Synthesis, characterization, electrochemical studies, and ATRP activity of a series of novel copper(I and II) complexes with TPMA-based ligands containing 4-methoxy-3,5-dimethyl-substituted pyridine arms were reported. In the solid state, Cu-I(TPMA*(1))Br, Cu-I(TPMA*(2))Br, and Cu-I(TPMA*(3))Br complexes were found to be distorted tetrahedral in geometry and contained coordinated bromide anions. Pseudo-coordination of the aliphatic nitrogen atom to the copper(I) center was observed in Cu-I(TPMA*(2))Br and Cu-I(TPMA*(3))Br complexes, whereas pyridine arm dissociation occurred in Cu-I(TPMA*(1))Br. All copper(I) complexes with substituted TPMA ligands exhibited a high degree of fluxionality in solution. At low temperature, Cu-I(TPMA*(1))Br was found to be symmetrical and monomeric, while dissociation of either unsubstituted pyridine and/or 4-methoxy-3,5-dimethyl-substituted pyridine arms was observed in Cu-I(TPMA*(2))Br and Cu-I(TPMA*(3))Br. On the other hand, the geometry of the copper(II) complexes in the solid state deviated from ideal trigonal bipyramidal, as confirmed by a decrease in t values ([Cu-II(TPMA*(1))Br][Br] (t = 0.92) > [Cu-II(TPMA*(3))Br][Br] (t = 0.77) > [Cu-II(TPMA*(2))Br][Br] (t = 0.72)). Furthermore, cyclic voltammetry studies indicated a nearly stepwise decrease (Delta E approximate to 60 mV) of E-1/2 values relative to SCE (TPMA (-240 mV) > TPMA*(1) (-310 mV) > TPMA*(2) (-360 mV) > TPMA*(3) (-420 mV)) on going from [Cu-II(TPMA)Br][Br] to [Cu-II(TPMA*(3))Br][Br], confirming that the presence of electron-donating groups in the 4 (-OMe) and 3,5 (-Me) positions of the pyridine rings in TPMA increases the reducing ability of the corresponding copper(I) complexes. This increase was mostly the result of a stronger influence of substituted TPMA ligands toward stabilization of the copper(II) oxidation state (log beta(I) = 13.4 +/- 0.2, log beta(II) = 19.3 (TPMA*(1)), 20.5 (TPMA*(2)), and 21.5 (TPMA*(3))). Lastly, ARGET ATRP kinetic studies show that with more reducing catalysts an induction period is observed. This was attributed to slow regeneration of CuI species from the corresponding CuII.