New chiral receptors based on dibenzotetraaza[14]annulenes

Reactions of dibenzotetraaza[14]annulene Ni(II) complexes 1 and 2 with oxal yl chloride and chiral terpene alcohols ((-)menthol, (-)borneol), and the C inchona alkaloid (quinine) afforded new mono and disubstituted derivatives bearing corresponding ester groups at the meso positions. The demetallation of di(-)menthyloxycarbonyl and di(-) bornyloxycarbonyl derivatives has bee n accomplished by means of gaseous HCl, leading to corresponding free bases . Single-crystal X-ray diffraction of the free ligand equipped with two (-) menthyloxycarbonyl substituents revealed a saddle-like shape of the molecul e resulting in the non-equivalence of two axial coordination sites of the m acrocycle. The (-) menthyloxycarbonyl substituents were found to define the 'walls' of a cavity on one side of the macrocyclic platform. The two menth yl rings belonging to the meso substituents appeared to be non-equivalently arranged on both propanediiminate parts of the macrocycle, relative to the ir phenyl and methyl substituents. The molecules of the ligand are arranged in stacking columns and form cavities in the crystal lattice. The molecule s of solvent (benzene) were found to reside in these cavities. The amine pr otons of the central tetraaza fragment of the macrocycle are involved in tw o asymmetric intramolecular N-H . . .N hydrogen bonds. The H-1 and C-13 NMR spectra measured at room temperature, in CDCl3 solution, provided evidence of conformational non-equivalence within both meso-disubstituted propanedi iminate fragments of the macrocycle. Additionally, two non-equivalent NH pr otons have been detected in the H-1 NMR spectra of both free ligands. The n ew products have been characterized by elemental analyses, ESI MS, IR, H-1 and C-13 NMR data. (C) 2001 Elsevier Science B.V. All rights reserved.