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 N-2. Nonetheless, synthetic examples of transition metal model complexes that bind N-2 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(mu-SAr)Fe diiron subunit that coordinates dinitrogen (N-2-Fe(mu-SAr)Fe-N-2) across at least three oxidation states ((FeFeII)-Fe-II, (FeFeI)-Fe-II, and (FeFeI)-Fe-I). The (N-2-Fe(mu-SAr)Fe-N-2) system undergoes reduction of the bound N-2 to produce NH3 (similar to 50% yield) and can efficiently catalyze the disproportionation of N2H4 to NH3 and N-2. 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.