Dimerization of styrene was investigated in ionic liquids and organic solvents with the catalysis of several palladium-Lewis acids catalyst systems. Pd(OAc)(2)/Cu(OTf)(2) and Pd(OAc)(2)/ln(OTf)(3) in 1-butyl-3-methylimidazolium hexafluorophosphate were found to be effective catalyst systems towards the dimerization of styrene to 1,3-diphenyl-l-butene at room temperature. (c) 2006 Elsevier B.V. All rights reserved.