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

摘要

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(μ-SAr)Fe diiron subunit that coordinates dinitrogen (N_2-Fe(μ-SAr)Fe-N_2) across at least three oxidation states (Fe^(II)Fe^(II), Fe^(II)Fe^I, and Fe^IFe^I). The (N_2-Fe(μ-SAr)Fe-N_2) system undergoes reduction of the bound N_2 to produce NH_3 (∼50% yield) and can efficiently catalyze the disproportionation of N_2H_4 to NH_3 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.