Octahedral cobalt(III) complexes of the chloropentammine type. Part VII. The role of haloalkylamines as influencing ligands in hydrolytic reactions of the bis(ethylenediamine)cobalt(III) system

Abstract

The first-order rate constants for the solvolytic aquation of cations of the type cis-[Co en₂(X–RNH₂)Y]²⁺ have been determined at different temperatures and the Arrhenius parameters calculated, where en represents ethylenediamine, X–RNH₂ represents a chloro- or bromo-derivative of ethylamine or n-propylamine, and Y = Cl or Br. This reaction takes place by a bimolecular exchange of species between the solvation shell and the co-ordination shell of the complex. In determining the mechanism of the reaction, the inductive effects of covalent halogens directly joined to the carbon skeletons of the aliphatic amines exert a greater influence than those of the alkyl groups. The second-order rate constants for the base hydrolysis of the chlorine-containing cations have also been determined at 0° and at an ionic strength of 0·1M. These results provide further and unambiguous evidence contrary to the conjugate-base mechanism¹ for the reaction. An S_N1/P mechanism is assigned and, unlike solvolytic aquation, inductive factors of covalent chlorine have little effect on the rate of base hydrolysis of co-ordinated chlorine.