Abstract
This thesis presents a number of new strategies for redox gold chemistry, which nominally involves the +1 and +3 oxidation states. Results herein demonstrate the reactivity of gold towardselementary organometallic steps, leading to examples of catalytic and stoichiometric reactions.
Following a general introduction to gold chemistry (Chapter 1), Chapters 2 and 3 explore the
reactivity of [R2-bipyAu(C2H4)]+
complexes towards C–I oxidative addition. Previous work in
the group demonstrated oxidative addition of aryl iodides with complexes of this type. Chapter
2 expands the scope of this reaction, where alkenyl and alkynyl iodides were shown to be active.
As with the gold(III) complexes generated from aryl iodides, those derived from alkenyl and
alkynyl iodides undergo stoichiometric cross-couplings with addition of organozinc reagents.
In Chapter 3, the highly adaptable [R2-bipyAu(C2H4)]+
complex allowed investigation into a
number of aspects of the relatively poorly understood oxidative mechanism at gold(I) centres. Electron-poor ligands were found to give faster rates of oxidative addition, opposite to
effects usually observed with palladium. Theoretical [bipyPd(C2H4)] and [bipyPt(C2H4)] complexes gave a significantly more thermodynamically favourable oxidative addition compared to
[bipyAu(C2H4)]+.
Building upon the mechanistic insights provided in Chapter 3, a base-free gold-catalysed
Suzuki-Miyaura cross-coupling reaction was sought. It was envisaged that addition of a phosphine donor atom to gold(I) complexes would give the complex stability required for catalysis.
A number of ligand designs were assessed, with an electron-poor 8-quinolyl phosphine ligand
giving the highest yield of 17%. This (poor) reactivity was found to be due to the formation
of catalytically active gold nanoparticles. These aggregated over time which rendered them inactive. Incompatibilities between silver(I) salts and aryl boronic acids were also demonstrated.
Ultimately, increased cross-coupling in up to 87% yield were observed between aryl iodides and
aryl boronic acid pinacol esters with by application of a hemi-labile NHC gold(I) precatalyst in
Chapter 5. Boronic ester transmetallation under base-free conditions was found to be mediated
by fluoride, most likely generated in situ from AgSbF6.
Finally, Chapters 6 and 7 explore the reactivity of carbon monoxide and isocyanides as ligands for gold complexes. Initially, Chapter 6 describes the synthesis of [bipyAu(CO)]+ and
[bipyAu(C≡N–R)]+
complexes. The [bipyAu(CO)]+
complex showed unusual π-back-donation,
giving a classical gold(I) carbonyl complex. Following these initial investigations, Au(III)–C
migratory insertion of carbon monoxide following C–C bond activation of biphenylene was
explored in Chapter 7. At a MeDalPhos gold(III) metallofluorene complex, reaction mixture
analysis by FTIR, 13C{
1H} NMR spectroscopy, mass spectometry and computational methods
showed that 9-fluorenone is generated via a formal migratory insertion and reductive elimination. Gold(III) migratory insertion complexes were found to have increased thermodynamic
stability compared to those generated from rhodium.
| Date of Award | 2 Dec 2021 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | John Bower (Supervisor) & Chris A Russell (Supervisor) |