Recent developments in the use of non-aqueous ionic liquids for two-phase catalysis

One of the most important recent developments in homogeneous catalysis is the introduction of the aqueous two-phase technique. This method uses a homogeneous catalyst dissolved in water. The catalyst separation from the products can be easily achieved by simple phase decantation. Room-temperature ionic liquids based on organic cations, such as dialkylimidazolium, and inorganic anions, such as AlCl4-, Al2Cl7-, BF4-, PF6- and SbF6-, offer an extension to this field especially when substrates, organometallic complexes and ligands are poorly soluble or unstable in water. They present a large spectrum of physical and chemical properties which can be adjusted at will to a given catalytic organic reaction. Nickel catalyzed butene dimerization has been recently developed using chloroaluminate based ionic liquids as the solvent. Ionic liquids containing weakly coordinating anions such as BF4-, are good solvents for Diels-Alder reactions. (C) 1999 Elsevier Science B.V. All rights reserved.