Electrocatalytic N2 to N2H4 Conversion Using a Co(III) Dipyrrin-Dicarboxamide Complex

The selective electrocatalytic reduction of N₂ to N₂H₄ remains a formidable challenge in molecular catalysis. Very few homo-geneous systems have achieved this transformation selectively to date, yet they rely on multi-nuclear frameworks, harsh re-ductants, and photochemical biasing and exhibit low faradaic efficiency. Here, we report a Co(III) hexacoordinated dipyrrin-dicarboxamide complex, where a rare trianionic coordination mode featuring an anionic O donor from the amide enables selective N₂-to-N₂H₄ reduction at a monometallic Co center with a faradaic efficiency of ~22–24%. UV-vis and IR analyses, along with the demonstrated viability of chemical and electrochemical reduction, establish the two-electron-reduced formally Co(I) species as the catalytically active state. Spectroscopic and theoretical studies culminated in the proposal of a bent η¹-side-on N₂ binding mode via an interaction between the dz2 orbital and the π* of N2, which facilitates bent binding of the key diazeno and hydrazido(1-) intermediates, enhancing electron density on N leading to a superior N₂H₄ selectivity of 96% over NH₃. This work provides a blueprint for designing earth-abundant molecular catalysts with exceptional N₂H₄ selectivity.