Kinetics of acid-catalysed dissociation of N,N '-dialkyl-1,10-phenanthroline-2,9-dimethanamine copper(II) complexes

The kinetics of the acid-catalysed dissociation of Cu-II complexes of four N,N'-dialkyl-1,10-phenanthroline-2,9-dimethanamine ligands (alkyl = Me, Et, i-Pr, t-Bu) have been studied using a stopped-flow spectrophotometer in 6. 6 x 10(-3) similar to 0.5 mol dm(-3) HCl (I = 0.5 mol dm(-3) HCl + NaCl) ov er a range of temperatures. The kinetic data can be fitted to the rate expr ession k(obs) = kK(2)'[H+]/(1 + K-2'[H+]). The acid dissociation can be rat ionalized in terms of a six-step kinetic process involving rapid pre-equili brium cleavage of the two Cu-II-N(aliphatic amine) bonds, two rapid pre-equ ilibrium protonations and rate-determining cleavage of the Cu-II-N(phenanth roline) bond. The temperature dependence of the rate was determined and the appropriate thermodynamic parameters obtained.