Electrochemical study of the effect of Al3+ on the stability and performance of Cu-based ATRP catalysts in organic media

Electrochemically-mediated atom transfer radical polymerization (eATRP) has attracted a great deal of attention as one of the most powerful methods of synthesis of polymers with well-defined architecture and low dispersity. The process is more cost-effective and simpler if performed in undivided cells with cheap sacrificial anodes such as aluminum. In this connection, knowledge of the effect of Al3+ ions released from the anode on the stability and performance of typical Cu catalysts is highly desired. In this study, the stability of Cu complexes with tris(2-(dimethylamino)ethyl)amine (Me6TREN) and tris(2-pyridylmethyl)amine (TPMA), was investigated in DMF, DMSO, and MeCN by cyclic voltammetry, UV-vis-NIR spectroscopy and controlled-potential eATRP. Both ligands form complexes with Al3+, but in DMF and DMSO, TPMA binds more strongly to Cu2+ and Cu+ than Al3+, whereas the opposite is true for Me6TREN in all tested solvents. Therefore, eATRP of n-butyl acrylate catalyzed by [CuITPMA]+ in DMF or DMSO was not affected by Al3+ ions. In contrast, when Me6TREN was used, the reactions could not proceed to high conversions because Al3+ ions displace Cu2+ from the ligand. To suppress the effect of Al3+, use of excess ligand and/or Br− with respect to CuII proved to be efficient.