An efficient and recyclable dendritic catalyst able to dramatically decrease palladium leaching in Suzuki couplings

A series of novel monomeric and dendritic thiazolyl phosphines (generations 1 and 3) was prepared and the activity these ligands conferred to palladium in Suzuki couplings was evaluated. The heteroaryl ligands were revealed to be very efficient and were able to perform the reactions in mild conditions. Besides, their efficiency was compared to that of the corresponding triphenylphosphines. Moreover, the possibility to reuse both families of dendritic ligands was explored and the thiazolyl phosphine-based catalytic systems could be successfully recycled for five consecutive reactions without loss of activity, contrary to their triphenylphosphine counterparts. Remarkably, the palladium leaching was found to be dramatically reduced by using the dendrimer-supported thiazolylphosphines instead of the monomeric ligand and only trace amounts of metal (<0.55 ppm) could be found in the coupling product before any purification.