Metal ion catalysed aquation of carboxylatoamine cobalt(III) complexes. Kinetics of copper(II) catalysed aquation ofcis(diformato)bis(ethylenediamine)cobalt(III) ion

Summary

The aquation ofcis-[(en)₂Co(CO₂H)₂]⁺ tocis-[(en)₂Co(OH₂)(CO₂H)]²⁺ is catalysed by Cu²⁺ and the rate equation, −d[complex]_t/dt=(k_Cu[Cu²⁺]+k_H [H⁺]) [complex)_T is valid at [Cu²⁺]_T=0.01–0.1, I=0.5 and [HClO₄]=0.005 mol dm⁻³. The rate measurements are reported at 30, 35, 40 and 45°C and the rate and activation parameters for the Cu²⁺ and H⁺-catalysed paths are: k_H(35°C)=(2.44±0.09)×10⁻² dm³ mol⁻¹ s⁻¹, ΔH^‡=83±13 kJ mol⁻¹, ΔS^‡=−8±42 JK⁻¹ mol⁻¹, k ^′_Cu (35°C)=(3.30±0.09)×10⁻³ dm³ mol⁻¹ s⁻¹, ΔH^‡=73.2±6.1 kJ mol⁻¹, ΔS^‡=−55±20 JK⁻¹ mol⁻¹. The formate-bridged innersphere binuclear complex,cis-[(en)₂Co{(O₂CH)₂Cu}]³⁺ may be involved as the catalytically active intermediate in the copper(II)-catalysed path, just as the corresponding H⁺-bridged species presumed to be present in the acidcatalysed path.