New macrocyclic dioxotetraamines bearing 2-methylfuran pendant(s): synthesis, properties and crystal structure of the copper(II) complexes

A series of new macrocyclic dioxotetraamine ligands having 2-methylfuran pendent(s), 4-(2-methylfuran)-1 ,4,7,10-tetraazacyclotridecane-11,13-dione (H2L1), 4,7-bis(2-methylfuran)-1,4,7,10-tetraazacyclotridecane-11,13-dione (H2L2), 1-(2-methylfuran)-1,4,8,11-tetraazacyclotetradecane-5,7-dione (H2L3) and 1,11-bis(2-methylfuran)-1,4,8,11-tetraazacyclotetradecane-5,7-dione (H2L4), have been synthesized and characterized. The solution behaviours of the copper(II) complexes of the four ligands have been studied with ESR, cyclic voltammetry (CV) and UV-vis techniques. A red-shift has been observed for the maximum absorption band of the electronic spectra of CuL1, CuL3 and CuL2, CuL4 in comparison to those of the corresponding unsubstituted copper(II) complexes CuL01 and CuL02, respectively. Electrochemical studies suggest that the introduction of 2-methylfuran pendant(s) to the macrocyclic dioxotetraamines destabilizes the Cu-III ion comparing with the unsubstituted species for both of the two kinds of macrocycles (13-membered and 14-membered macrocycles). The copper(II) complex of H2L2 has been isolated as a single crystal and the crystal structure determined by X-ray diffraction analysis. It is interesting that the complex has an N-meso chiral nitrogen configuration. The Cu-II atom is in five coordination environment with four basal nitrogen atoms and one axial oxygen atom from H2O, and it adopts a distorted square pyramidal configuration. (C) 1997 Elsevier Science Ltd.