Nitride-incorporated W-Fe-S double cubane clusters: terminal ligand substitutions and redox behaviors.

Structural mimicking of the nitrogenase FeMo cofactor has long been a challenge in synthetic inorganic chemistry and bioinorganic chemistry. This already very tough task had become even harder after the discovery of an interstitial light atom, which was later evidenced to be carbide. From a synthetic point of view, to introduce such a 2p atom into the core of a Fe-S cluster would have to overcome the coordination competition from overwhelming sulfide ligands. Recently, we have reported a controlled synthetic strategy named redox metathesis based on template-assisted structure design, and have successfully synthesized a couple of nitride-incorporated edge-bridged double cubane (N-EBDC) W-Fe-S clusters. In this work, we have systematically studied the terminal ligand substitutions of heteroleptic N-EBDC clusters, utilizing ethanethiolate, thiophenolate, p-thiocresolate, azide, and methoxide to replace the terminally bound chloride ligands. Structural analysis of this family of N-EBDC clusters reveals that different terminal ligands affect the fine structures of the cluster cores at different levels. Further studies by cyclic voltammetry indicate that these N-EBDC clusters with distinct terminal ligands exhibit different redox behaviors, furnishing in-depth information on the electronic structure of these clusters potentially related to their reactivity. This study provided useful information for the investigation of nitrogenase related Fe-S clusters toward structural and functional mimicking of the nitrogenase FeMo cofactor.