Diiron Bridged-Thiolate Complexes That Bind N_2 at the Fe^(II)Fe^(II), Fe^(II)Fe^I, and Fe^IFe^I 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.