Anodic Cyclization Reaction: Manipulation of Reaction Pathway and Efforts to Radical Cation and Radical Intermediate

In recent years, synthetic chemists have been expressing significant interest in electro-organic synthetic methods. This interest is being fueled by the existence of an increasing number of successful methods in the literature and the availability of new electrochemical equipment that removes the barrier to attempting an electrolysis reaction for the first time. Yet while these developments have fueled growth in some areas of electro-organic synthesis (the recycling of chemical catalysts for example), other areas remain underdeveloped. One such area is the exploration of reactions that can be triggered directly as an electrode surface without the use of any chemical reagent. Such reactions lead to highly reactive intermediates that allow for entirely new modes of reactivity to be explored. For example, our group has been working to develop anodic oxidation reactions that convert electron rich olefins into reactive radical cation intermediates. The reactions lead to a reversal in the polarity of the original olefin that enable the normally nucleophilic groups to be used as electrophiles. The result is an opportunity to change the entire manner in which the synthesis of a complex target is approached. Simply put, new modes of reactivity offer an opportunity to not only change the way individual steps in a synthetic sequence are conducted but also change the overall route because groups that normally function in a certain manner no longer behave the same way. While efforts to demonstrate the power of these opportunities have been successful for a variety of reactions in the group, our ability to continue forwarding the chemistry into even newer areas relies on our continuing to expand our knowledge of the reactive intermediates involved in electrochemical oxidation reactions, how they behave, and how they can be channeled down productive pathways. With this in mind, the main focus of this dissertation is to build our understanding of the reactive intermediates involved in anodic cyclization reactions and how those intermediates can best be applied as synthetic tools. The work probes the advantage of directly using the radical cations intermediates generated at an anode for triggering bond formation relative to pushing the reactions away from pathways that utilize the radical cation and toward pathways that involve an oxidative radical pathway. Along these lines, a synthetic route that allows both pathways to be accessed from the same starting materials has been developed. Using the chemistry, reactions that generate seven membered ring products and oxidative tandem cyclization reactions have been explored. In addition to these studies, an example of how optimizing a reaction sometimes requires one to pay attention to intermediates downstream of the cyclization is reported. Finally, the electrochemical method has been extended to an example of how it can be used in the synthesis of a complex molecular surface

High-throughput solubility determination for data-driven materials design and discovery in redox flow battery research

Solubility is crucial for redox flow batteries as it affects their energy density. A data-driven approach based on AI/ML models can speed up the development of highly soluble redox active materials, but accurate solubility prediction remains elusive because of the lack of relevant databases. To overcome this deficiency, we developed a high-throughput experimentation process that combines a robotically controlled platform with high-throughput methodology to collect large-scale and high-quality solubility data. We demonstrate the potential utility and applicability of this high-throughput process by measuring the aqueous and non-aqueous solubilities of redox active materials and studying the effect of additives on their solubilities for both aqueous and non-aqueous redox flow battery applications. A redox flow battery based on our optimized negative electrolyte formulation and ferrocyanide positive electrolyte offers highly stable performance over 18 days (>100 cycles) with consistent capacity and a 24% boost in energy density

Reversible redox chemistry in azobenzene-based organic molecules for high-capacity and long-life nonaqueous redox flow batteries

Organic molecules are promising active materials for nonaqueous redox-flow batteries (RFBs), but suffer from poor cycling stability. Here, the authors introduce azobenzene-based molecules as new type of highly soluble and stable active materials to realize high-capacity and long-life nonaqueous RFBs

Optimized Electrolyte with High Electrochemical Stability and Oxygen Solubility for Lithium-Oxygen and Lithium-Air Batteries

Lithium-oxygen (Li-O-2) batteries with high reversibility require a stable electrolyte against the side reactions with Li-metal anode and reactive oxygen species. Moreover, an electrolyte that can effectively utilize the low partial pressure of oxygen in the atmosphere has significant effect on the practical application of Li-air batteries. In this study, a localized high-concentration electrolyte (LHCE) was developed using 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE) as a diluent, which satisfies all these conditions simultaneously. The OTE-based LHCE exhibits much improved electrochemical performance in Li-O-2 batteries and Li-air batteries in comparison to the conventional electrolyte and high-concentration electrolyte. The design principles of this electrolyte also provide important guidelines for research to further develop new electrolytes for Li-O-2 and Li-air batteries

Effects of Fluorinated Diluents in Localized High‐Concentration Electrolytes for Lithium–Oxygen Batteries

A stable electrolyte is critical for practical application of lithium-oxygen batteries (LOBs). Although the ionic conductivity and electrochemical stability of the electrolytes have been extensively investigated before, their oxygen solubility, viscosity, volatility, and the stability against singlet oxygen (O-1(2)) still need to be comprehensively investigated to provide a full picture of the electrolytes, especially for an open system such as LOBs. Herein, a systematic investigation is reported on the localized high-concentration electrolytes (LHCEs) using different fluorinated diluents in comparison with those of conventional electrolytes. The physical properties and activation energies for reactions with singlet oxygen (O-1(2)) of these electrolytes are calculated by density functional theory. The electrochemical performances of LOBs using these electrolytes are compared. This study reveals that the correlation between the stability of the electrolytes and their physical and electrochemical properties depends strongly on the diluents in LHCEs. Therefore, it shines light on the rational design of new electrolytes for LOBs