Beneficial Combination of Ionic Liquids and Carbon Dioxide in Transition Metal Catalysed Reactions

Compressed carbon dioxide (liquid or supercritical scCO2) and ionic liquids (ILs) are finding a constant interest as alternative green solvents for chemical reactions. Both systems have been employed alone as replacement of volatile organic compounds (VOCs) in a large number of stoichiometric and catalytic transformations sometimes leading to surprisingly improved results. The non volatility of ionic liquids and the benign nature of carbon dioxide are the major driving forces to their use as reaction media. Moreover, the tunability of their solvent properties by proper design (ILs) or by variation of pressure and temperature (scCO2) is an additional reason to their broader application. Both ionic liquids and carbon dioxide present some challenges but, ever since several researchers started to deeply investigate the phase behaviour of the combined system, it appeared how this may possibly be the way to overcome their limitations. The beneficial combination of the two non-traditional solvents has been confirmed by the numerous examples reported in the literature. With the present review the authors wish to discuss about the combination of ionic liquids and carbon dioxide applied to transition metal catalysed reactions with particular emphasis on the phase behaviour of the system.