Homogeneous catalysis in ionic liquids

In the past 15 years, ionic liquids have become an alternative reaction medium for organic transformations, especially for transition metal catalysis. Their unique properties make them ideal solvents for "green" industrial processes: they are polar, thus exhibiting high solubility for a large variety of substrates and catalysts, they are immiscible with many organic solvents, and they do not evaporate in high vacuum. Many of their physicochemical properties are changed substantially by variation of the cation and the anion; thus, they are "tunable" to the desired reaction. This review focuses on the general concepts that are applicable to ionic liquids as reaction media. This knowledge is intended to enable the reader to use ionic liquids advantageously for their chemistry. In the second part, some recent examples of successful ionic liquid solvent chemistry are pointed out and discussed in more detail.