Lanthanide complexes of chiral 3+3 macrocycles derived from (1R,2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol

The enantiopure amine macrocycle H3L, as well as the parent macrocyclic Schiff base H(3)L1, the 3 + 3 condensation product of (1R, 2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol, are able to form mononuclear complexes with lanthanide(III) ions. The lanthanide(III) complexes of H3L have been studied in solution using NMR spectroscopy and electrospray mass spectrometry. The NMR spectra indicate the presence of complexes of low C-1 and C-2 symmetry. The H-1 and C-13 NMR signals of the Lu(III) complex obtained from H3L have been assigned on the basis of COSY, TOCSY, NOESY, ROESY and HMQC spectra. The NMR data reveal unsymmetrical binding of lanthanide(III) ion and the presence of a dynamic process corresponding to rotation of Lu(III) within the macrocycle. The [Ln(H4L)(NO3)(2)](NO3)(2) (Ln = Sm(III), Eu(III), Dy(III), Yb(III) and Lu(III)) complexes of the cationic ligand H4L+ have been isolated in pure form. The X-ray analysis of the [Eu(H4L)(NO3)(2)](NO3)(2) complex confirms the coordination mode of the macrocycle determined on the basis of NMR results. In this complex the europium(III) ion is bound to three phenolate oxygen atoms and two amine nitrogen atoms of the monoprotonated macrocycle H4L+, as well as to two axial bidendate nitrate anions. In the presence of a base, mononuclear La(III), Ce(III) and Pr(III) complexes of the deprotonated form of the ligand L3- can be obtained. When 2 equivalents of Pr(III) are used in this synthesis Na-3[Pr2L(NO3)(2)(OH)(2)](2)NO3 center dot 5H(2)O is obtained. The NMR, ES MS and an X-ray crystal model of this complex show coordination of two Pr(III) ions by the macrocycle L. The X-ray crystal structure of the free macrocycle H(3)L1 has also been determined. In contrast to macrocyclic amine H3L, the Schiff base H(3)L1 adopts a cone-type conformation resembling calixarenes.