Probing the Effects of Ligand Electronic Variation on the Hydrogen Atom Transfer Reactivity of the Copper(III)-Hydroxide Core

Abstract

Thermochemical and rate measurements were performed on copper(III)-hydroxide variants in order to understand the influence of the supporting ligand on the reactive nature of the copper(III)-hydroxide core ([CuOH]2+) in hydrogen atom transfer (HAT) reactions. The thermodynamic and kinetic behaviors of the [CuOH]2+ moiety in reactions with C-H containing substrates were shown to be sensitive to electronic modifications made to the supporting pyridine dicarboxamide ligand framework, as evaluated by electrochemical, pKa, and bond dissociation enthalpy (BDE) measurements, and through determination of second-order rate constants, activation parameters, and kinetic isotope effects (KIEs). Likewise, the analogous reactions with phenolic substrates were also shown to obey a similar correlation between reaction rate and thermodynamic driving force, even displaying a change in mechanism when the thermodynamics of HAT and proton transfer (PT) become similar. The results presented in this dissertation are explored within the broader scope of understanding both the macroscopic relationship between reaction rate and driving force for HAT reactions, as well as more nuanced aspects of these reactions such as proton tunneling, changes in mechanism, and the role of charge. Implications for ligand design elements are also drawn within the context of pyridine dicarboxamide supported copper(III) complexes, which may be generalizable to the design of transition metal complexes as a whole.