The reaction of C,N-coordinated gold(III) dihalides; BpAuCl₂ (Bp = 2 benzylpyridyl), AnpAuCl₂ (Anp = 2 anilinopyridyl) and TypAuCl₂ (Typ = 2 tolylpyridyl) with catecholate ligands in hot methanol and trimethylamine produced metallacycles with structural isomers of the general formula (C,N)Au{O,O}. Similarly, BpAuCl₂ and AnpAuCl₂ were reacted with thiourea ligands to form complexes giving high yield and good purity with the general formula (C,N)Au{PhNCSNR₂}+, by means of the addition of BPh₄- for precipitation. X-ray crystal structures of the compounds [AnpAu{PhNCSNMe₂}]BPh₄ and [AnpAu{PhNCSNCy₂}]BPh₄ confirmed the coordination of the thiourea to the gold centre through the N and S atoms. In both cases the geometry around the gold atom is square-planar with complex [AnpAu{PhNCSNCy₂}]BPh₄ showing a slightly more puckered conformation than [AnpAu{PhNCSNMe₂}]BPh₄ due to the sterically bulky cyclohexyl groups attached. Some thiourea derivatives were tested against P388 murine leukaemia cells with complex [AnpAu{PhNCSNHPh}]BPh₄ showing promising anti-tumour activity. When thiourea ligands were replaced by dithiophosphinate and dithiophosphate ligands the reaction proceeded at room temperature without the need for the presence of a base. Relatively low yields of impure metallacycles with the general formula (C,N)Au{S₂PR₂}+ were obtained on the addition of BPh₄- or BF₄-. Attempts to improve purity by varying batches of starting materials, anion and solvents used were unsuccessful. X-ray crystal data from a single crystal of [(C,N)Au{S₂PPh₂}]BPh₄ shows the reduction of gold(III) to gold(I) forming a known polymeric gold(I) dithiophosphinate complex. In order to extend this study the synthesis of complexes with the general formula R₂PS₂AuCl₂ was attempted, but no new compounds were characterised. Where possible, all new compounds reported in this thesis were characterised by ES-MS, IR, NMR, melting point and micro-elemental analysis.