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 × 10⁻³ ∼ 0.5 mol dm⁻³ HCl ( I = 0.5 mol dm⁻³ HCl + NaCl) over a range of temperatures. The kinetic data can be fitted to the rate expression k_obs = k K^′ ₂[H⁺]/(1 + K^′ ₂[H⁺]). The acid dissociation can be rationalized in terms of a six-step kinetic process involving rapid pre-equilibrium cleavage of the two Cu^II–N(aliphatic amine) bonds, two rapid pre-equilibrium protonations and rate-determining cleavage of the Cu^II–N(phenanthroline) bond. The temperature dependence of the rate was determined and the appropriate thermodynamic parameters obtained. [ABSTRACT FROM AUTHOR]