Author ORCID Identifier
Document Type
Thesis
Date of Award
Spring 4-24-2026
Keywords
Photoredox catalysis, Iridium, Dicyanobenzene, Allylic arylation, cyclohexene, methylcyclohexene, NMR
Degree Name
Chemistry (BA, BS)
Department
CHEMISTRY
First Advisor
Dr. John R. Swierk
Series
Science and Mathematics
Abstract
The mechanism of the photoredox-catalyzed allylic arylation of cyclohexene with 1,4- dicyanobenzene (DCB) using tris(2-phenylpyridine)iridium(III) and a thiol hydrogen atom transfer (HAT) co-catalyst has been the subject of ongoing mechanistic debate. Three competing pathways have been proposed: radical-radical coupling, radical addition, and fragment-radical-radical coupling. In this work, methyl-substituted cyclohexene derivatives are employed as mechanistic probes to interrogate product distributions and reaction efficiency using ¹H and 2D NMR spectroscopy and external quantum yield measurements. Quantum yields across all substrates remained below one, confirming significant loss to unproductive pathways and ruling out a chain mechanism. Among the derivatives, 1-methylcyclohexene was found to be the most reactive substrate despite computational predictions that the proposed radical-radical coupling mechanism would render it minimally reactive during the hydrogen atom transfer step. Product distributions across all three methylated derivatives were consistent internally, retained the same selectivity factors in direct competition within the 3-methylcyclohexene reaction, and cannot be explained by either the radical coupling or radical addition mechanisms. These findings are most consistent with a fragment-radical-radical coupling pathway in which the DCB radical anion undergoes irreversible cyanide loss to form a benzonitrile radical prior to coupling with the HAT-generated allylic radical. Product selectivity is governed by the relative stability and steric accessibility of the allylic radical intermediates. This work demonstrates the efficacy of strategic substrate selection as a mechanistic probe and motivates further investigation into solvent participation, radical stability, and kinetics in photoredox catalysis.
Recommended Citation
Payne, Michael J., "STRATEGIC SUBSTRATE MODIFICATION AS A MECHANISTIC PROBE IN PHOTOREDOX CATALYSIS: AN NMR AND QUANTUM YIELD STUDY" (2026). Undergraduate Honors Theses. 61.
https://orb.binghamton.edu/undergrad_honors_theses/61
