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 S_N2 mechanism with trans-attack and the S_NICB mechanism. The possible B_AC 2mechanism, which has previously been proposed for the trifluoroacetato-complex, is not inconsistent with the present results.