Octahedral cobalt(III) complexes of the chloropentanimine type. XXX. The thallium(III)-induced aquation of some cis-Halogeno(amine)bis(ethylenediamine)cobalt(III) cations in aqueous solution

Abstract

The second-order rate constants for the thallium(III)-induced aquation of cis-[Co(en)₂(RNH₂)Cl]²⁺ cations, where R is H, Me, Et, Prⁿ, and Prⁱ, have been measured in aqueous solution over a range of temperatures, and the activation parameters calculated. The kinetic results are discussed in terms of a rapid pre-equilibrium formation of an activated complex Co-Cl-Tl, followed by a simple rate-determining aquation in which TlCl²⁺ acts as the leaving group, although the alternative possibility of a rate-determining attack by Tl³⁺ cannot be excluded. In the case of R = H, the investigations have been extended to the corresponding bromo cation which reacts some 50 times faster than its chloro analogue.