The Aquation and Base Hydrolysis of Chlorobis(Ethylenediamine)Cobalt(III) Cations Containing Ammonia Derivatives as Orienting Ligands
In the octahedral cobalt(III) system, the most widely studied reactions in aqueous solutions are the solvolytic aquation and the base hydrolysis. Both reactions have been shown to take place by a rearrangement, either SN1 or SN2, between the solvation shell and the coordination shell of the complexes (1, 2). The dependence of the rates of solvolytic aquation of complexes of the type [Co en2 A Cl] n+ (where en = ethylenediamine and A = a variable orientingligand) on the nature of A has led to the postulation of a duality of mechanism for the process (3, 4). Electron-repelling groups facilitate dissociation of the chlorine ligand and give rise to a unimolecular mechanism, while electron-attracting groups assist a bimolecular reaction. For the base hydrolysis of these cations, the assignment of mechanism has been contro - versial. BASOLO and PEARSON ( 5) suggested that an SN1CB mechanism operates involving a pre -equilibrium in which the hydroxide ion removes a proton from one of the amine nitrogens forming an amido conjugate base which then undergoes a rate -determining dissociation of the chloride ion. BROWN, INGOLD and NYHOLM (6) however preferred an SN2 mechanism in which the hydroxide ion directly replaces the chlorine ligand.
KeywordsSolvation Shell Order Rate Constant Coordination Shell Silver Nitrate Solution Base Hydrolysis
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