Kinetics and mechanism of ligand exchange reaction of copper(II) complexes with tetradentate Schiff base ligands.

The kinetics of a ligand exchange in the CuL4/H2Ln system, where H2Ln is the N,N'-alkylen-bis(salicyldimine) tetradentate Schiff base ligand (n = 2 or 3, CH2 groups in the chain length of the amine backbone) was studied spectrophotometrically in DMF solvent with or without triethylamine (NEt3) and H2O at 25 ± 0.1 °C and an ionic strength of 0.01 M NaNO3. The reaction rate was found to be first-order with respect to CuL4 complex and H2Ln ligand. The rate of the ligand exchange reaction did not change significantly with the addition of H2O to the DMF solvent; however, it increased when NEt3 was added to the reaction mixture. The effect of NEt3 and H2O on the ligand exchange rate shows that the deprotonation/protonation of the H2Ln ligand and anionic form of H2Ln are essential to the reaction. A reaction mechanism is proposed and discussed for the effect of NEt3 and H2O on the ligand exchange rate.