Kinetics and mechanism of elimination of chloride from cis-chlorobis-(ethylenediamine)(glycinato-N)cobalt(III) ion: a study of copper(II)-ion catalysis

Abstract

The rate of elimination of chloride from the cis-chlorobis(ethylenediamine)(glycinato-N-)cobalt(III) ion has been studied under varying conditions of pH and copper(II) concentration in a medium of constant ionic strength of 0·3M. Copper(II) has been found to catalyse the reaction via formation of the binuclear species [(en)₂CoCl-(NH₂CH₂CO₂)Cu]³⁺. The product of the reaction in the presence and absence of Cu^II has been identified as the cis-bis(ethylenediarnine)(glycinato-ON)cobalt(III) chelate. At 50 °C the rate constant, activation enthalpy, and entropy for loss of chloride ion from [(en)₂CoCl(NH₂CH₂CO₂)]⁺, [(en)₂CoCl(NH₂CH₂CO₂H)]²⁺, and [(en)-CoCl(NH₂CH₂CO₂)Cu]³⁺ species are: (2·65 ± 0·03)× 10^–5 s^–1, 90·4 ± 1·7 kJ mol^–1, –54·1 ± 5·4 J K^–1 mol^–1; (1·27 ± 0·01)× 10^–5 s^–1, 92·5 ± 1·3 kJ mol^–1, –53·1 ± 3·3 J K^–1 mol^–1; and (2·74 ± 0·10)× 10^–4 s^–1, 88·3 ± 2·9 kJ mol^–1, –41·0 ± 9·2 J K^–1 mol^–1, respectively. Co–Cl Bond breaking is tentatively suggested to be rate limiting for the loss of chloride ion from all the three species mentioned above.