Aza-macrocycles bearing lipophilic functions. Their synthesis and selective lithium complexation

Abstract

The synthesis of the novel macrobicyclic ligands 4^4,9-dimethyl-4^1,4,7,9-tetraaza-1(1,4)-benzena-4(1,7)-cyclododecanacyclohexaphane (L2) and 5-dodecyl-12,17-dimethyl-1,5,9,12,17-pentaazabicyclo[7.5.5]nonadecane (L3) is reported. The protonation constants of L2, together with those of the macrobicycles L4 and L5, have been potentiometrically determined both in water and in water DMSO mixture (80 : 20, v/v, NaCl 0.15 mol dm^–3, 298.1 K). Coordination of Li⁺ by these macrobicycles has been studied by means of ¹³C and ⁷Li NMR techniques. All ligands bind Li⁺ in aqueous solution, while the other alkali metal ions are not complexed. Lithium complexation is achieved through the encapsulation of the metal ion into the cavity of the macrobicycle. The remarkable selectivity is due to the small dimension of the macrobicyclic cavity, in which only Li⁺ can be lodged. The stability constants of the lithium complexes have been determined in water and in water-DMSO mixture (80:20, v/v, NaCl 0.15 mol dm^–3 298.1 K) by means of potentiometric measurements.