Publication in: Fall 2022 Issue

Dihydrogen Heterolysis and Hydride Transfer utilizing an Iridium Catalyst
Olive Solares-Knorr
Faculty Mentor(s):
Meghan McGreal
Abstract / Summary:
Hydride transfer is an efficient means of reducing oxidized matter for a variety of purposes, and iridium is a popular metal center when homogeneous methods are used. Hydrogen gas is the most used method of obtaining a hydride. The goal of this study is to computationally analyze an iridium catalyst’s potential to obtain and transfer a hydride. In particular, an Iridium (III) catalyst containing a picolinamide bidentate ligand as well as a cyclopentadienyl half sandwich. In aqueous solution the catalyst can reduce carbon dioxide to formic acid. Energy and geometry calculations of a published study utilize the density functional theory method m06, and however this study will process the data differently, use the basis set cc-pvdz for all atoms except iridium which will utilize LANL2DZ’s effective core potential, and the solvent model will utilize a different permittivity. The data is qualitatively similar, with the largest deviation likely caused by the values of the relative permittivity, of which this study does not acknowledge the ionic strength of the solution. Nonetheless, the data was used to compare point modifications on the catalysts picolinamide ligand to the molecular geometry and energetics of the chemical environment. From these energy and geometry calculations the catalytic efficiency and dynamics of the catalyst can be inferred. It was found that the point modifications decrease catalytic efficiency probably because they disrupt the conjugation and e- inductive effects. The vinyl functional group maintains the symmetry of the p orbitals however the lack of an oxygen causes its energy to increase relative to the control, but this intermediate is still downhill from the subsequent step. We can infer that means maintaining the resonance stability of the picolinamide is more important for the structure of the intermediate than just the presence of the strongly electronegative oxygen. The second pattern is found in the optimizations after [Ir-H2O] where the catalyst has a greater number of σ-bonds. While the Ir has more electron density around it the hydroxyl point modification is lower in energy than the vinyl, but only slightly (<2 kcal/mol).
Publication Date: