Asymmetric Catalysis in Ionic Liquids with ‘Unmodified’ Catalysts
Since the late 1960s metal-catalysed enantioselective transformations have become one of the most studied fields in synthetic chemistry. This area has seen the advancement of a vast array of new catalysts based on various metals and ligands. More recently, due to environmental and toxicity constraints placed upon the chemical industry, the choice of solvent has also become important. Reaction engineering and recycling of the catalyst systems has become standard practice with the use of liquid-liquid biphasic systems or grafting of the catalysts onto solid supports two of the main techniques employed. In some cases this has resulted in poor catalyst performance or catalyst leaching. Recently, ionic liquids have provided the means to tune catalytic processes, and even more importantly, immobilize the catalyst and facilitate recycling. This chapter discusses the concept of homogeneous supported catalysis in ionic liquids for enantioselective reactions.