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 CuII 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)Cu]⁺, [(en)₂CoCl-(NH₂CH₂CO₂)Cu]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.