UBC Theses and Dissertations
Novel bonding motifs in low-valent nickel complexes : Dewar, Chatt, and Duncanson revisited He, Weiying
The classic Dewar-Chatt-Duncanson (DCD) model describes the bonding in transition metal-olefin complexes. In this framework, electron density can be bidirectionally relocated through binary frontier orbital interactions: σ donation and π back donation. Modern spectroscopic and theoretical methods have allowed us to probe the boundary of the framework of this bonding pattern, indicative of the existence of unique DCD model metal complex derivatives. The introduction of this thesis is developed in Chapters 1 & 2, illustrating both the historical context for the development of the DCD model, and its utility in investigating catalyst transfer polycondensation with Ni(0) catalysts in polymer science. Chapter 3 & 4 describe our initial studies using advanced synchrotron-based X-ray absorption spectroscopic methods to comprehensively re-examine this classic electronic structure and provide a framework for the interpretation of synchrotron spectroscopy of nickel complexes. These studies reveal the importance of ancillary ligands to enable strong metal-olefin bonding via ligand-induced backbonding. Insights from these systematic studies afforded the opportunity to examine its relevance in catalytically-relevant systems. Chapter 5 reveals how these insights could be leveraged to stabilize previously elusive analogs of the previously proposed Ni(0) π intermediate in catalyst transfer polycondensation of polythiophenes. The dynamic behaviour of these π -intermediates along the delocalized polymer backbone, i.e. so-called ring-walking along the polymer chain , is explored both via experimental and computational methods. An additional example of DCD-like bonding with unique properties is explored in Chapter 6, where a unique agostic interaction is identified and explained in some low-valent linear Ni(I) complexes, whose electronic structure provides a previously unreported mode of agostic bonding. The application of advanced physical methods to classic problems in organometallic chemistry has afforded new insights into such systems, and revealed new motifs for metal-ligand bonding. These findings provide new opportunities to exploit these bonding motifs in the design of novel organometallic species for catalysis and materials development.
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