Kinetics and mechanism of hydrolysis of cis-bis(ethylenediamine)imidazole(salicylato)cobalt(III) ion

Abstract

The kinetics of aquation and base hydrolysis reactions of cis-[(en)₂Co(imH)O₂CC₆H₄OH-o]²⁺ (imH = imidazole) have been investigated in a medium of 1.0 M ionic strength, In the 0,1-1,0 M [H⁺] range (60-70°) aquation proceedsvia spontaneous and acid catalysed paths ( k_obs = kH₂O + k_H[H⁺]). In the 0,05-1.0 M [OH^-] range (30-40°), the complex exists predominantly as the bis-deprotonated species,cis-[(en)₂Co(im)O₂CC₆H₄O-o], and the pseudo-first-order rate constant fits the relationship k_obs = k_b + k_b^OH [OH^-] satisfactorily. The labilizing action of coordinated imidazolate anion(im^-) on the cobalt(III)-bound salicylate is 10³ times stronger than that of imidazole. The mechanism is essentially Id in the aquation paths and SN₁cb (Co-O bond fission) in the alkali independent and dependent paths respectively.