Br?nsted acid?base ionic liquids (GILs) based on guanidine and acetic acid are efficient reaction media for palladium-catalyzed Heck reactions.They offer the advantages of high activity and reusability. GIL2 plays multiple roles in the reaction: it could act as solvent, as a strong baseto facilitate a-hydride elimination, and as a ligand to stabilize activated Pd species.