The Heck coupling of iodobenzene with olefins occurs with high efficiencies at low temperatures in imidazolium-based ionic liquids catalyzed by PdCl2/Et3N, and the catalyst can be recycled after extraction of the products by supercritical CO2. The coupling efficiency is dependent on water content of the ionic liquid. With a low water content (< 50 ppm) in the ionic liquid, the Heck coupling reaction would proceed with > 90% yield at room temperature using this catalytic system.