Synthesis of planar chiral rhodium(II) paddlewheel catalysts : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Chemistry at Massey University, Manawatū, New Zealand
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2024
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Massey University
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Catalysts are the most efficient tools for the construction of large complex molecules. They offer an unparalleled way to solve problems and new ways to build molecules. Site-selective catalysts control the site of reaction in molecules that contain multiple sites with similar reactivity. C-H groups are the most abundant sites in all organic molecules but are very unreactive and difficult to functionalise. C-H functionalisation catalysis aims to install functionality at these sites by replacing the C-H bond with a C-C, C-O, C-N or C-X bond. Controlling the selectivity of these reactions is extremely difficult but highly rewarding, as it allows complex molecules to be made from very simple starting materials. Rh(II) paddlewheels are a class of selective C-H functionalisation catalysts that are capable of highly site-selective and enantioselective transformations. The organic ligands of the complex create different shapes around the catalyst active site that force a single C-H site to be targeted. This project aimed to synthesise a new class of Rh(II) paddlewheel catalysts that possess a planar chiral ligand and to investigate their activity and selectivity in C-H insertion reactions. In this work a novel resolution route for dibromide [2.2]paracyclophane carboxylic acids was developed. The carboxylic acids ligands were then used to synthesise three Rh(II) catalysts. Two of these paddlewheels were used to develop a late-stage catalyst functionalisation method through Suzuki-Miyaura coupling. In total, five Rh(II) catalysts were synthesised, of which four were assessed in both intermolecular and intramolecular nitrene insertion reactions.