Date of Thesis
Spring 2024
Description
Energy storage in the bonds of common chemical feedstocks is an attractive solution to the unreliability of wind and solar power due to its long term efficiency and easy recoverability. Energy is stored by reducing chemicals like ammonia, formic acid, and hydrogen, the reaction of which is dependent on a catalyst. To catalyze the reaction, the catalyst undergoes a slow proton transfer (PT) step to form what is known as a metal hydride. The sluggish kinetics of this step lower the effectiveness of the catalyst, and therefore must be better understood in order to improve the efficiency of energy storage processes in chemical feedstocks. This study aims to better understand the rate of proton transfer for metal hydrides by examining the reorganization energy of five target complexes. The five complexes, short named [CoPy3]+, [CoPy4]+, [CoPy5]+, [TpMo(CO)3]⁻, and [Tp’Mo(CO)3]⁻, are computationally modeled using the Gaussian 16 program and analyzed to determine the extent of structural and solvent reorganization they each exhibit upon protonation. The reorganization energy, or energy required for the complexes and the solvent molecules surrounding them to rearrange upon protonation, was calculated for each target complex. A lower reorganization energy results in lower activation energy, and therefore faster kinetics. The findings are in good agreement with the initial expectations; the inner-sphere reorganization energy of [CoPy5]+ is minimal (2.46 kcal/mol), while those of [CoPy3]+ and [CoPy4]+ are large (19.80 and 26.13 kcal/mol, respectively). The inner-sphere reorganization energies for [TpMo(CO)3]⁻ and [Tp’Mo(CO)3]⁻ are larger than expected (18.20 and 18.45 kcal/mol, respectively). The outer-sphere reorganization energy calculations are still ongoing, though we predict that the trends in total reorganization energy will mirror those for inner-sphere reorganization energy. The conclusion made from these results is that a desirable structure for the fast formation of a metal hydride should include ligands that have little availability to rotate or move, i.e. are interconnected with one another, and that are not strong π-acceptors.
Keywords
Metal Hydrides, Proton Transfer, Kinetics, Reorganization Energy, Computational Chemistry, Density Functional Theory
Access Type
Honors Thesis
Degree Type
Bachelor of Science
Major
Chemistry
First Advisor
Yan Choi Lam
Second Advisor
Douglas Collins
Recommended Citation
Ford, Megan, "Computational Study of Proton Transfer at Transition Metal Hydrides" (2024). Honors Theses. 692.
https://digitalcommons.bucknell.edu/honors_theses/692