title: The Electrochemical Oxidation of Metallic Gold and Application to the Synthesis of Gold(I) Tertiary Phosphine Complexes
Creators: name: Bott, Raymond Clinton
Publisher: name: Griffith University
Year: 1998
Subjects: subject: Electrochemical oxidation
subject: Metallic gold
subject: Gold(I) phosphine compounds
subject: Complexes
subject: NMR studies

description: This thesis presents research investigating the electrochemical oxidation of gold into non-aqueous media and application to the preparation of gold(I) phosphine compounds. The processes occurring at the electrode surface during the oxidation of gold metal were investigated using surface enhanced FT-Raman scattering spectroscopy (SERS) and cyclic voltammetry (CV). The effects of oxidation on the gold electrode surface were studied using scanning electron microscopy (SEM) to observe surface profiles and species before and after oxidation. From SERS and CV results, the oxidation of gold involved the formation of a gold chloride surface layer which dissolved into the bulk solvent to complex with the phosphine ligands. A range of tertiary aryl and alkyl phosphine gold(I) halide complexes (PR3AuX, X = C1, Br, I) were synthesised by electrochemical techniques and by reaction of the tertiary phosphines with the gold(I) salts, tetrabutylammonium dihaloaurate(I) ([NBu4][AuX2], X = C1, Br, I). The simplest electrochemical cell without a too great a loss of efficiency and product yield was found to be a batch type. Complexes were characterised using FT-Raman (FTR), solution and solid state 31P-{1 H}-NMR, and single crystal X-Ray crystallographic (XRD) studies. As expected, for an increase in the gold halide bond length (of similar complexes with the same halide), both Raman and NMR studies displayed a decrease in the frequency and chemical shifts from the chloride to iodide complexes respectively. The behaviour of gold ions in HCI acidified acetonitrile or propylene carbonate solutions were studied using proton decoupled phosphorus-31 nuclear magnetic resonance spectroscopy (31P- {1 H} NMR). Titration of 1,2-bis(diphenylphosphino)ethane (dppe) by slowly electrochemically dissolving gold into the acetonitrile or propylene carbonate was followed using 31P-{1 H) NMR and used to study the reaction equilibria of gold(I) phosphine systems formed as the gold chloride layers dissolved into acetonitrile or propylene carbonate solutions. 31P-{1 H} NMR studies in acetonitrile were conducted at 38 +- 2 degrees C to prevent the precipitation of the 2:1 (Au:dppe) gold(I) chloride dppe complex. To prevent precipitation of this complex at ambient temperatures, propylene carbonate was used in place of the acetonitrile. Variable temperature 31P-{1 H} NMR studies were used to resolve various broad peaks observed in the propylene carbonate system. These studies displayed the initial formation of the 1:2 (Au:dppe) gold(1) chloride dppe complex. As gold was added to this system, an equilibrium was formed between the tetrahedral complex, the 1:1 (Au:dppe) annular complex, and the 2:1 (Au:dppe) bridged complex. A small amount of ligand oxidation was observed which resulted in the formation of gold(I) chloride dppe monoxide complex.