Medium effect on the reactions of complexes: kinetics and mechanism of the base hydrolysis of cis-[(salicylato)(amine)bis(ethylenediamine)cobalt(III)] compounds in methanol-water

Abstract

The kinetics of base hydrolysis of cis-[(salicylato)(RNH2) (en)2COIII]2+ (R = H, Me or Et) have been studied in MeOH-H2O medium at 35.0°C, I = 0.1 (ClO 4 − ) and 0.01 ⩽ [OH-]Tmol dm-3 ⩽ 0.10. The phenoxide species [(RNH2)(en)2CoO2C6H4O]+, underwent both OH--independent (SNICB) and OH--catalysed (SN1CB) hydrolysis with K obs=k 1+k 2[OH−]. Both k 1 and k 2 are appreciably enhanced by the medium for MeNH2 and EtNH2 complexes. In contrast, for the NH3 complex, k 1 decreases with increasing MeOH content and k 2 was non-existent beyond 60% (v/v) MeOH. These rate variations illustrate the importance of the solute-solvent interaction, presumably partly of hydrophobic origin, and solvent structure in existing stabilizing/destabilizing effects on the initial and transition states.