A highly effective, easy to handle and environmentally benign process for a palladium mediated Heck reaction was developed. The in situ prepared 3-component system, Pd( OAc)(2) / 1,3-dialkylbenzimidazolium chlorides ( LHX = 1a-g) and Cs2CO3, catalyzes quantitatively the Heck coupling of aryl bromides under mild conditions in aqueous media.