Simple method for enhancement of the ligand-free palladium catalyst activity in the Heck reaction with non-activated bromoarenes

Simple catalytic system is reported capable of catalyzing effectively the reaction of bromoarenes with styrene in air in the absence of any ligands. Quantitative yield of the product was achieved by the use of 0.04–1.6 mol% PdCl 2 , 18% HCOONa, 112% AcONa and six-fold excess of bromoarene (with respect to styrene) in DMF after 10 min at 140° or after 180 min at 100°. Confirmation was obtained of the earlier reported assumption that colloid palladium particles formed in the course of the reaction are the main “reservoir” of catalytically active homogeneous Pd(0) complexes.