ABSTRACT
A variety of palladium on activated carbon catalysts differing in Pd dispersion, Pd distribution, Pd oxidation state and water content were tested in Heck reactions of aryl bromides with olefins. The optimization of catalyst and reaction conditions (temperature, solvent, base and Pd loading) allowed development of Pd/C catalysts with very high activity for Heck reactions of non-activated bromobenzene (TON ~ 18,000, TOP up to 9,000, Pd concentrations down to 0.005 mol%). The catalysts combine high activity and selectivity under ambient conditions (air and moisture), with easy separation and quantitative recovery of palladium. Determination of Pd in solution during and after the reaction and catalyst characterization before and after the reaction (TEM) indicate dissolution/re-precipitation of palladium during the reaction. The Pd concentration in solution is highest at the beginning of the reaction and is minimized (« 1 ppm) at the end of the reaction. Pd leaching correlates significantly with the reaction parameters.
