Exploring the synthesis and metal complexation behavior of mono and bis substituted hexaazamacrocyclic cage derivatives

A series of new hexaazamacrobicyclic cage ligands were synthesized and their metal complexation was investigated. Ligands synthesized included the benzyldiamsar, 4-bromobenzyldiamsar, 4-hydroxybenzyld iamsar, 4-methoxybenzyldiamsar, 4-(1-hydroxyethyl)benzyldiamsar, 4-nitrobenzyldiamsar bis-(benzyl)diamsar, bis-(4-bromobenzyl)dia msar, bis-(4-hydroxybenzyl)diamsar, bis-(4-methoxybenzyl)diamsar, bis-(4-(1-hydroxyethyl)benzyl)diamsar, bis-(4-nitrobenzyl)diamsar and bis-(4-aminobenzyl)diamsar. The complexation of the new ligands with Cu(II) and Co(II) at micromolar concentrations was performed at pH 39 and ambient temperature. All ligands complexed the Cu(II) rapidly within 5 min over the pH range 59. The complexation of Co(II) by the new ligands was significantly slower with optimum rate at pH 78 at ambient temperature. The substituents on the benzyl group of the new ligands was found to influence the formation of the Co(II) complexes, with the bis derivatives found to be comparatively slower. In contrast, the substitutents of mono- and bis-(4-substituted-benzyl)- hexaaza cages did not impact the rate of complexation of Cu(II). Overall the metal complexation was influenced by the desolvation energy of the metal ions as well as the substituents on the benzyl group. Nonetheless, the complexation study demonstrates that these new ligands could be Inorganic Chemistry Communications 82 (2017) 4851 ⁎ Corresponding authors. E-mail addresses: [email protected] (E. Mume), [email protected],(C. Papamicaël). used both with Cu(II) and Co(II) at micromolar concentrations for further applications that require a physiological pH and ambient temperature