Nitrogenases are the only enzymes known to catalyze the reduction of dinitrogen to ammonia, and their active sites consist of clusters containing belt irons ligated by sulfides and the only known biological carbide. Synthetic iron complexes are useful in examining structures and elementary reactions that may be relevant to enzymatic function. To mimic the coordination sphere of the enzyme active site, we report iron complexes with new ligand scaffolds featuring anionic C and S donors (SCS and PCS pincers). Reactivity with nitrogenase-relevant amide, thiolate, NH<sub>3</sub>, and CO ligands is demonstrated, and several electronic structures are accessible. The SCS pincer has a proton-responsive thioamide site whose protonation state modulates the reduction potential of iron. Though both ligands coordinate through anionic C and S, their differing abilities to support various iron spin and oxidation states allow us to test how these factors influence the binding and reactivity of nitrogenase substrates.

Mixed carbon and sulfur-based ligands for synthetic modeling of nitrogenase

ACS Spring 2022

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