The critical roles of iron-sulfur (Fe-S) and molybdenum cofactor enzymes in biochemical processes have long intrigued scientists. This work delves into the construction of synthetic models that provide insight into the complex reactions these enzymes facilitate, particularly focusing on the reactivity of Fe-S clusters with nitric oxide (NO) and the catalytic applications of synthetic model of Mo enzyme. Iron−sulfur clusters are susceptible to damage from redox reactions with reactivity nitrogen species (NO) and reactive oxygen species (like O2), which can lead to cluster interconversion or partial or complete loss of iron. In this work, I’ll show a [4Fe-4S] model system that is capable of releasing bridging sulfides as H2S upon nitrosylation in the presence of thiol. The iron-nitrosyl products of this reaction were identified as DNIC and a RBA-like intermediate. These results suggest that [Fe-S] clusters are likely to be a site for the crosstalk between NO and H2S in biology. Furthermore, our research reveals that the repair of damaged [Fe-S] clusters is achievable through biological mechanisms. Biophysical and biochemical studies showed the presence of cysteine persulfide during the cluster repair in FNR and Fdx, but the mechanism of the persulfide-mediated repair remains unknown. In our study, we investigate the reactivity of in-situ generated organic persulfides with a series of ferric and ferrous iron complexes supported by N,N’-Ethylenebis(salicylimine) (salen) and its analogs. The mononuclear [FeII(salen)] and [FeIII(salen)Cl] complex are converted to a µ-sulfidyl dimer species, [FeIII(Salen)]2S. This discovery suggests that cellular persulfides may play a pivotal role in repairing damaged [Fe-S] clusters within cells by acting as a source of bridging sulfide. In the context of synthetic models of Mo enzymes, we synthesized a series of μ-oxo Mo(V) thiosemicarbazone complexes, incorporating various substituents at the para-phenyl position. This effort aimed to investigate their catalytic sulfur atom transfer (SAT) reactivity. SAT chemistry has proven its utility in industrial processes; however, sulfur atom transfer systems are scarce and highly sought after. Our research unveiled that the incorporation of electron-withdrawing nitro or bromo groups significantly enhances turnover rates compared to the electron-donating methoxy group. This trend led us to propose a catalytic mechanism akin to previously reported oxygen atom transfer reactions, involving a [MoVI(O)(E)]2+ (E = O, S) intermediate.
