Developing and Understanding Catalysts for Organic Synthesis

Organic synthesis relies on improving catalyst designs and understanding reaction mechanisms for the advancement of the field. This dissertation will describe projects in both of these areas. First it will cover new photocatalysts in the aim of maintaining reactivity while increasing solubility in less polar solvents, and second understanding the importance of intermolecular interactions between new nucleophilic catalysts and substrates. Photocatalysis has become a major focus as a sustainable pathway for chemical reactions with visible light photocatalysts performing a large range of reactions such as redox reactions, cyclization reactions, and energy transfer reactions. Chapter 1 will discuss classes of organic photocatalysts commonly used in the field and the goals for developing future catalysts. Silicon phthalocyanines have been largely ignored as photocatalysts in photocatalytic reactions, despite their low energy excitation, long triplet lifetimes, and their ability to form singlet oxygen. In chapter 2, we will discuss three silicon phthalocyanine catalysts we developed for photocatalysis. Using cyclic voltammetry and Stern Volmer quenching studies, we have shown silicon phthalocyanines can act as electron donors or acceptors with appropriate substrates. We have successfully used silicon phthalocyanines in a reductive quenching reaction and in energy transfer reactions utilizing singlet oxygen as a reactant. These reactions, as well as the photophysical and electrochemical experiments will be discussed. In asymmetric catalysis, intra- and intermolecular interactions can be important for influencing catalyst/substrate arrangements to obtain selective reactions. Cation-pi interactions are one such interaction, that is frequently suggested to aid in reaction control. Isothiourea catalysts are nucleophilic catalysts that tend to form a cationic intermediate during the reaction and are hypothesized to participate in cation-pi interactions. Chapter 3 will directly focus on the cation-pi interaction we believe is occurring during an alcohol silylation reaction by analyzing electron rich and electron poor nonchiral isothiourea catalysts to understand how changes in the catalyst affect interactions with substrates. Competition studies with electron-rich and electron-poor substrates are used as a tool to probe this interaction and the results obtained will be discussed