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

Il lavoro descrive la sintesi e caratterizzazione di due nuovi leganti macrobiciclici. Inoltre sono state studiate le proprietà coordinative di questi due leganti nei confronti dello ione Li(I) attraverso misure potenziometriche, tecniche NMR. The synthesis of the novel macrobicyclic ligands 44,​9-​dimethyl-​41,​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 consts. of L2, together with those of the macrobicycles L4 and L5, have been potentiometrically detd. both in water and in water-​DMSO mixt. (80:20, vol.​/vol., NaCl 0.15 mol dm-​3, 298.1K)​. Coordination of Li+ by these macrobicycles has been studied by means of 13C and 7Li NMR techniques. All ligands bind Li+ in aq. soln., 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 consts. of the lithium complexes have been detd. in water and in water-​DMSO mixt. (80:20, vv, NaCl 0.15 mol dm-​3, 298.1 K) by means of potentiometric measurements.