The selective activation and functionalization of C–H bonds is a major challenge in synthetic chemistry. Transition metal-oxo complexes are particularly adept at accomplishing such transformations. This has motived many studies into what factors control and predict the concerted proton electron transfer (CPET) reactivity between transition metal-oxo complexes and C–H bonds. Recently, there has been a much interest in, and no little controversy over, whether and how such C–H activation is influenced by the stepwise free energies of proton transfer and electron transfer, ΔG°PT and ΔG°ET. At the time this research commenced, there was no clear framework for how these free energies affect CPET in general nor an understanding of whether their effect is distinct from their contribution to the overall driving force of the reaction ΔG°CPET.This dissertation begins in Chapter 2 with the broadest study of transition metal-oxo mediated C–H activation to date. Reported rates of reactivity between transition metal-oxo complexes and DHA are found to only be predicted by the stepwise thermodynamic parameters ΔG°CPET, ΔG°PT, and ΔG°ET. Long-held beliefs regarding the reactivity of transition metal-oxo complexes towards C–H bonds, most notably the importance of high spin states, are not predictive of reaction rates. Our analysis demonstrates that ΔG°PT and ΔG°ET have an influence on reaction rates independent of their contribution to ΔG°CPET, and that this influence is not easily explained as a textbook linear free energy relationship. Despite the mounting evidence for the role of stepwise thermodynamics in CPET reactions, there has been controversy over whether their effect is compatible with proton tunneling. Chapter 3 addresses this controversy by investigating the role of quantum tunneling in the ΔG°PT-dependent CPET reactions between a cobalt(III)-oxo complex and C–H bonds. Variable temperature kinetic isotope effects support extensive proton tunneling in this reaction. Chapter 4 presents a computational study which demonstrates how this tunneling is enhanced by a lower ΔG°PT. There is a link between the C–H bond acidity, the anharmonicity of the proton potential energy well, and the overall rate of the reaction. This means that structure-reactivity relationships can be invoked even with a quantum mechanical treatment of protons. Model calculations parameterized with these computations demonstrate that experimentally observed trends with ΔG°PT and ΔG°ET can be explained primarily through the influence of stepwise thermodynamic on the proton potential energy wells. Extending these studies of thermodynamic effects on C–H activation to strong C–H bonds required developing a new strategy for stabilizing highly reactive transition metal-oxo species capable of activating such bonds. Chapter 5 presents the development of a new ligand scaffold which is resistant to oxidation and preliminary studies on using this scaffold to generate high-valent transition metal-oxo complexes. The combination of a mesoionic scorpionate scaffold with trifluoromethyl groups yields a ligand which similar electron properties to established tris(imidazol-2-ylidene)borate scorpionate ligands, but with oxidatively robust trifluoromethyl flanking groups. This ligand supports the first ever isolation of a stable dicobalt(IV) complex, demonstrating the ability of this ligand to stabilize highly reactive species.