Reaction of Hydrazones with Potassium Organotrifluoroborates Through Photoredox Catalysis
Session Title
Poster Session 1
Faculty Mentor
James Hanna, Ph.D.| Robin Lammi, Ph.D.| Aaron Hartel, Ph.D.
College
College of Arts and Sciences
Department
Chemistry, Physics, Geology, & the Environment
Abstract
Small molecules such as α-aryl amines and hydrazines, are important pharmaceutical building blocks. The synthesis of these types of molecules requires the formation of carbon-nitrogen bonds, significant because of their abundance in natural products, medicines, and biologically active molecules. Many approaches toward synthesizing these types of molecules have employed transition metals to catalyze the essential C-N bond formations. Previous studies in our group have focused on visible light photoredox-mediated alkylation of imines with potassium organotrifluoroborates (R-BF3K), using both transition-metal complexes and organic dyes. Using similar principles, this research is focused on the alkylation of hydrazones using R-BF3K. The reaction of benzaldehyde benzoylhydrazone and cyclohexyl-BF3K will be used to test various reaction conditions, such as photocatalyst, Lewis acid, and solvent. Using this model reaction, organic catalysts, such as Mes-Acr-Me, and transition-metal photocatalysts, such as Ir(dFCF3)dtb, were screened, and it was demonstrated that Ir-based complexes were highly effective (~98% conversion, determined by NMR). As compared to Ir-based complexes, Ru-based (~0% conversion) and organic (~70% conversion) photocatalysts were not as effective. The next steps will be to explore the scope and limitations and perform some mechanistic studies. The scope and limitations phase will use differently substituted hydrazones and organotrifluoroborates to explore various steric and electronic effects on the reaction. Stern-Volmer quenching studies will be used to verify the first step in the proposed mechanism, while light-dark experiments will help distinguish between a closed-cycle mechanism and a radical chain mechanism by analyzing product formation during periods of illumination.
Honors Thesis Committee
James Hanna, Ph.D., Robin Lammi, Ph.D., Aaron Hartel, Ph.D.
Course Assignment
CHEM 551/552H – Hurlbert
Previously Presented/Performed?
NC Photochem, Columbia, SC, October 2022 | SAEOPP McNair/SSS Scholars Research Conference, June, 2022 | Winthrop University Showcase of Winthrop University Undergraduate Research and Creative Endeavors, Rock Hill, SC, April 2023
Type of Presentation
Poster presentation
Grant Support?
Support was provided by the Donors of the American Chemical Society Petroleum Research Fund (# 58270-UR1), the Winthrop University McNair Scholars Program, and SC-INBRE from the National Institute for General Medical Sciences (P20GM103499).
Start Date
15-4-2023 12:00 PM
Reaction of Hydrazones with Potassium Organotrifluoroborates Through Photoredox Catalysis
Small molecules such as α-aryl amines and hydrazines, are important pharmaceutical building blocks. The synthesis of these types of molecules requires the formation of carbon-nitrogen bonds, significant because of their abundance in natural products, medicines, and biologically active molecules. Many approaches toward synthesizing these types of molecules have employed transition metals to catalyze the essential C-N bond formations. Previous studies in our group have focused on visible light photoredox-mediated alkylation of imines with potassium organotrifluoroborates (R-BF3K), using both transition-metal complexes and organic dyes. Using similar principles, this research is focused on the alkylation of hydrazones using R-BF3K. The reaction of benzaldehyde benzoylhydrazone and cyclohexyl-BF3K will be used to test various reaction conditions, such as photocatalyst, Lewis acid, and solvent. Using this model reaction, organic catalysts, such as Mes-Acr-Me, and transition-metal photocatalysts, such as Ir(dFCF3)dtb, were screened, and it was demonstrated that Ir-based complexes were highly effective (~98% conversion, determined by NMR). As compared to Ir-based complexes, Ru-based (~0% conversion) and organic (~70% conversion) photocatalysts were not as effective. The next steps will be to explore the scope and limitations and perform some mechanistic studies. The scope and limitations phase will use differently substituted hydrazones and organotrifluoroborates to explore various steric and electronic effects on the reaction. Stern-Volmer quenching studies will be used to verify the first step in the proposed mechanism, while light-dark experiments will help distinguish between a closed-cycle mechanism and a radical chain mechanism by analyzing product formation during periods of illumination.
