(Invited) Electroanalytical Tools for Reaction Optimization and Mechanistic Investigation

Electroorganic chemistry is a multidisciplinary science that bridges the fields of electroanalytical chemistry and organic chemistry. From a synthetic perspective, its principal aim is to provide an environmentally benign alternative to classic organic synthesis by avoiding wasteful reagents. Electrochemistry may be considered as the most controlled way of transferring electrons with the possibility of finely tuning the value of electrode potential. Moreover, the current flowing through the electrode surface is an easy-to-measure quantity that offers a unique mechanistic tool for the study of the redox reactions and their coupled chemical reactions. Among the electroanalytical techniques voltammetric and amperometric techniques are the most popular ones. Cyclic voltammetry (CV) is the most widely used electrochemical technique for studying electrode processes. The flexible time window and forward and reverse scans of CV make it a powerful technique to study the mechanism of reactions that occur at an electrode surface. On the other hand, Chronoamperometry (CA) is another standard electrochemical technique that although contains less mechanistic information can be more straightforward to obtain quantitative information from electrochemical processes. In this talk, I will present a narrative of our recent progress in quantitative analysis of the electrode reactions, chemical redox reactions, and coupled chemical-electrochemical reactions using CV and CA techniques. The electrochemistry of iminoxyl and aminoxyl radicals will be discussed as showcase examples.^1,2 Electrochemical study of the aminoxyl catalyzed alcohol oxidation draw attention to a contrast between the use of electrochemical versus chemical methods for reoxidation of the catalysts during the course of the reaction.³ Under chemical conditions, the catalyst turnover is limited by the fixed oxidation potential of oxidant. Under electrochemical conditions, however, the oxidation rate is normalized by adjustment of the applied potential. Study of the imidoxyl and aminoxyl mediated C–H functionalization, via "hydrogen atom transfer" and "hydride transfer", highlights the advantages of low operational potential and minimal dependence on the substrate electronic properties for these electrochemical reactions.⁴ These features allow for functional‐group compatibility that is inaccessible with direct electrochemical oxidation. The insights from these electrocatalytic studies became the foundation for our efforts in implementing sustainable and scalable electrochemical oxidation reactions including alcohol oxidation, α‐oxygenations of cyclic carbamates and benzylic C–H iodination that will be discussed in this talk as well. 1. Nutting, J. E.; Rafiee, M.; Stahl, S. S. Chem. Rev. 2018, 118, 4834-4885. 2. Goes, S. L.; Mayer, M. N.; Nutting, J. E.; Hoober-Burkhardt, L. E.; Stahl, S. S.; Rafiee, M. J. Chem Educ. In Press. 3. Rafiee, M; Miles, K. C.; Stahl, S. S. J. Am. Chem. Soc. 2015, 137, 14751-14757. 4. Rafiee, M.; Wang, F.; Hruszkewycz, D. P.; Stahl, S. S. J. Am. Chem. Soc. 2018, 140, 22-25.