Experimental and Computational Analysis of Palladium-Mediated Cross Coupling. Part I: Palladium-Catalyzed Dehydrogenative Cross-Coupling of Alkylarenes with Carbon-Centered Nucleophiles. Part II: Blue Light Catalyzed Heck Reaction of Styrene Derivatives with Various C–I Bonds
Part I: Catalytic Dehydrogenative Cross-Coupling (CDC) is a valuable category of chemical reactions due to the eliminated need for prior functionalization and high overall atom economy. This work focuses on the experimental and computational studies performed while investigating the mechanism of a CDC with alkylarenes and carbon-centered nucleophiles. DFT calculations were carried out to determine the C–H activation pathway for the alkylarenes, and it was limited to two possibilities that preferentially activate the sp3 C–H bond over the sp2 C–H bond: Pd0-mediated oxidative addition or PdI-mediated concerted metalation deprotonation (CMD). Competition experiments were carried out with different alkylarenes to help differentiate the two potential routes, but the results were inconclusive. It was then discovered that the active catalyst is heterogeneous, which would complicate the previous calculations since those were modelling a solvated system. There are five types of substrates that undergo this unique chemistry, but there are eight that do not, so one of the goals was to determine what quantitative parameters could explain (and therefore predict) trends in reactivity. Calculated monomer and dimer bond dissociation energies (BDEs), radical nucleophilicity values, and ligand exchange energies were compared for all 13 substrates. Kinetic data on each step–monomer dimerization and dimer coupling with toluene–provided a quantitative explanation for substrate success. Successful dimerization is influenced by monomer C–H BDEs. Part II: Vladimir Gevorgyan reported a blue LED catalyzed Heck reaction between styrene derivatives and different alkyl and aryl iodides. This work focuses on the computational exploration of the role the blue light plays in this transformation. While a diabatic photoreaction was considered to explain the iodine atom abstraction, this theory was disproven by experimental UV/Vis spectra. A Jablonski diagram was constructed and showed that the Pd(PPh3)3 can be photoexcited by blue light to form the first triplet excited state, which can then abstract an iodine atom from the starting material.
Amadeo, Peter Anthony, "Experimental and Computational Analysis of Palladium-Mediated Cross Coupling. Part I: Palladium-Catalyzed Dehydrogenative Cross-Coupling of Alkylarenes with Carbon-Centered Nucleophiles. Part II: Blue Light Catalyzed Heck Reaction of Styrene Derivatives with Various C–I Bonds" (2019). Dissertations available from ProQuest. AAI27543783.