Computational techniques, mostly density functional theory (DFT), were applied to study metal-based catalytic processes for energy conversion reactions. In the first and second projects, the main focus was on activation of the light alkanes such as methane, which have thermodynamically strong and kinetically inert C–H bonds plus very low acidity/basicity. Two Mo-oxo complexes with the different redox non-innocent supporting ligands, diamide-diimine and ethylene-dithiolate, were modeled. These Mo-oxo complexes are modeled inspired by active species of a metalloenzyme, ethylbenzene dehydrogenase (EBDH). The results for the activation of the benzylic C–H bond of a series of substituted toluenes by modeled Mo-oxo complexes show there is a substantial protic character in the transition state which was further supported by the preference for [2+2] addition over HAA for most complexes. Hence, it was hypothesized that C–H activation by these EBDH mimics is controlled more by the pKa than by the bond dissociation free energy of the C–H bond being activated. The results suggest, therefore, promising pathways for designing more efficient and selective catalysts for hydrocarbon oxidation based on EBDH active site mimics. Also, it is found that the impact of supporting ligand and Brønsted/Lowry acid/base conjugate is significant on the free energy barrier of C–H bond activation.
In the third project the focus was on assessing the nature of hydrogen in the transition state related to the transfer of hydrogen between a carbon and nitrogen in an experimentally studied hydroaminoalkylation process by a five-coordinate Ta complex. It was revealed that, for the studied substituents, pKa is a larger driving force in the rate-determining hydrogen transfer reaction than the BDFE, which suggest a reasonable amount of protic character in the transition state, and possible routes to the design of more active catalysts with greater substrate scope.
Finally, for the last project, the focus was on hydrotris(1,2,4-triazol-1-yl)borate complex as an electrocatalyst and study the impact of metal identity down a group or across a period of the d-block on proton-coupled electron transfer (PCET), which is a key process in many electrocatalytic cycles. The studied thermodynamics and kinetics trends for a series of mid to late 3d- and 4d-transition metals show the metal and its electronic structure greatly impact the nature of the PCET processes.
| Identifer | oai:union.ndltd.org:unt.edu/info:ark/67531/metadc1703312 |
| Date | 05 1900 |
| Creators | Nazemi, Azadeh |
| Contributors | Cundari, Thomas, Wang, Hong, Slaughter, LeGrande M., Cisneros, Andres, Surendranath, Yogesh |
| Publisher | University of North Texas |
| Source Sets | University of North Texas |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Format | xv, 111 pages, Text |
| Rights | Public, Nazemi, Azadeh, Copyright, Copyright is held by the author, unless otherwise noted. All rights Reserved. |
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