Base hydrolysis of carboxylatopenta-amminecobalt(III) nitrates

Abstract

An extended range of carboxylatopenta-amminecobalt(III) nitrates have been prepared and analysed, and their d–d and charge-transfer spectra have been recorded. The carboxylato groups have been derived from acetic, propionic, isobutyric, mono-, di-, and tri-chloroacetic, trifluoroacetic, trans-crotonic, α-methylacrylic, but-3-enoic, β-methylcrotonic, pent-4-enoic, sorbic, benzoic, diphenylacetic, and trans-cinnamic acids.Velocities for the base hydrolysis of the complexes confirm that the predominant effect of the leaving carboxylato ligand is a polar one, facilitating fission of the cobalt–oxygen bond for those complexes with strongly electron-withdrawing (-I effect) carboxylato ligands. The polar effects and apparent absence of steric effects are consistent with both the main mechanisms proposed for base hydrolysis of cobalt complexes, namely, the SN2 mechanism with trans-attack and the SNICB mechanism. The possible BAC 2mechanism, which has previously been proposed for the trifluoroacetato-complex, is not inconsistent with the present results.