Reaction of copper(I) chloride pyridine complexes with dioxygen. A kinetic study

Summary Copper(I) complexes [CuClL]₂ (L=Py, 4-PhPy, 4-MePy, 4-Me₂NPy, and 4-PhCOPy) react with dioxygen in dichloromethane according to the rate law: r=K_D^1/2 k₂ [CuClL]₂^1/2[O₂] where KD is the dissociation constant of the equilibrium [CuClL]₂ 2 CuCIL and k₂ the second order rate constant of the reaction of the latter with dioxygen.The K_D values were determined by molecular weight measurements in dichloromethane and a correlation has been developed between the experimental rate constants obtained and the acid dissociation constants (pK_a) for the ligands. The reaction fits a Hammett linear free energy relationship and the rate-determining step is attributed to the first electron transfer to the dioxygen molecule from the mononuclear copper(I) complex, which is influenced by changes in the electron density on the copper.