ selectivity, 73% yield). Computational analyses reveal that these ligand modifications significantly shift the reduction potential of Fe–hydrazido intermediates anodically, which is a key branch point for hydrazine versus ammonia selectivity.³