Tridentate nitrogen-based ligands in Cu-based ATRP:: A structure-activity study

The kinetic parameters for the activation and deactivation steps in ATRP for Cu-based catalysts were determined with eight different tridentate nitrogen-based ligands. Additionally, the redox properties of these Cu complexes were measured by cyclic voltammetry. By correlating the kinetic parameters of the activation and deactivation steps with the reduction potential of the Cu(II) complexes, it was found that more reducing Cu catalysts form faster activating Cu(I) and slower deactivating Cu(II) species. The rate of activation depends on the nature of the N-binding site of the ligand. Ligands with alkyl amine or pyridine binding sites form the fastest activating catalysts. The phenyl-substituted ligands form very slowly activating and very rapidly deactivating catalysts. Slower deactivation rates were found for catalysts with a central pyridine unit in the ligand than for catalysts derived from ligands with a central amine unit. In general, the activity of the ligands decreases in the following order: alkyl amine approximate to pyridine > alkyl imine much greater than aryl imine > aryl amine.