Citation
He, Tianyi (2025) Synthesis and Spectroscopy of Open-Shell Complexes Bearing Unusual M-E (E = N, C) Bonding Motifs and Synthesis of Novel Weakly-Coordinating Anions with Applications in Coordination Chemistry and Electrochemistry. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/27c4-ey05. https://resolver.caltech.edu/CaltechTHESIS:05292025-183641323
Abstract
This dissertation focuses on a diverse range of topics centered around inorganic synthesis, ranging from spectroscopic studies of rare bonding motifs (Chapter 3 and Chapter 4) and applications of novel weakly-coordinating anions in applications in coordination chemistry and electrochemistry (Chapter 1 and Chapter 2). While the projects described herein are distinct in the nature of their execution, the utility and applications of synthetic inorganic chemistry are highlighted in all of the projects. Chapter 1 describes the design principles and the synthesis a novel weakly-coordinating anion based on alkyl or aryl substituted silicates bearing fluorinated pinacolate ligands. A wide range of anions bearing distinct R groups were prepared, enabling facile tuning of anion sterics and solubility. A range of cations invoked in chemical reactivity studies supported by these novel anions was prepared, highlighting the utility of these novel anions in both coordination and catalysis. Cations relevant to electrochemical studies were also accessed, wherein the exceptionally wide stability window for the methyl-substituted variant was demonstrated. Reversible magnesium deposition and stripping supported by these anions were also shown, demonstrating the utility of these novel anions in next-generation battery chemistry applications. Chapter 2 describes efforts towards developing reproducible and stable magnesium deposition and stripping chemistry supported by a novel silicon-based weakly-coordinating anion. Aspects that impact reproducible and stable magnesium electrochemistry described in prior literature were studied in detail. Emphasis was placed on probing the prevalent hypothesis in magnesium electrolyte literature that magnesium alkyl, aryl, and amido additives improve electrochemical performance by acting as water or impurity scavengers. A range of magnesium additives were tested, wherein the identity of the additives was shown to dictate magnesium deposition and stripping behavior. An unconventional magnesium hydrocarbyl species was identified as the active species responsible for improved Mg deposition/stripping performance, highlighting the utility of synthetic inorganic chemistry in elucidating fundamental electrochemistry. Chapter 3 describes the synthesis and the spectroscopy of an unusual molybdenum para-terphenyl diphosphine complex bearing a terminal nitride and a parent amide motif. Detailed continuous wave- and pulse-electron paramagnetic resonance techniques were employed the interrogate the electronic structure of this unusual open-shell motif, revealing significant radical character on the amide motif. On the other hand, the terminal nitride motif showed negligible spin density. With further insight obtained from density functional theory calculations, the high spin density on the terminal amide motif was attributed to significant orbital overlap between the amide nitrogen py orbital with the Mo dxy orbital. Chapter 4 describes the synthetic, spectroscopic, and computational studies of a pentametallic molybdenum-iron-sulfur cluster of MoS3Fe3CMo composition with μ4-carbide and μ2-CO motifs that resembles the lo-CO form of nitrogenase. The cluster was accessed via carbide transfer from a Mo carbide complex supported by a para-terphenyl diphosphine ligand. Different isotopologues of this cluster were accessed by selectively labelling the molybdenum para-terphenyl diphosphine precursor. This cluster displays an S = ½ ground spin state amenable for pulse electron paramagnetic resonance spectroscopy. Detailed spectroscopic studies reveal a significantly larger carbide hyperfine interaction than any observed for various states of nitrogenase studied thus far, thereby providing benchmarking information for metal-carbon interactions studied by electron paramagnetic resonance methods. Appendix A describes the synthesis and preliminary reactivity studies of a heterometallic molybdenum-iron-nickel cubane supported by a bulky bisphenoxide ligand with a central anthracene linker, relevant to the active site of the nickel-iron carbon monoxide dehydrogenase. Preliminary electron paramagnetic resonance studies on this cubane were suggestive of an S = 2 ground state, wherein incorporation of a formal closed-shell nickel site into a trimetallic cluster significantly perturbs the electronic structure. Appendix B describes efforts towards accessing molybdenum para-terphenyl disphosphine carbyne complexes with no bound carbon monoxide ligands. Preliminary studies on the molybdenum carbyne complexes showed that molybdenum complexes with a terminal carbide and a terminal chloride can be accessed. Appendix C describes the synthesis and preliminary electrochemical studies of novel dianonic silicates supported by fluorinated pinacolate ligands, wherein magnesium deposition and stripping supported by a novel dianion was demonstrated.
| Item Type: | Thesis (Dissertation (Ph.D.)) | |||||||||
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| Subject Keywords: | Weakly-coordinating anions, electrochemistry, next-generation batteries, Mg electrolytes, non-innocent ligands, electron paramagnetic resonance, molybdenum, Fe-S clusters, carbide, Nitrogenase, [NiFe]-CODH | |||||||||
| Degree Grantor: | California Institute of Technology | |||||||||
| Division: | Chemistry and Chemical Engineering | |||||||||
| Major Option: | Chemistry | |||||||||
| Thesis Availability: | Not set | |||||||||
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| Defense Date: | 14 May 2025 | |||||||||
| Record Number: | CaltechTHESIS:05292025-183641323 | |||||||||
| Persistent URL: | https://resolver.caltech.edu/CaltechTHESIS:05292025-183641323 | |||||||||
| DOI: | 10.7907/27c4-ey05 | |||||||||
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| Default Usage Policy: | No commercial reproduction, distribution, display or performance rights in this work are provided. | |||||||||
| ID Code: | 17298 | |||||||||
| Collection: | CaltechTHESIS | |||||||||
| Deposited By: | Tianyi He | |||||||||
| Deposited On: | 30 May 2025 23:30 | |||||||||
| Last Modified: | 30 May 2025 23:30 |
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