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 derivatives, 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 †

Diels-Alder reactions in neutral ionic liquids (such as 1-butyl-3methylimidazolium trifluoromethanesulfonate, 1-butyl-3methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium lactate) are reported. Rate enhancements and selectivities similar to those of reactions performed in lithium perchlorate-diethyl ether mixtures have been observed. As the ionic liquids used have no measurable vapour pressure, are thermally robust, will tolerate impurities such as water, and are recyclable, it is envisaged that these systems could be used on an industrial scale.

The room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF 6 ], is used as a 'green' recyclable alternative to dipolar aprotic solvents for the regioselective alkylation at the heteroatom of indole and 2-naphthol.

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Alkyl-3-methylimidazolium tetrachloropalladate(II) salts ([C n -mim] 2 [PdCl 4 ], n~10, 12, 14, 16, 18) containing a single, linear alkyl-chain substituent on the cation have been synthesised and their behaviour characterised by differential scanning calorimetry, polarising optical microscopy and small-angle X-ray scattering. The salts display thermotropic polymorphism, exhibiting both crystal±crystal transitions and, for n~14±18, the formation of a thermotropic smectic liquid crystalline phase.