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

Abstract

The aquation of cis-[(en)₂Co(CO₂H)₂]⁺ to cis-[(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 dm ³ mol^{-1 -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.