Iron–sulfur enzymes catalyze a diverse set of challenging chemical reactions and are in particular utilized for a variety of multi-electron redox reactions. In many cases, substrates interact directly with one or more of the iron sites of the Fe–S cluster; controlling these interactions requires the enzyme to precisely manipulate the coordination sphere of each Fe center. Achieving similar reactibity using synthetic Fe–S clusters requires establishing a comparable level of control over Fe coordination chemistry, however this is significantly more challenging in the absence of a protein scaffold. Synthetic Fe–S clusters undergo a number of reactions that are typically prevented in a protein environment: oligomerization to form higher nuclearity clusters, disproportionation to form homoleptic clusters, and uncontrolled ligand substitution and redistribution leading to mixtures of clusters with different numbers of new ligands bound. Additionally, protein active sites provide steric control over the binding pocket at the unique Fe, which is difficult to achieve in synthetic systems. To solve these problems, it is necessary to develop a ligand system in which the ligands on the remote Fe sites provide steric protection for the unique Fe site, and in which intermolecular decomposition processes are disfavored. We demonstrate that diaryl <i>N</i>-heterocyclic carbenes (NHCs) fulfill these requirements—the steric profile of the NHC ligands dictates how many can bind to the cluster, shutting down decomposition pathways observed with less sterically encumbering ligands and providing access to clusters that are robust towards ligand redistribution and disproportionation. Additionally, the tunability of NHCs allows for precise control over the steric environment of the unique Fe site, and this has enabled the synthesis of Fe–S clusters bound to a variety of substrates. Studies of these novel clusters will be a primary focus of the talk.

Coordination chemistry of Fe–S clusters dictated by remote steric effects

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ACS Fall 2022

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