A Thiolate-Bridged Diiron Parent μ-Imide Involving as a Key Junction in the Bidirectional Interconversion Between Nitride and Amide.

Iron parent imides serve as key intermediates for iron-promoted nitrogen fixation and ammonia oxidation. However, these active species are difficult to be isolated, and their reactivities are underexplored. So far, only a few multinuclear iron parent imides were reported, but none plays a key intersection during the bidirectional transformation. Herein, we adopt the bulky 1,2,4-tri(tert-butyl)cyclopentadienyl (Cp') and bidentate 1,3-propanedithiolate (pdt) ligand to provide the steric protection for the reactive [Fe2S2] scaffold. As predicted, the highly active imido species can be captured by this [Fe2S2] platform to generate a novel thiolate-bridged diiron parent μ-imide complex 3. Mössbauer spectroscopy and DFT calculation reveal that 3 features a bent {FeIII-NH2--FeIII} framework with two anti-ferromagnetic coupled, low-spin Fe(III) centers. Importantly, imide 3 can not only undergo protonation to generate amide and finally release ammonia, but also go through hydrogen atom transfer to regenerate nitride. This reactivity indicates that 3 is a key junction that associates the late stage (N3- → NH2- → NH2 - → NH3) of nitrogen fixation and the initial period (NH2 - → NH2- → N3-) of ammonia oxidation. Overall, this work provides one available strategy that can stabilize a high-activity imide and investigate its reactivity of bidirectional interconversion.