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Redox Switchable Catalysis

Catalysis is employed by both natural and artificial processes in order to transform efficiently building blocks, which are readily available, into molecules and materials with high value and function. Nature has evolved several mechanisms that allow enzymatic syntheses to occur in parallel within cells. In order to avoid unwanted interference from other reaction pathways, enzyme activity is controlled spatially and temporally; this control is often modulated through feedback loops and a variety of trigger-induced effects, known as allosteric control. In contrast, the reactions promoted by man-made catalysts usually occur according to carefully chosen reaction conditions. As such, research in this field has largely focused on the invention of new catalysts and the optimization of their performance to achieve high conversions and/or selectivity. Recently, however, chemists have been drawing more and more inspiration from nature and have started to look at catalytic processes that can be switched by an external stimulus. Incorporating stimuli-responsive features into artificial catalysts can confer an additional, ‘bio-like’ level of control over chemical transformations, with the goal that such systems will perform tasks in synthesis that are difficult or impossible to accomplish in other ways. Potential applications include using the states of multiple switchable catalysts to control sequences of transformations, producing different products from a pool of building blocks according to the order and type of stimuli applied, similar to the natural occurrence of multiple enzymatic processes in the cells.

The Diaconescu Group became interested in redox switchable catalysis, which uses redox reagents (chemical triggers) to turn on and off reactions, because of previous work with metal complexes supported by ferrocene-based ligands, which are redox active. Metal complexes containing redox-switchable groups are increasingly studied since these groups provide a method to alter the electronic properties of a metal center without the need for excessive, additional synthetic steps to achieve ligand modification. Because both species in redox-switchable catalysis originate from a single precursor, the cost of chemical synthesis is greatly reduced. One method to modulate reactivity and selectivity is through the redox control of the supporting ligand in a metal complex. Ferrocene has been used as a redox switch in various fields due to both its robustness and the versatility of procedures known for the synthesis of ferrocene derivatives. The goal of this research is to design catalysts that exhibit orthogonal reactivity for different substrates by switching between the oxidized and reduced forms of a metal complex. Ultimately, this project is pushing the boundaries of understanding the factors that influence catalytic activity.