β-Cyclodextrin-basierte N-Heterocyclische Carben- Gold(I)-Komplexe

Abstract

The concept of sustainability is a broadly investigated topic in the modern organic chemistry which gains more and more importance and affects the development of novel strategies. According to green chemistry, an important issue of catalytic reactions is the recyclability of the catalyst and a simple separation of products. As a method for catalyst recycling, the use of water as solvent is utilized and the recovery of the hydrophilic catalyst can be achieved by extraction of the hydrophobic products, allowing the reuse of catalyst in the aqueous media. To enable water-solubility of a gold catalyst, the research of this thesis is focused on the combination of NHC ligands with a β-cyclodextrin moiety, and on the use of the novel water soluble β-cyclodextrin-NHC-gold complexes in gold-catalyzed transformations in water. Besides modular construction of β-cyclodextrin-NHC-gold complexes, click chemistry as an alternative approach was demonstrated. The binding of the two molecular building blocks was carried out by copper- and ruthenium-catalyzed azide-alkyne cycloaddition. The diversity of the gentle conditions were used to synthesize further β-cyclodextrin-NHC-gold complexes via 1,3-dipolar cycloaddition. In addition, initial results on the catalytic activity and reusability of the catalysts in aqueous media by investigation of gold-catalyzed cycloisomerizations were presented. Furthermore bifunctional β-Cyclodextrin-tagged compounds bearing a SiFA moiety (SiFA = silicon-fluoride-acceptor) were synthesized, which can be applied in positron emission tomography. Moreover, kinetic studies on the rate determining step of the gold-catalyzed cycloisomerization of α-functionalized allenes were performed with various phosphine- and phosphit catalysts in organic solvents.