Diiron Bridged-Thiolate Complexes That Bind N₂ at the FeᴵᴵFeᴵᴵ, FeᴵᴵFeᴵ, and FeᴵFeᴵ Redox States

All known nitrogenase cofactors are rich in both sulfur and iron and are presumed capable of binding and reducing N₂. Nonetheless, synthetic examples of transition metal model complexes that bind N₂ and also feature sulfur donor ligands remain scarce. We report herein an unusual series of low-valent diiron complexes featuring thiolate and dinitrogen ligands. A new binucleating ligand scaffold is introduced that supports an Fe(μ-SAr)Fe diiron subunit that coordinates dinitrogen (N₂-Fe(μ-SAr)Fe-N₂) across at least three oxidation states FeᴵᴵFeᴵᴵ, FeᴵᴵFeᴵ, and FeᴵFeᴵ). The (N₂-Fe(μ-SAr)Fe-N₂) system undergoes reduction of the bound N₂ to produce NH₃ (∼50% yield) and can efficiently catalyze the disproportionation of N₂H₄ to NH₃ and N₂. The present scaffold also supports dinitrogen binding concomitant with hydride as a co-ligand. Synthetic model complexes of these types are desirable to ultimately constrain hypotheses regarding Fe-mediated nitrogen fixation in synthetic and biological systems.