Structural and mechanistic studies of co-ordination compounds. Part XI. Preparation and acid hydrolysis of some octahedral cobalt(III) complexes of meso-1,4,8,11-tetra-aza-5,5,7,12,12,14-hexamethylcyclotetradecane and -tetradeca-1,7-diene

Abstract

The preparation and characterization of trans-[CoL′(A)Br]⁺(I; L′=meso-1,4,8,11-tetra-aza-5,5,7,12,12,14-hexamethylcyclotetradecane; A = N₃ and NCS) and trans-[CoL″(A)X]ⁿ⁺(II; L″=meso-1,4,8,11-tetra-aza-5,5,7,12,12,14-hexamethylcyclotetradeca-1,7-diene; A = OH₂, N₃, and NCS; X = Cl and Br) cations are described. The acid hydrolysis of the azido- and isothiocyanato-cations has been studied over a range of temperature. The ratio of the rate constant with bromide to that with chloride as leaving group, k_Br : k_Cl, at 25 °C is ca. 10 : 1 for complexes (I) but decreases to ca. 2 : 1 for (II), independent of the nature of the orienting ligands A. This observation is consistent with the proposition that the relative ‘softness’ of the central cobalt(III) ion increases in going from complexes (I) to (II).