Synthesis and characterization of two novel macrocyclic monoxo-tetraamines and the stabilities of their Cu(II) complexes

The synthesis and characterization of two novel macrocyclic monoxo-tetraamines: 1,4,7,10-tetraazacyclotridecane-2-one (1) and 1,4,8,11-tetraazacyclotridecane-5-one (2) are described. Equilibrium constants for their Cu(II) complexes were determined by direct potentiometry. The formation constants (KML=[MH−1L]/[M][L][H−1]) of Cu(II)-1 in 0.10 M KCl at 25.0 °C is 1011.09; that for the 2 isomer is 1010.58. The results are compared with the corresponding constants of a known ligand 3 (2-oxocyclam, KML=1012.97). The pMs (pM −log [Cu2+] at 25 °C, μ=0.10 M KCl with 100% excess ligand at pH 7.4) of ligands 1–3 are 16.3, 15.2 and 17.3, respectively. The results are also compared with some dioxomacrocyclic tetraamines.