Generally, gold(I) complexes interact with [pi]-bonds of alkenes, alkynes and allenes to initiate nucleophilic addition reactions. As the key intermediates in these reactions, there has been recent interest in the synthesis and study of cationic, two-coordinate gold [pi]-hydrocarbon complexes. However, few experimental studies have been focused on gold [pi]-heteroatom complexes. Moreover, gold(I)-catalyzed reactions may involve protic acids (H+), so it is significant to establish more detailed structure/activity relationships to determine the necessity of applying gold complexes. Previous literature at the outset of these studies focused on methodology explorations and computational investigations, but little experimental elucidation of mechanisms had been done. Alternatively, a "silver effect" is now considered to play a role in some gold(I)-catalyzed reactions, however the direct evidence for Au-Ag species in solution is limited. The first chapter summarizes the development of gold(I)-catalyzed additions of heteronucleophiles to C-C multiple bonds including application in total synthesis. Structural aspects of gold(I)-enol ether complexes and solution behavior of both gold(I)- enol ether and enamine complexes are described in Chapter Two. We showed that the coordination about gold in the solid-state structures of complexes with either a (tBu)3P or JohnPhos ligand are nearly identical, while the rates of exchange of excess enol ether are significantly faster for the former. This led to the conclusion that the kinetic stabilization evident in complexes with an o-biphenyl phosphine ligand is a result of steric shielding rather than an electronic interaction. The strength of coordination for enamines to gold is significantly greater than that of any alkene or enol ether examined to date and this corresponds with significant distortion in the complex.. The high distortion leads to a diminishing of double-bond character in the enamine, and the barrier to rotation has been measured for a geminally disubstituted enamine. This feature suggests that enamine stereochemistry in gold-catalyzed hydroamination reactions is thermodynamically driven. In Chapter Three we isolated a unique diphosphine trimetallic chloronium dication from a Celite prefiltered solution initially thought to be silver-free. The crystal structure also incorporated the coordination to silver of one fluorine atom of one SbF6 - counterion. DFT calculations supported significant silver-halide and silver-arene interactions in the mixed gold/silver complex and moderate metallophilic interactions. Comparison of computed data revealed that the [lower case Greek letter omega]B97X-D functional, which has a long-range corrected hybrid with atom-atom dispersion corrections, gave a better fit to the experimental data compared with the PBE0 functional, which has previously failed to capture aurophilic interactions. Preliminary studies support the presence of the mixed gold/silver structure in solution. Chapter Four presents a mechanistic analysis of trigold oxonium and gold hydroxide mediated intramolecular aurations. We utilized the commercial availability of IPr-Au-OH (IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) to confirm the ability of gold hydroxide to mediate alkyl gold formation. Thus treatment of alkenes containing pendant nucleophiles, with 1 equivalent IPr-Au-OH in CDCl3 at 25 °C resulted in facile formation of the corresponding cyclized alkyl gold. We have hypothesized that these reactions are another instance of what Nolan has referred to as cooperative or "dual activation", whereby the gold complex activates substrate both by coordinating to the double bond and by deprotonating the substrate heteroatom to make it a better nucleophile.