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 t he introduction of the aqueous two-phase technique. This method uses a homo geneous catalyst dissolved in water. The catalyst separation from the produ cts can be easily achieved by simple phase decantation. Room-temperature io nic liquids based on organic cations, such as dialkylimidazolium, and inorg anic anions, such as AlCl4-, Al2Cl7-, BF4-, PF6- and SbF6-, offer an extens ion to this field especially when substrates, organometallic complexes and ligands are poorly soluble or unstable in water. They present a large spect rum 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 so lvent. Ionic liquids containing weakly coordinating anions such as BF4-, ar e good solvents for Diels-Alder reactions. (C) 1999 Elsevier Science B.V. A ll rights reserved.