UC Irvine

This dissertation examines two forms of redox-controlled reactivity. First, bio-inspired organic carriers for carbon capture are examined (Chapters 1–3). Second, studies of alkene conversion methods using cobalt catalysis are described (Chapters 4–6).Chapter 1 traces quinone and flavin chemistry from their biological roles as membrane and cofactor electron carriers to synthetic redox carriers for electrochemical carbon capture, and develops the thermodynamic framework that connects reduction potential, hydrogen bonding, and CO₂ or proton affinity. Chapter 2 applies this framework to hydroxymethylated benzoquinones (HMQ A–D), designed so that a flexible proximal hydroxymethyl group can hydrogen-bond to the reduced quinone without blocking the site of CO₂ attack. In the MQ → MMQ → HMQ A control series, computed reduction free energies separate the inductive contribution of the ether oxygen from the hydrogen-bonding contribution of the hydroxymethyl donor. The inductive increment is nearly identical for both reductions, whereas the hydrogenbonding increment more than doubles at the dianion. Crystallography shows the donor engaged intermolecularly in the neutral solid, while conformer calculations show that folded, intramolecularly hydrogen-bonded dianions may dominate in solution. ¹H and ¹³C NMR spectroscopy identify an aryl-carbonate CO₂ adduct, and Benesi–Hildebrand analysis of spectrophotometric titrations gives log KCO2 = 3.34 for HMQ A. Chlorination shifts the reductions anodically by up to 250 mV while CO₂ binding remains substantial (log KCO2 = 3.1– 3.3 for HMQ B–D), and TD-DFT calculations assign the spectra of the oxidized, dianion, and CO₂-bound states, connecting the redox shifts to stabilization of the redox-active π* orbital. Positioned hydrogen-bond donors and electron-withdrawing substituents together are observed to mitigate the trade-off between reduction potential and CO₂ affinity that constrains quinone-based capture.Chapter 3 extends the design question to water with flavin derivatives, where the design relies on proton transfer, not on direct CO₂ binding. Three water-soluble N10-aryl flavins bearing anionic (Fl-1) or cationic (Fl-2, Fl-3) side chains were characterized across five oxidation and protonation states by voltammetry, Pourbaix analysis, spectroelectrochemistry, pulse radiolysis, and TD-DFT. In buffered pH 7 electrolyte the two-electron potentials of all three fall within 10 mV, showing that a remote solvated charge is a weak handle on flavin potential, while the pendant hydroxyl of Fl-3 lowers the hydroquinone pKₐ from ~7.1 to 6.4 and thereby sets the proton-uptake window. Pulse radiolysis resolved the neutral and anionic semiquinone spectra that electrolysis cannot accumulate. Bulk electrolysis of Fl-2 and Fl-3 in CO₂-containing electrolyte raised the solution pH by 2.1 units for Fl-2 and 3.5 units for Fl-3, and headspace CO₂ fell on reduction and recovered on reoxidation. At 63–80 mM solubility, and with the release half of the cycle not quantified, Fl-2 and Fl-3 serve as mechanistic probes, not as candidate mediators.Chapters 4–6 turn to cobalt-hydride-mediated alkene chemistry, where oxidation-state control directs carbon-centered reactivity. Chapter 4 reviews metal-hydride hydrogen-atom transfer (MHAT) and oxidative radical–polar crossover, the sequence that converts an alkene into a carbocation equivalent under mild conditions. Chapter 5 describes cobalt(II)-salencatalyzed hydroazolation and Markovnikov hydration of alkenes; H₂¹⁸O labeling studies established water as the dominant oxygen source in THF, and the survey of catalysts and substrates located the central limitation in substrate-dependent stereocontrol of intermolecular capture, not in water incorporation. Chapter 6 develops a cobalt-catalyzed oxidative Grob fragmentation that converts cyclic homoallylic alcohols into acyclic alkene-containing ketones without a pre-installed leaving group, in ¹H NMR yields up to 73%. Component controls, an intact cyclopropyl radical clock, and the water-suppressed side chemistry of a dioxolane substrate support a shared cationic pathway after oxidation, with a second MHAT at the product alkene as the principal competing pathway.Across both halves of this dissertation, the redox state of a molecule, set electrochemically at an electrode or chemically by a catalyst, is the control element that turns weak, reversible interactions into selective bond formation, whether the electrophile is CO₂ approaching a quinone dianion or a carbocation completing a fragmentation.