Dissertation
Investigation of novel C-donor ligands with unique properties and their applications in Suzuki coupling
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2024
DOI: 10.25820/etd.007678
Abstract
Ligand design has been at the forefront of numerous advances in chemistry, particularly in organometallic chemistry, homogeneous catalysis, and material science. While carbon atoms have been integral to organic synthesis, their use in coordination chemistry has been limited. The introduction of carbenes, especially N-heterocyclic carbenes, marked a turning point, bringing carbon ligands into focus. However, neutral carbon ligands other than N-heterocyclic carbenes have remained underdeveloped. Recently, ylides with highly electron-rich carbon donor atoms have been gaining attention for their metal-ligating properties. This thesis primarily focuses on evaluating the coordination properties of ylides and establishing them as alternative carbon-donor ligands.
Chapter 1 introduces the background and significance of ligand design in coordination chemistry, highlighting the importance of η¹ C-donor ligands and the emergence of ylides as potential candidates.
Chapter 2 details the synthesis and characterization of various η¹ C-donor ligands that combine 4-alkylidene dihydropyridines (ADHPs) stabilized by phosphonium ylides. The strategic positioning of the phosphonium group was found crucial for their easy synthesis and isolation under mild conditions. The ligating properties of these ligands has been established through the synthesis of various Pd(II) and Rh(I) complexes. The X-ray crystal structures of these complexes clearly depict carbon-metal single bond characteristics, validating the new ligand design as η¹ carbon donor ligands. The high electron density of these ligands was assessed through IR spectra by examining the CO stretching frequency of the Rh-CO complex, demonstrating the significant electron richness of the ADHP ligand framework.
Chapter 3 expands on the understanding of the newly designed ligands by introducing a sulfone functionality at the 4-picolyl position of the alkylidene dihydropyridine. These modified ligands also showed excellent C-ligating ability, resulting in the formation of various Pd(II) and Re (I) complexes. Their high electron density was further confirmed by the low CO stretching frequency of Re complexes incorporating these ligands.
Chapter 4 explores the application of the alkylidene dihydropyridine ligands by using the corresponding metal complexes as catalysts for Suzuki coupling. The first- and second-generation catalysts displayed moderate to good catalytic activity for a wide range of substrates under mild conditions. Preliminary results regarding their application as catalysts in cross-coupling reactions are indeed encouraging.
Additionally, preliminary tests were conducted to explore the potential of these ligand frameworks as precursors to more exotic neutral carbon ligands like carbones or yldiides, demonstrating the high tunability of the ADHP ligand frameworks developed during the study.
In conclusion, this study has developed a highly stable and interesting class of η¹ C-donor ligands. Their structural features have been well documented, and several complexes incorporating the newly designed alkylidene dihydropyridine framework have been synthesized and characterized. The application of these ligands in Suzuki coupling reactions underscores their potential as potent C-donor ligands with valuable properties for metal catalysis.
Details
- Title: Subtitle
- Investigation of novel C-donor ligands with unique properties and their applications in Suzuki coupling
- Creators
- Anushree Poddar
- Contributors
- F. Christopher Pigge (Advisor)Dave Martin (Committee Member)Florence J. Williams (Committee Member)Louis Messerle (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Summer 2024
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.007678
- Number of pages
- xvii, 278 pages
- Copyright
- Copyright 2024 Anushree Poddar
- Language
- English
- Date submitted
- 07/22/2024
- Description illustrations
- Illustrations, tables, graphs, charts
- Description bibliographic
- Includes bibliographical references (pages 128-141).
- Public Abstract (ETD)
This thesis explores the development and application of innovative molecules, known as ligands, which play a crucial role in various fields of chemistry. Ligands are essential for stabilizing metals and enhancing their reactivity, making them vital in creating new materials and catalysts. Traditionally, carbon atoms have been central to organic chemistry but have been underutilized in binding to metals. The discovery of a special type of carbon-based ligand called carbenes marked a significant advancement, but other neutral carbon ligands have not been fully developed.
My research focuses on a promising class of carbon-based ligands called ylides, which have recently gained attention for their ability to bind strongly to metals. We designed and synthesized new ligands that combine specific carbon structures (4-alkylidene dihydropyridines, or ADHPs) with stabilizing groups (phosphonium ylides). These ligands were carefully analyzed to understand their structure and properties, and we found that their design allows for easy synthesis and stability under mild conditions.
We tested these new ligands by creating complexes with metals like palladium (Pd) and rhodium (Rh). These metal complexes were stable and showed clear carbon-metal bonds, confirming the effectiveness of our ligand design. Additionally, we assessed the electron-rich nature of these ligands, which is important for their binding ability, and found them to be highly effective.
To further enhance our ligands, we introduced a sulfone group, which improved their binding properties and resulted in stable palladium complexes. We also tested these ligands as catalysts for a chemical reaction known as Suzuki coupling, which is used to combine two molecules together. The new catalysts showed good performance under mild conditions, indicating their potential for practical applications.
In summary, this thesis presents the development of a new class of stable and versatile carbon-based ligands. These ligands have been thoroughly studied, and their potential in important chemical reactions has been demonstrated. Our findings open new possibilities for using carbon ligands in metal chemistry, paving the way for future advancements in the field.
- Academic Unit
- Chemistry
- Record Identifier
- 9984697845902771
Metrics
1 Record Views