Cu2+ recognition by N,N′-benzylated bis(amino amides)

Abstract

Two new C 2 -symmetric N , N ’ -benzylated bis(amino amides) have been synthesised and their interaction with di ff erent transition metals studied using a variety of techniques including UV-Vis and CD spec- troscopy or ESI-MS. The determination of the corresponding stability constants with Cu 2+ has been possi- ble, in H 2 O/CH 3 CN 7/3 v/v, for one of these ligands ( 4 ) using potentiometric titrations. The results obtained reveal that N -benzylation a ff ords signi fi cant changes to their properties and is accompanied by an appreciable decrease in the corresponding complexation stability constants. However, this, along with the low kinetics associated to Ni 2+ , facilitates the recognition of Cu 2+ by 4 that can be followed by the naked-eye up to the submillimolar range. Very interestingly, the chiral nature of this ligand provides an intense and well de fi ned CD curve for the corresponding Cu 2+ complex, very sensitive to the coordination geometry, facilitating the analysis of this interaction even at the μ M range. The formation by both ligands ( 3 and 4 ) of square planar complexes with Cu 2+ and Ni 2+ displaying a 1 : 1 stoichiometry was con fi rmed by their X-ray crystal structures