Control of Pd leaching in Heck reactions of bromoarenes catalyzed by Pd supported on activated carbon

Parameters that influence the palladium leaching during and after Heck reactions of aryl bromides with olefins catalyzed by heterogeneous Pd on activated carbon systems are reported. Pd leaching correlates significantly with the progress of the reaction, the nature of starting materials and products, solvent, base and atmosphere. The Pd concentration in solution is highest at the beginning of the reaction and is reduced when the reaction is finished. Reaction procedures were developed that allow easy and practicable control and minimization of the Pd leaching at the end of the reaction: Pd re-deposition by: (i) increased temperature, (ii) addition of reducing agents and (iii) working under inert conditions. The Pd concentration in solution after the reaction is reduced to 0.05 ppm Pd (μg Pd/g solution). The catalyst meets all demands for practical application: high activity and selectivity under ambient conditions, complete separation (filtration) of Pd from the product mixture, easy recovery of Pd and commercial availability.