Browsing by Subject "Hydrogen Atom Transfer"
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Item Probing the Effects of Ligand Electronic Variation on the Hydrogen Atom Transfer Reactivity of the Copper(III)-Hydroxide Core(2016-11) Yee, GereonThermochemical 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.Item Properties and Hydrogen Atom Transfer Reactivity of Copper(III)-Hydroxide Complexes(2018-01) Dhar, DebanjanThe conversion of C-H bonds in hydrocarbons to C-O bonds is one of the grand challenges in chemistry as it involves the energy demanding preliminary step of removing a hydrogen atom from the strong C-H bond via an initial hydrogen atom transfer step. A number of high-valent reactive transition metal-oxygen species are proposed to be the key intermediates that perform such hydrogen atom transfer reactions in biological and synthetic systems. The mononuclear copper(III)-hydroxide unit has been demonstrated to be a potent reactive species in this regard. The work in this thesis is focused on the chemistry of such synthetic mononuclear copper(III)-hydroxide cores generated using strongly electron donating pyridine di-carboxamido based ligand scaffolds. In particular the spectroscopic properties and hydrogen atom transfer reactivity of a series of such copper(III)-hydroxide complexes is explored in the light of the well established proton-coupled-electron transfer theory. The effects of ligand electronic perturbations on the properties and reactivity patterns of these compounds is explored through detailed spectroscopic and mechanistic invetsigations, with the ultimate aim of elucidating the intrinsic factors that contribute to the high efficiency of such species as hydrogen atom transfer reagents. A key conclusion from all of these studies is that the thermodynamic driving force plays a crucial role in determining the rates and mechanism of such hydrogen atom transfer reactions, and that a systematic tuning of the supporting ligand electronics modulates these intrinsic thermodynamic driving forces.