Kinetics of the substitution reaction between aquo cupric ion and ethylene-bis-N,N′ -(2,6-dicarboxylato)piperidinonickelate(II)

The kinetics of the substitution reaction between aquo cupric ion and the nickel(II) complex of ethylene-bis-N,N′-(2,6-dicarboxy)-piperidine (NiEBDP) have been measured, as well as the equilibrium constants associated with the protonation of the metal ion complexes and the rapid formation of dinuclear complexes. The rate data can be expressed by the following rate law: $\text{−}\text{d[NiEBDP]}{}_{\mathrm{T}}\text{d}\text{t}\text{=}\text{k}{}^{\mathrm{<mtext>NiEBDP</mtext>}}{}_{\mathrm{<mtext>Cu</mtext>}}\text{[Cu}{}^{\mathrm{2+}}\text{]+k}{}^{\mathrm{<mtext>NiEBDP</mtext>}}{}_{\mathrm{<mtext>H</mtext>}}\text{[H}{}^{\mathrm{+}}\text{]+k}{}^{\mathrm{<mtext>NiEBDP</mtext>}}{}_{\mathrm{<mtext>Cu,H</mtext>}}\text{[Cu}{}^{\mathrm{2+}}\text{][H}{}^{\mathrm{+}}\text{]}\text{[}\text{NiEBDP}{}^{\mathrm{2-}}\text{].}$ Values of rate constants (25.0°C, μ = 1.25), enthalpies and entropies of activation for the reaction pathways are: k_Cu^NiEBDP, 2.77 × 10⁻²M⁻¹ sec⁻¹, 11.7 kcal/mole, −26.4 cal mole⁻¹ K⁻; k_H^NiEBDP, 3.33 × 10⁻²M⁻¹ sec⁻¹, 14.8 kcal/mole, −15.6 cal mole⁻¹ K⁻¹; and k_Cu.H^NiEBDP, 4.47 × 10⁺¹M⁻¹, 13.9 kcal/mole, −4.3 cal mole⁻ K⁻¹, respectively. The results are interpreted in terms of steric effects arising from the ring structure of the ligand by comparison to kinetic studies of similar systems.