|
Document Type |
: |
Thesis |
|
Document Title |
: |
Computational Study of the Processes Relevant to Hydrocarbon Metathesis Pathways Catalyzed by Homo and Heterogeneous Catalysts دراسة نظرية لتحفيز العمليات المرتبطة بتغير مسار تفاعلات الهيدروكربونات بواسطة محفزات متجانسة وغير متجانسة |
|
Subject |
: |
Faculty of Science |
|
Document Language |
: |
Arabic |
|
Abstract |
: |
Homogeneous and Heterogeneous catalysts remain to be the most useful complexes used in the catalysis of metathesis processes for the synthesis of new carbon-carbon sigma or double bonds. The investigation of the influence of changing the Ligand environment on the catalytic performance has led to important improvements in the field. Furthermore, Theoretical chemistry can be used to speed up the design of new catalysts with improved properties by providing a complementary approach for understanding catalysis mechanisms. To this extent, Density Functional Theory (DFT) calculations have significantly contributed by providing fundamental understandings for the development of new catalysts. With this aim, we presented in this thesis a detailed computational study of how the nature of the ligands binding to the metal affects the global properties and reactivity of the catalyst. Geometric, energetic, and electronic analyses were carried out in order to obtain the key insights required to construct structure-performance correlations.
The use of Hoveyda-Grubbs-type complexes with different anionic ligands were studied computationally to promote the initiation reaction for ethene metathesis. Although the activation step can occur via the Associative, Dissociative, or Interchange mechanisms, our energetic calculations indicate that the dissociative route is the most plausible one for the ethene metathesis reaction. In addition, the effect of replacing the chloride anionic ligands in analogous catalysts with different ligands having variable electrodonicity scales were investigated in this study. The results revealed that the pre-catalysts carrying strong electron withdrawing ligands, such as triflouromethyl CF3 or nitrile CN ligands, afforded the most reactive and the lowest energy needed for catalyzing the activation reaction.
Furthermore, silica supported tungsten carbyne and tungsten hydride complexes were investigated regarding their activation mechanism in cyclic alkane metathesis. Both tungstocarbynes and tungstohydride catalysts demonstrated comparable reactivity in the production of the active species tungstocarbene-hydride. However, when considering the catalytic cycle for the cycloalkane metathesis, the formation of the propagating tungstocarbene-hydride proceeds via -H transfer pathway for tungstohydrides versus the less energy barrier -H transfer pathway in the case of tungstocarbyne complexes. On the other hand, the electronic analysis suggested that the tungstohydride catalyst was more reactive due to the favored electron deficiency of tungsten metal atom with a higher electrophilicity and stability, which assisted the nucleophilic attack from the cycloalkane substrate.
This study is expected to provide a conceptual framework for future catalyst development efforts and to aid practitioners in selecting a specific catalyst for a given application. Furthermore, in the long term, research like this will help in the prediction of new catalyst properties through computation. |
|
Supervisor |
: |
Prof. Dr. Osman Abdelkarim |
|
Thesis Type |
: |
Doctorate Thesis |
|
Publishing Year |
: |
1444 AH
2022 AD |
|
Co-Supervisor |
: |
Prof. Dr. Shaaban A. Elroby |
|
Added Date |
: |
Tuesday, February 28, 2023 |
|
Researchers
| منى عبيد البلوي | Albalawi, Mona Obead | Researcher | Doctorate | |
|