σ-Bonded organotransition-metal ions. Part XI. Kinetics and mechanism of the reactions of pyridiomethylpentacyanocobaltate(III) ions with thallium(III), mercury(II), indium(III), and gallium(III) chloride in aqueous acid

Abstract

The kinetics and products of the reaction of thallium(III) and mercury(II) chloride with the 2-, 3-, and 4-pyridiomethylpentacyanocobaltate(III) ions have been studied as a function of the chloride-ion concentration in aqueous acid. Thallium(III) chloride displaces the pentacyanocobaltate(III) group, whether chloride ion is present or not, to give the corresponding monopyridiomethylthallium(III) chloride ion by a bimolecular (S_E2) process. Mercury(II) chloride displaces the pentacyanocobaltate(III) group by an analogous reaction only in the presence of added chloride ion. In the absence of added chloride ion, and to some extent in the presence of low concentrations of chloride ion, the mercury(II) chloride assists in the removal of a cyanide ligand to give the aquopyridiomethyl-tetracyanocobaltate(III) ion, which is much less reactive towards electrophilic substitution than is the pyridiomethylpentacyanocobaltate(III) ion. Indium(III) and gallium(III) chloride do not react with the pyridiomethyl-pentacyanocobaltate(III) ion in the presence of added chloride ion but, in the absence of added chloride ion, they complex with, and assist in the removal of, one of the cyanide ligands. The rate coefficients for the reaction of the individual chloro-mercury(II) and -thallium(III) species have been calculated and compared with those for the reaction of the same species with the penta-aquopyridiomethylchromium(III) ions.