Optical Resolution of rac-5,5,7,12,12,14-Hexamethyl-1,4,8,11-tetraazacyclotetradecane (L), Circular Dichroism Spectra of Ni(II) Complexes with the Active Ligand, and the Absolute Configuration of (−)589-[{Ni(SS-L)}2(d-tart)(H2O)](ClO4)2·2H2O as Determined by the X-Ray Analysis

The title ligand (L) has been resolved through its d-tartrato-nickel(II) complex. The X-ray analysis shows that the less-soluble (−)589-diastereomer has a dimer structure with the folded macrocycles, [{NiL}2(d-tart)(H2O)](ClO4)2·2H2O, and that the chiral carbon atoms have the absolute configuration of S. Axial methyl groups of geminal dimethyl pairs of each nickel (II) complex in the dimer provide stereoselective environment for the coordination site of the d-tartrate ion. Stereospecific hydrogen-bonds between a secondary amine group of the macrocyclic ligand or coordinated water and hydroxyl or carboxyl oxygens of the d-tartrate ion play also an important role in the optical resolution. Pairs of enantiomers of the free ligand and three isomers of the four-coordinate nickel(II) complex have been isolated. Circular dichroism spectra of various four- and six-coordinate complexes with the optically active ligand have been described.