Self-assembled Monolayers of N-Heterocyclic Carbenes on Gold and Their Applications

Abstract

N-Heterocyclic carbenes (NHCs) are excellent ligands for metal coordination and have been studied extensively. NHC metal complexes have also been used for many different catalytic applications. One such application of these complexes is their use in water oxidation catalysis as described by Albrecht. In Chapter 2 we will discuss the progress made in tethering water oxidation catalysts to gold surfaces via NHC self-assembled monolayers (SAMs). This project bridges the gap between NHCs for surface science applications and for homogeneous catalysis. Two main routes were explored for this project to immobilize an iridium-based water oxidation catalyst. The catalyst was synthesized either on or off of the NHC SAM support. Several generations of the catalysts were tested for catalytic activity for water oxidation catalysis and this too will be discussed in Chapter 2. Recently it has been shown by the Crudden group and others that NHCs are excellent surface ligands with high stability for Au(111). The preparation of these materials have recently improved using simple benchtop methods, which will be discussed in Chapter 3, instead of generating the free carbene using strong base and inert atmosphere. Hydrogen carbonate salts of NHC precursors were used to deposit an NHC SAM on Au(111) in situ with HPLC methanol. These films were found to have the same characteristics and stability as those deposited using the free carbene. In Chapter 3 we also describe the use of other azolium salts with non-coordinating counterions to deposit NHC SAMs on Au(111) without the need to create the hydrogen carbonate salts. This simplifies the benchtop method even further as ion exchange reactions are no longer necessary for NHC SAM deposition.