Metal Complexes with Macrocyclic Ligands. Part XXVII. Cu2+-promoted hydrolysis of carboxylic- and phosphonic-acid esters in the side chain of tetraazamacrocycles

The X-ray structures of the Cu²⁺ complexes of 1,4,8,11-tetraazacyclotetradecane derivatives with an ethylpro-pionate and diethylphosphonate group, 5 and 6 , respectively, indicate that the metal ion is pentacoordinated by the four N-atoms of the macrocycle and one O-atom. In the case of 5 , it is the carbonyl O-atom of the carboxylate group, whereas for 6 it is the phosphonyl O-atom of the phosphonate group. The hydrolysis kinetics of the functional group in the Cu²⁺ complexes with the 1,4,8,11-tetraazacyclotetradecanes 3 – 6 have been measured by pH-stat and stopped-flow techniques. The rate law for the hydrolysis of the carboxylates 3 – 5 is proportional to the complex concentration and to OH^?] up to pH 13, whereas that of the phosphonate 6 is proportional to OH^?] up to pH 11.5, becoming independent of OH^?] at pH > 11.5. The mechanisms of these two reactions are discussed, considering the possibility of an intra- or an intermolecular OH^? attack and the results of the X-ray structure analyses.