The Heck Reaction in Ionic Liquids: A Multiphasic Catalyst System Adrian J. Carmichael, † Martyn J. Earle,* John D. Holbrey, † Paul B. McCormac, and Kenneth R. Seddon ‡ School of Chemistry, The Queen’s UniVersity of Belfast, Stranmillis Road, Belfast, Northern Ireland, U.K., BT9 5AG m.earle@qub.ac.uk Received July 1, 1999 ABSTRACT Heck coupling of aryl halides or benzoic anhydride with alkenes can be performed with excellent yields in room-temperature ionic liquids, which provide a medium that dissolves the palladium catalyst and allows the product and byproducts to be easily separated. Consequently, the catalyst and ionic liquid can be recycled and reused. The Heck reaction is of major importance in synthetic organic chemistry, as a carbon-carbon bond-forming reaction. 1 It is often used to functionalize aromatic rings and as an alternate to the Friedel-Crafts reaction. 2 The Heck reaction usually involves the interaction of an aromatic halide 3 or anhydride 4 with an alkene, in the presence of a palladium catalyst at typically a 1-2 mol % concentration, to give an aryl alkene. The reaction normally requires a base to be present, 5,6 particularly in the reactions of aryl halides (but not anhydrides). 4 A major problem with the Heck reaction is that the palladium catalyst is often lost at the end of the reaction. 6 Hence, a process for recycling the catalyst system is of importance. Room-temperature ionic liquids have been used to great effect as solvents for a number of reactions, for example, Friedel-Crafts reactions, 7 isomerizations of fatty acid de- rivatives, 8 dimerization reactions of alkenes, 9 Diels-Alder reactions, 10 and hydrogenation reactions. 11 Ionic liquids such as 1-butyl-3-methylimidazolium hexafluorophosphate 12 ([bmim][PF 6 ]) have a particularly useful set of properties, being virtually insoluble in water and alkanes but readily dissolving many transition metal catalysts. 13 Such biphasic ² The QUESTOR Centre, The Queen’s University of Belfast, Stranmillis Road, Belfast, Northern Ireland, U.K., BT9 5AG. ‡ The QUILL Centre, The Queen’s University of Belfast, Stranmillis Road, Belfast, Northern Ireland, U.K., BT9 5AG. (1) (a) Dieck, H. A.; Heck, R. F. J. Org. Chem. 1975, 40, 1083. (b) Kim, J.-I. I.; Patel, B. A.; Heck R. F. J. Org. Chem. 1981, 46, 1067. (c) Bender, D. D.; Stakem, F. G.; Heck, R. F. J. Org. Chem. 1982, 47, 1278. (2) Olah, G. A. Friedel-Crafts Chemistry; Wiley-Interscience: New York, 1973. (3) Namyslo, J. C.; Kaufmann, D. E. Synlett 1999, 114. (4) Stephan, M. S.; Teunissen, A. J. J. M.; Verzijl, G. K. M.; Vries, J. G. de Angew. Chem. Int. Ed. Engl. 1998, 37, 662. (5) Jeffery, T.; J. Chem. Soc., Chem. Commun. 1984, 1287. (6) Shaughnessy, K. H.; Hamann, B. C.; Hartwig, J. F. J. Org. Chem. 1998, 63, 6546. (7) Adams, C. J.; Earle, M. J.; Roberts, G.; Seddon, K. R. Chem. Commun. 1998, 2097. (8) Adams, C. J.; Earle, M. J.; Hamill, J.; Lok, C. M.; Roberts, G.; Seddon, K. R. World Patent WO 98 07679, 1998. (9) (a) Ellis, B.; Keim, W.; Wasserscheid, P. Chem. Commun. 1999, 337. (b) Einloft, S.; Olivier, H.; Chauvin, Y. U.S. Patent US 5550306, 1996. (10) Earle, M. J.; McCormac, P. B.; Seddon, K. R. Green Chem. 1999, 1, 23. (11) (a) Fisher, T.; Sethi, A.; Welton, T.; Woolf, J. Tetrahedron Lett. 1999, 40, 793. (b) Adams, C. J.; Earle, M. J.; Seddon, K. R. Chem. Commun. 1999, 1043. (12) Huddleston, J. G.; Willauer, H. D.; Swatloski, R. P.; Visser, A. E.; Rogers, R. D. Chem. Commun. 1998, 1765. (13) Dullius, J. E. L.; Suarez, P. A. Z.; Einloft, S.; De Souza, R. F.; Dupont, J.; Fischer, J.; De Cian, A. Organometallics 1998, 17, 815. ORGANIC LETTERS 1999 Vol. 1, No. 7 997-1000 10.1021/ol9907771 CCC: $18.00 © 1999 American Chemical Society Published on Web 09/16/1999