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

Abstract

The kinetics of aquation and base hydrolysis reactions ofcis-[(en)2Co(imH)O2CC6H4OH-o-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\(\left( {k_{obs} = k_{H_2 O} + k_H \left[ {H^ + } \right]} \right)\). 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 kobs = kb + kb° [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.