Exploration of N-Heterocyclic Carbenes for the Functionalization of Gold Surfaces and Their Metal Complexes

Gold surface chemistry has progressed considerably towards many applications in medicine. Due to the non-toxic nature of gold in the human body, gold surfaces have been investigated for biometric sensors and targeted drug therapy agents. While gold is relatively unreactive in its elemental form, gold surfaces (such as films or nanoparticles) require a ligand for stability and improved functionality. The typical ligand is thiols for self-assembled monolayers on gold surfaces. While thiol self-assembly on surfaces is well understood, thiols are known to degrade or leach under a wide variety of conditions, including both thermal and chemical, which is toxic in the body. For gold surfaces to be viable in the medical field, the surface ligands must be stable in a multitude of conditions. Thiols’ degradation has resulted in the exploration for more stable ligands. Since N-heterocyclic carbene (NHC) ligands are strong σ-donors, they have the potential to replace thiols. In a short time, utilization of NHCs have greatly advanced the field of gold surface chemistry. These ligands have shown greater stability than thiols under a variety of conditions. Since these ligands are new to surface chemistry, research has not progressed past the traditional imidazolium and benzimidazolium based NHCs. However, variations from the traditional NHC ligands can be more effective in solution phase chemistry. The research presented in this dissertation will focus on synthesis, spectroscopy, and theory to understand the binding of NHCs to gold surfaces. The exploration of non-standard NHC ligands were also explored for functionalization of gold surfaces. The traditional NHC ligands were deuterated and bound to gold surfaces to aid in the assignment of their modes in SERS. Within the non-traditional NHC ligands, an imidazolinium NHC ligand was bound and the stability was tested on gold surfaces to show the first examples of non-standard NHC superior stability over and imidazolium NHC. In addition, using a conjugated six-membered NHC, four d¹⁰ metal complexes were synthesized and characterized through X-ray crystallography and NMR. Finally, a variety of functionalized NHC ligands are in the process of being synthesized for post-synthetic modification on gold surfaces.