Cyclic voltammetric studies of copper complexes catalyzing atom transfer radical polymerization

Abstract

Several copper complexes used successfully as the catalysts for atom transfer radical polymerization (ATRP) were studied by cyclic voltammetry in acetonitrile. These complexes include CuBr or CuCl complexed by 2,2′-bipyridine (bpy), 4,4′-di(5-nonyl)-2,2′-bipyridine (dNbpy), 4,4′-di(n-nonyl)-2,2′-bipyridine (dnNbpy), N,N,-N ′,N ″,N″-pentamethyldiethylenetriamine (PMDETA), N,- N-bis(2-pyridylmethyl)octylamine (BPMOA), N,N-bis(2-pyridylmethyl)octadecylamine (BPMODA), tris[(2-pyridyl)methyl]amine (TPMA) and tris[2-(dimethylamino)ethyl]amine (Me6TREN), respectively. It was found that the E1/2 value for the redox couple CuI/CuII strongly depends on the nature of the ligand and the halogen. As the number of coordination sites of the ligand increases, the reducing power of the corresponding Cu(I) complex also increases. With the same ligand, CuCl complexes usually have a lower redox potential than CuBr complexes. These general trends agree with the kinetic features of ATRP catalyzed by the corresponding complex, and a correlation between the redox potential and the apparent equilibrium constant of ATRP for methacrylate was observed. The possibility of using electrochemistry as a screening method for selecting ATRP catalysts is therefore further discussed.