Computational Studies of Molecular-Level Effects at Catalytic Interfaces
Date of Award
Fall 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Batista, Victor
Abstract
The development of improved catalysts is essential to addressing contemporary challenges in alternative energy and chemical synthesis. In many cases, heterogeneous catalysts are preferred due to their stability and the ease of product separation. Alternatively, molecular catalysts can be attached to solid surfaces to combine the benefits of heterogeneous catalysts with the selectivity and tunability of transition metal complexes. In both heterogeneous and heterogenized catalytic systems, processes at the interface play a critical role in controlling activity and selectivity. Computational techniques allow for the study of catalytic interfaces at the molecular level, providing fundamental understanding of these interfacial effects. The reactivity of surface-attached catalysts can be modulated in situ by interfacial electric fields, which shift the electron density of reaction intermediates and transition states to alter the thermodynamics and kinetics of catalytic reactions. Chapter 2 discusses the effect of applied electric fields on the hydride transfer reactivity (hydricity) of iridium(III) half-sandwich complexes adsorbed on gold electrodes. It is shown that electric fields precisely and linearly control the aqueous hydricities of these catalysts without any chemical modification. These hydricity shifts are compared directly to those induced by ligand substitution, and are found to be equivalent to a dramatic change in substituent Hammett parameter. These findings will aid the design of catalytic systems that can be non-faradaically controlled by applied electric fields. In Chapter 3, the inductive effect of electric fields on the metal center of surface-attached complexes is investigated and quantified. Fundamental insights into the magnitude of these effects is essential to understanding the underlying mechanism of field control of catalytic reactions. Using a series of Group 6 metal complexes, it is shown that electric fields have a significant effect on the electron density at catalytic centers. A protocol for spectroscopically quantifying the inductive effect of fields is introduced based on monitoring the Stark shifts of vibrations that are perpendicular to the applied field. It is found that the design of the molecular linker between the catalytic center and electrode regulates the magnitude of the inductive effect, while the identity of the metal center plays a minor role. Direct comparison with vibrational shifts caused by chemical substitution provides an interpretable point of reference for the strength of the inductive effect. In Chapter 4, the structure of the catalytic interfaces is shown to regulate the selectivity of heterogeneous transfer hydrogenation reactions from tertiary amines to alkynes. The amine H donor forms a surface complex on Pt and Pd catalysts, creating isolated active sites for the hydrogen transfer reactions. At sufficient surface coverage, the amine stabilizes the cis alkene isomer through electronic interactions, allowing for selective transfer hydrogenation without the need for special synthetic techniques or additional surface modifiers. These mechanistic insights may provide a pathway for the design of improved heterogenous transfer hydrogenation systems where the H donor molecule is modified to create active sites that enhance reaction selectivity.
Recommended Citation
Kelly, H. Ray, "Computational Studies of Molecular-Level Effects at Catalytic Interfaces" (2023). Yale Graduate School of Arts and Sciences Dissertations. 1247.
https://elischolar.library.yale.edu/gsas_dissertations/1247
