Cyclic voltammetric studies of copper complexes catalyzing atom transfer radical polymerization

Several copper complexes used successfully as the catalysts for atom transf er radical polymerization (ATRP) were studied by cyclic voltammetry in acet onitrile. 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'-bip yridine (dnNbpy), N',N ",N "-pentamethyldiethylenetriamine (PMDETA), N,-N-b is(2-pyridylmethyl)octadecylamine (BPMOA), N,N-bis(2-pyridylmethyl]octadecy lamine (BPMODA), tris[(2-pyridyl)methyl)amine (TPMA) and tris[2-(dimethylam ino)-ethyl]amine (Me6TREN), respectively. It was found that the E-1/2 value for the redox couple Cu-I/Cu-II strongly depends on the nature of the liga nd and the halogen. As the number of coordination sites of the ligand incre ases, 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 o f ATRP catalyzed by the corresponding complex, and a correlation between th e redox potential and the apparent equilibrium constant of ATRP for methacr ylate was observed. The possibility of using electrochemistry as a screenin g method for selecting ATRP catalysts is therefore further discussed.