Thermomorphic catalysis in microemulsions

Abstract

Ionic liquid based microemulsions have attracted a great deal of interests both in industry and academics due to their potential properties in chemical reactions and their advantages over organic solvents and surfactants. Many studies showed that in the presence of ionic liquids, polar and non-polar phases are not necessarily water and oil for the formation of microemulsion. Moreover, in many cases ionic liquids used as amphiphile molecules to helpthe formation of microemulsions in different environments (aqueous and nonaqueous) due to their unique surface activities. The ability of some ILs to support the self-assembly of amphiphiles is of particular importance since, other than ILs, there is a very limited number of known solvents possessing this capability. The structural variables of ILs include the length of the hydrophobic tail, the nature of the counterion, and the nature/charge of the head-group, allows the possibility of tailoring self-assembly solvents with specific desired properties.In the first part of this thesis, we highlighted the properties of three types of ionic liquid based microemulsions, including nonaqueous IL microemulsion, aqueous IL microemulsion and IL/oil/water microemulsion. Different characterization techniques exploring their properties were investigated in detail. Additionally, in this section we summarize the recent applicationsof the ionic liquid based microemulsions in different fields such as nanomaterial synthesis, reaction media, bio catalysis, drug delivery, polymerization, isolation and extraction.The second part of this thesis focuses on the design, synthesis and characterization of surfaceactive ionic liquids that are able to form stable microemulsions with heptane and water. The obtained surface-active ionic liquids were successfully applied as reaction media for thermomorphicpalladium-catalyzed cross-coupling reactions. High reactivity was observed even at low catalyst loadings, while the temperature-dependent phase behavior allowed simple product separation and successful catalyst recycling through thermomorphic catalysis. A fundamental difference was found between carbene and noncarbene forming ionic liquids, suggesting thatthe ionic liquid can play a dual role as surfactant and ligand.The final part of the thesis addresses the application of the thermomorphic ionic liquid based microemulsion system for the Ru-catalyzed asymmetric transfer hydrogenation of ketones. Based on the temperature-dependent multiphase behavior of the targeted microemulsion, simple product separation as well as catalyst recycling could be realized. The use of watersoluble ligands improved the immobilization of the catalyst in the microemulsion phase and significantly decreased the catalyst leaching into the organic layer upon extraction of the product. Eventually, the optimized microemulsion system could be applied to a wide range of aromatic ketones that were reduced with good isolated yields and enantioselectivities, whilealiphatic ketones were less successful.