Interrogating the Influence of Electronics and Solvation on Thermodynamic Hydricity

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  • March 19, 2019
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  • Brereton, Kelsey
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • A ‘hydrogen economy’ using dihydrogen (H2) as a fuel has been proposed as a leading strategy for new environmentally friendly energy sources. Toward this end, the safe and efficient storage of H2 is an ongoing challenge in successful implementation on an industrial scale. As key catalysts in hydrogenation and hydrogen production reactions, transition metal hydride complexes must balance the strength of the metal hydride bond to maximize reactivity and retain stability. This work focuses on an in-depth investigation into the intricate thermodynamics that govern these systems and their potential use in guiding catalyst design and optimizing performance. The hydricity of metal hydride complexes is a thermodynamic measure of the strength of the metal hydride bond. Hydricity has been measured extensively in acetonitrile and has been used as a valuable tool to guide catalyst design. The utility of these thermodynamic measurements has motivated expanded studies investigating the observed solvent dependence of hydricity. Presented here are three focused studies examining strategies for measurement, solvent dependence, and catalytic utility of hydricity. 1) A bimetallic Ir/Ru catalyst is used as a case study of solvent dependent thermodynamics. The electrochemistry, acidity, hydricity, and electronic structure of the complex is explored in two solvents and applied to a detailed picture describing catalysis observed by the system. 2) Density Functional Theory (DFT) calculations are used to overcome traditional challenges in aqueous hydricity measurement. Through the development of appropriate training sets to calibrate computational results, the reduction potentials and acidities of a series of iridium complexes are determined in water and used to calculate aqueous hydricities for comparison with experimental values. 3) The first example of a systematic study of the solvent dependence of hydricity across a series of electronically tuned iridium catalysts is presented in acetonitrile and water: this work explores the connection between the influence of electronic tuning and effective hydricity. This work unveils the thermodynamics driving kinetic observations for transition metal hydride complexes. Through a thorough understanding of the optimal strategies for catalyst tuning in multiple solvents, new generation of systems powering the ‘hydrogen economy’ can be developed.
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Advisor
  • Miller, Alexander
  • Meyer, Gerald
  • Dempsey, Jillian
  • Leibfarth, Frank
  • Waters, Marcey
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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