Synthesis and reactivity of novel (NHC)gold(I) complexes

Abstract

The fields of N-heterocyclic carbenes and homogeneous gold catalysis have experienced tremendous growth within the last two decades. In addition, the combination of these fields to give NHC-gold complexes has delivered superior stability and reactivity, allowing the isolation of new reactive species and a better understanding of the fundamental chemistry. The work presented in this thesis attempts to synthesise novel NHC-gold complexes and document their reactivities. The main themes discussed in this work are: (a) the understanding and avoidance of silver additives in gold-mediated transformations; and (b) the study of different NHCs to provide optimal sterics and electronics for a given application. In Chapter 2, the reported “Gold(I)-Mediated C-H Activation of Arenes” is investigated. The role of each additive is assessed, and in particular the reliance on silver salts is considered. An NHC ligand was used to stabilise reactive intermediates, which provided new insights into the function of the silver additive. Gold(I) hydroxides are repeatedly shown to be invaluable synthetic equivalents, as well as key intermediates in silver-free protocols. Chapter 3 details numerous attempts to synthesise [Au(OH)(NHC)] complexes that are stable, pure and in high yields. Chapter 4 documents the synthesis of gold species featuring the ITent family of NHC ligands. Their highly flexible steric bulk is investigated by crystallographic studies, and is believed to contribute to their relatively high stabilities. Chapter 5 describes the use of the newly synthesised [Au(OH)(NHC)] complexes to generate mono- and bifluoride species. The reaction conditions were then optimised in order to maximise yields and regioselectivities. Finally, Chapter 6 examines the use of NHC selenium adducts to measure the π-accepting ability of these ligands. These are then coordinated to gold, whereupon different geometries are observed depending on the nature of the NHC.