Acid catalysts are often used to increase reaction rates of organic transformations. These processes were traditionally completed using highly reactive metal-based Lewis acids. Iron, titanium, aluminum, and other first row transition metal complexes are strongly electron deficient which enables the catalysis of numerous reactions. Unfortunately, this enhanced reactivity comes with a price. These Lewis acids are often oxygen and water sensitive, require super-stoichiometric loadings, and are insoluble in nonpolar solvents.<br/><br/>To combat these drawbacks, we investigated incorporating electron deficient metal centers within a redox stable ligand framework. Some of the most widely studied electrochemically stable organometallic complexes utilize metallocene scaffolds. When oxidized, recent studies have shown ferrocene derivatives can exhibit multiple applications in organic synthesis. Members of this class of compounds have been recently used as mild one electron oxidants, electron donating co-catalysts, and relatively mild Lewis acids in a small number of studies.<br/><br/>In this work I will explain my adventure into expanding the usefulness of these redox stable metal complexes as oxygen and moisture tolerant, highly active, fully homogeneous catalysts. This presentation will describe ferrocenium derivatives as highly efficient catalysts for Friedel-Crafts and Diels-Alder reactions. These studies indicate that ferrocenium salts are useful homogeneous catalysts in non-polar media. Furthermore, these compounds are advantageous relative to traditional Lewis acids which are insoluble or overly reactive to the reaction conditions, or where modern organocatalysts require large catalyst loadings.

Charge-enhanced metallocene Lewis acids

ACS Spring 2022

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