New oxidants for arylations with gold
Item statusRestricted Access
Embargo end date30/11/2021
Pagett, Alexander Brenan
Gold as an element, has been known for tens of thousands of years, though only recently has the chemistry of gold complexes emerged as an important field for synthetic organic chemistry research. One significant challenge when investigating the chemistry of gold complexes is the oxidation of gold(I) to gold(III), gold(I) having a very high oxidation potential. This thesis comprises an investigation of gold through a homogeneous oxidative arylation of arenes using arylsilanes. Chapter 2 examines the nature of ligands on gold through a gold catalysed arylation reaction and the application of this to synthesise chiral biaryls. The investigation realises that strongly coordinating L type ligands inhibit catalyst turnover and discovers that transient, enantiopure, chiral additives have no effect on the distribution of enantiomers of the chiral biaryl. Chapter 3 explores new, inorganic oxidants for the oxidation of gold(I) to gold(III) and investigates aryl iodide cocatalysts for gold catalysed arylation. It is discovered that periodic acid allows turnover of the gold catalyst and produces a biaryl product from an arylsilanes substrate. Through MALDI-MS, gold is also discovered to react with acetonitrile in the presence of periodic acid, in a novel oxidative reaction for gold, to form a gold(I) cyanide polymer. In Chapter 4, NMR kinetics and stoichiometric experiments are utilised in the investigation of mechanistic details of periodic acid as an oxidant for gold catalysed direct arylation. The six-electron reduction pathway for periodic acid to an iodonium species and the mechanism of formation of aryl iodide from the starting arylsilane is probed. Iodonium is proposed to be the intermediate that forms the aryl iodide byproduct. Further evidence for a reactive iodonium species is found using a chemospecific, nucleophilic trap that prevents the non-productive iodination of aryl silane. A substrate scope of the new arylation conditions using the trap is assessed and the reaction was found to tolerate substrates that generated 5 membered rings. This thesis aims to establish new conditions for gold catalysed arylation of arenes using arylsilanes and describes interactions of oxyiodine species with arylsilanes, nitrile solvents and gold.