Structural and mechanistic studies of co-ordination compounds. Part 16. Preparation and acid hydrolysis of trans-bromo- and trans-chloro-nitrocobalt(III) complexes of 2,3-dimethyl-1,4,8,11-tetra-aza-cyclotetradeca-1,3-diene and 2,3,9,10-tetramethyl-1,4,8,11-tetra-aza-cyclotetradeca-1,3,8,10-tetraene

Abstract

The complexes trans-[CoX(L)(NO₂)]ⁿ⁺[L = 2,3-dimethyl-1,4,8,11-tetra-azacyclotetradeca-1,3-diene (L¹), X = Cl^– and Br^–; and L = 2,3,9,10-tetramethyl-1,4,8,11-tetra-azacyclotetradeca-1,3,8,10-tetraene (L²), X = Cl^–, Br^–, NCS^–, or OH₂] have been prepared and the acid hydrolysis of the halogeno-compexes has been investigated. The specific rates of acid hydrolysis of these nitro-complexes are nearly independent of the extent of unsaturation in the amine macrocycles, whereas K_Br/K_Cl decreases. The order of the labilizing power of A (A = Cl, N₃, NCS, or NO₂) on the acid hydrolysis of trans-[CoX(L)A]⁺(X = Cl or Br) gradually changes with the extent of unsaturation in L [L = L³(1,4,8,11-tetra-azacyclotetrdecane, cyclam). L⁴(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane), L¹, and L²]. In L² complexes, the order becomes very similar to that for the base hydrolysis of trans-[CoCl(L³)A]⁺. This observation suggests that unsaturation in macrocyclic amines and amido-groups in amine conjugate bases have similar effects in promoting the hydrolysis of cabalt(III) complexes.