Thermodynamic Properties of Copper Complexes Used as Catalysts in Atom Transfer Radical Polymerization

The thermodynamic properties of some copper complexes, among those frequently used as catalysts in controlled/living radical polymerization, has been studied in CH 3 CN + 0.1 M (C 2 H 5 ) 4 NBF 4 . A combination of different techniques, namely potentiometry, spectrophotometry and cyclic voltammetry, has been used to determine the stability constants of all possible complexes of Cu I and Cu II present in binary and ternary systems composed of Cu I or Cu II, a halide ion (X = Cl −, Br − ) and a polyamine ligand (L = pentamethyldiethylenetriamine, tris(2-dimethylaminoethyl)amine). The binary Cu−X systems show only mononuclear CuX x complexes, where x = 1, 2, 3, 4 for Cu II, and x = 1, 2 for Cu I . Conversely, in the case of the binary Cu−L systems, besides the mononuclear complexes CuL l, where l = 1 or 2, also dinuclear complexes Cu 2 L were found. The ternary systems give rise to a mixture of mononuclear and dinuclear complexes of general formula Cu m L l X x . Besides the 1:1:1 complex obtained in all combinations, the following species were found: Cu II LX 2, Cu I 2 LX and Cu I 2 LX 2 . The stability constants of all these species were determined and used to construct speciation diagrams for both Cu I and Cu II species. Such diagrams show that often conditions favoring the quantitative formation of Cu II L, Cu II L 2, or Cu II LX can be easily realized, whereas isolation of a single predominant Cu I species can hardly be achieved. Speciation diagrams for Cu I as a function of C X / C Cu I show interesting results that may be helpful in rationalizing the role of termination reactions in atom transfer radical polymerization.