UC Irvine

Reversible catalysis is a hallmark of energy-efficient chemical transformations, but can only be achieved if the changes in free energy of intermediate steps are minimized and the catalytic cycle is devoid of high transition-state barriers. In Chapter 1, using these criteria, we demonstrate reversible CO2 to HCO2– conversion catalyzed by [HPt(depe)2]+ (where depe=1,2-bis(diethylphosphino) ethane). Direct measurement of the free energies associated with each catalytic step correctly predicts a slight bias towards CO2 reduction. We demonstrate how the experimentally measured free energy of each step directly contributes to the <50 mV overpotential. We also find that for CO2 reduction, H2 evolution is negligible and the Faradaic efficiency for HCO2– production is nearly quantitative. A free-energy analysis reveals H2 evolution is endergonic, providing a thermodynamic basis for highly selective CO2 reduction.

In Chapter 2, the kinetics of each step of the catalytic cycle for CO2 reduction is assessed as a means to elucidate the nature of the sluggish catalytic rate. By measuring the rates of electron transfer, protonation, and CO2 insertion, it was shown that the catalytic rate is limited by CO2 insertion into [HPt(depe)2]+.

Chapter 3 diverges from the common themes discussed in this dissertation and describes the role of lithium chloride for enabling the insertion of metallic zinc into organic halides. The sensitivity provided by fluorescence microscopy enabled the observation of surface intermediates in the synthesis of soluble organozinc reagents by direct insertion of alkyl iodides to commercial zinc powder. Five hypotheses were examined for the mechanistic role of lithium chloride in enabling this direct insertion. The data are consistent with lithium chloride solubilizing organozinc reagents from the surface of the zinc after oxidative addition.