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.