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Abstract
This thesis explores the coordination chemistry of functionalized thiourea ligands with electron-withdrawing sulfonyl, phosphoryl and diacyl substituents. These ligands, despite their structural similarity to acylthioureas, exhibit unique coordination behaviours that have been largely understudied within the literature, particularly with platinum group and related late transition metals. By utilizing a series of characterization techniques, including single-crystal X-ray diffraction, electrospray ionization mass spectrometry, NMR spectroscopy, and computational methods, this work aimed to establish foundational knowledge to inform future application-driven research within this research domain.
Firstly, dianionic sulfonylthiourea ligands were investigated towards platinum(II), revealing a distinct preference for distal isomer (coordinated via S,N-sulfonyl) which was found to be a result of a stabilizing chalcogen bond between thiourea sulfur and sulfonyl oxygen atoms. This non-covalent interaction, confirmed computationally and crystallographically, highlights the potential for modulating isomer selectivity of thiourea ligands through ligand design. Following this study, Chapter 3 extends the investigation of dianionic and monoanionic sulfonylthiourea ligands to organometallic ruthenium(II), iridium(III), and rhodium(III) in the piano stool arrangement. The resulting complexes demonstrated how steric factors influence isomerization and resulting coordination modes. While the proximal isomer persisted among the prepared complexes, using sufficient steric bulk around the metal centre, the distal isomer was formed, exhibiting proximal to distal isomerization in the liquid state. Anticancer assessments against various human cancer cell lines were performed externally which show moderate activity. Trends indicating enhanced efficacy through increased ligand lipophilicity were observed among the ruthenium(II) complexes. In Chapter 4, platinum(II) complexes with dianionic phosphorylthiourea ligands are characterized, revealing a consistent distal isomer preference modulated by bulky substituents. The inclusion of phosphorus atoms onto the ligand enhances characterization capabilities over similar ligands via ³¹P{¹H} NMR spectroscopy, providing a robust tool for elucidating coordination modes. Chapter 5 introduces symmetric diacylated thioureas as versatile ligands for platinum(II), palladium(II), and gold(III). Their coordination mode, forming four-membered S,N coordinated metallocycles, contrasts with the related monoacylated acylthiourea analogues. Moreover, the inclusion of a second acyl group onto the thiourea core allows for additional chalcogen and hydrogen bonding interactions which dominate the structure of the complex. Finally, Chapter 6 presents a ruthenium cymene complex featuring a neutral monodentate diacylthiourea ligand. Non-covalent interaction analysis identifies chalcogen and hydrogen bonding as determining the structural arrangement, reinforcing the importance of these features in future applications.
Collectively, this thesis provides a comprehensive foundation for understanding the coordination chemistry of functionalized thiourea ligands bearing electronegative substituents, opening avenues for their tailored use in fields ranging from catalysis to medicinal chemistry.
Type
Thesis
Type of thesis
Series
Citation
Date
2025-01
Publisher
The University of Waikato
Supervisors
Rights
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