Kinetics and mechanism of the acid-catalyzed hydrolysis of [carbonatotetra(1-methylimidazole) cobalt(III)]+ ion

The kinetics of acid-catalyzed hydrolysis of the [Co(1-Meim)(4)(CO3)](+) ion follows the rare law -d In[complex]/d t = k(1)K[H+]/(1 + K[H+]) (25+45 degrees C, [H+] = 0.05+1.0 M and I = 1.0 M (NaClO4)). The reaction course consists of a rapid pre-equilibrium protonation followed by a rate determining ring opening process and the subsequent fast release of monodentate carbonate ligand. Kinetic parameters, k(1) and K, at 25 degrees C are 5.1x10(-3) s(-1) and 0.48 M-1 respectively, and activation parameters for k(1) are Delta H-1(not equal) = 84.4 +/- 0.8 kJ mol(-1) and Delta S-1(not equal) = -5.8 +/- 3.7 J mol(-1) K-1. The hydrolysis rate increases with the ionic strength. The results are compared with those for similar cobalt(III) complexes.