Gold(III) complexes are of interest due to their potential as antitumor agents. A series of [Au(en)]³⁺ complexes have been prepared. [Au(en)Cl₂]Cl·₂H₂O was used as a starting material for most reactions. It is soluble in water, only slightly soluble in ethanol, and hydrolyzes at pH 3.9 and above. This project consisted of three parts. In the initial studies, depurination was observed in acidic solutions of 2'-deoxyguanosine (dGuo) and 2'-deoxyguanosine-5'-monophosphate (dGMP) in the presence or absence of [Au(en)Cl₂]⁺. In the presence of [Au(en)Cl₂]⁺, product was also formed immediately; this suggested the reaction might have progressed with unprotonated dGuo or dGMP. The competing depurination reaction of unreacted protonated dGuo and dGMP in the mixture was observed over time regardless of the presence of [Au(en)Cl₂]⁺. According to ¹H NMR solution studies [Au(en)Cl₂]⁺ bonds to the N7 of dGuo, dGMP, and guanosine-5'-monophosphate (GMP), each in a 1:1 mole ratio with [Au(en)Cl₂]⁺. Although reaction was immediate in each case upon addition, attainment of equilibrium was slow in some cases. Elemental analysis of the solids obtained from the reaction of [Au(en)Cl ₂]OTf with GMP revealed the formula [Au(en)(GMP]OTf, confirming it was a 1:1 complex. In contrast elemental analysis suggested the reaction with dGMP corresponded to the [Au(en)(dGMP)₂]Cl₃ complex rather than the [Au(en)(dGMP)]Cl₃ formula suggested by ¹H NMR spectroscopy. The second study investigated the reactivity of [Au(en)Cl₂]⁺ with the bridging ligands (4,4'-bipyridine (4,4'-bipy), trans-1,2-bis-(4-pyridyl)ethylene ( tBPE), and GMP) to determine if cyclic species could be obtained. Protonation of the nitrogens of 4,4'-bpy was also observed in crystals obtained from reactions of [Au(en)Cl₂]⁺ and 4,4'-bpy in acidic aqueous solutions. The use of non-aqueous solutions or higher pH provided some stabilization of the ligands (dGuo, dGMP, 4,4'-bpy). ¹H NMR and IR spectroscopy of the complexes formed with [Au(en)Cl₂] ⁺ gave details of complexation to the ligands. [Au(en)Cl₂] ⁺ reacted with tBPE or 4,4'-bpy to form multiple species and the possible formation of a cyclic complex after extended periods of time. Each of the complexes formed with tBPE or 4,4'-bpy exhibited a ¹H NMR spectrum typical for a symmetric structure, indicating each of the nitrogens of the bridging ligand was bonded to [Au(en)Cl₂]⁺. In the third study Na[AuCl ₄] was mixed with 1,2-bis(diphenylphosphino)ethane (dppe) to form a white crystalline solid that corresponded to a 3:2 Au(III)–dppe complex according to its elemental analysis. ¹H NMR solution studies indicated a complex was formed, however the type of complex in solution was unknown. [Au(en)Cl₂]NO₃ was synthesized in order for reactions to be performed in non-aqueous solutions. Its structure was obtained by the single-crystal X-ray diffraction method. The complex has square planar geometry about Au(III) and the anionic NO₃ is located in the apical position and at a distance of 2.999(5) Å´ (compared to 2.2667(18) and 2.2833(17) Å´ for the coordinated Cl^-). The compound belongs to the space group Pbca with a = 10.3380(11) Å´, b = 8.2105(7) Å´, c = 19.625(2), and Z = 8.