Roberts, Dean and McLaughlin, Mark (2024) Synthesis of Diverse Metalloid Scaffolds via Transition Metal Catalysis. PhD thesis, Lancaster University.
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Abstract
The work within this thesis describes developments in platinum catalysed hydrometallation for the synthesis of a range of diverse metalloid scaffolds. Chapter 1 contains a discussion of the application of organometalloid scaffolds in modern organic chemistry, as well as the widespread application of platinum complexes in the synthesis of said scaffolds. Notable developments in the field are summarised and the generally accepted mechanisms through which these reactions proceed are discussed. Chapter 2 examines the limitations of previous platinum complexes in catalysing selective hydrosilylations and the reasons for these limitations, as well as discussing the approaches to, and applications of, allylic amines in organic chemistry. The development of a PtCl2Xantphos catalyst to selectively carry out the hydrosilylation of propargylic amines and their derivatives is detailed as well as an investigation of the substrate scope. The synthetic utility of the products is investigated resulting in the development of a remarkably mild aziridination procedure. Chapter 3 builds on the previous aziridination procedure, demonstrating the applicability of the same sequence to access a range of diverse oxetanes by a hydrosilylation/cyclisation sequence. Previous approaches to oxetanes are discussed, as well as the utility of the scaffold in modern organic and medicinal chemistry. Attempts to expand the methodology to the synthesis of other heterocycles is also discussed. Chapter 4 details the study of platinum complexes in the context of hydrostannylation chemistry. Previous approaches to the scaffold are discussed, as well as the surprising lack of platinum-based catalyst systems. The effect of ligand denticity on stereoselectivity is reported, with a ligand controlled stereodivergency reported. Using a PtCl2(XPhos)2 catalyst system, a range of diverse organotin scaffolds are synthesized, and the benefits and limitations of the system in comparison to previous catalysts is discussed. A telescoped hydrometallation/cross-coupling sequence is developed to minimize the need to handle relatively unstable and toxic stannylated intermediates. Chapter 5 explores the application of platinum complexes bearing both NHC and phosphine ligands as hydrosilylation catalysts. The synthesis of a broad range of imidazolium salts is presented, alongside the synthesis of several platinum complexes via an organosilver intermediate. The efficacy of the complexes towards hydrosilylation is evaluated, and their poor performance rationalized in the context of similar complexes employed in the literature. Chapter 6 provides overall conclusions from the work presented as well as a discussion of further avenues of study. Chapter 7 provides bibliographic data for the thesis. Relevant characterisation data for novel compounds or compounds prepared by novel routes can be found at the end of the relevant chapter.