Metal Complexes with Macrocyclic Ligands. Part XXVII . Cu 2+ ‐promoted hydrolysis of carboxylic‐ and phosphonic‐acid esters in the side chain of tetraazamacrocycles

The X‐ray structures of the Cu 2+ 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 Cu 2+ 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.