Charged Up With Closo-Carborane Anions: Chemical Synthesis of Ionic Materials in Ligand Design and Transition Metal Chemistry
- Author(s): Fisher, Steven P
- Advisor(s): Lavallo, Vincent
- et al.
The beginnings of boron rich nanoclusters chemistry are in part due to the pioneering work of Alfred Stock. It was Stock’s air sensitive syntheses that paved the road to many pyrophoric borohydrides. Surprisingly some of these pyrophoric borohydrides were found to be useful starting materials for synthesizing the extremely stable closo-carborane anions. Once assembled these polyhedral clusters are composed of mostly boron atoms with at least one carbon atom and are about a nanometer in length. Due to their great stability these anionic nanoclusters have become well known as weakly coordinating anions. This is largely due to the fact that the negative charge is delocalized over the entire polyhedral cluster and that chemist have been able to isolate extremely reactive cations using these anions. However, the applications of these boron rich nanoclusters is not limited to their ability to act as weakly
coordinating anions but has extended into the fields of medicine and material sciences. One field of study is using these materials as anions tethered to ligand scaffolds, with these anionic scafolds chemist have been able to create metal complexes and, in some cases, even produce state of the art catalyst. The primary focus of this thesis is to explore the use of an anionic boron rich nanoclusters as ligand a substituent/s in N-heterocyclic carbenes (NHC) ligands. The story begins with the synthesis of an unsymmetrical NHC bearing one N-bound anionic boron rich nanocluster and one N-bound aryl group. This synthesis proved to be modular accommodating multiple boron rich nanoclusters and aryl groups. To prove that the anionic NHC salts were viable ligands for coordination chemistry a set of anionic and zwitterionic Au(I) complex were generated. These results showed that these ligands are viable and that the Au(I) complexes are catalytically active for hydroamination chemistry. Envisioning a bimetallic system where the anionic Au(I) complex was coulombically bound to a metal cation lead to the formation of a bimetallic Au(I)/Ag(I) complex. This bimetallic complex was tested as a halide abstracting reagent. Indeed this halide abstracting reagent is capable of chloride abstraction from transition metal complexes. As a proof of principle crystal structures were obtained for Au-/Rh+ and Au-/Ru+ systems. Lastly anionic Au(I) complexes with main group cations is reported. These cations include Ph3C+, R3Si+ and a borenium cation.