Chiral metal complexes 38. Coordination control in complexes of an optically active macrocyclic ligand

Abstract

The macrocyclic complex [Cu( S-mac)] 2+, where S-mac is 6 S,16S-(14 R,14 R-dimethyl)-1,5,11,15-tetraazatricyclo-[14,4,1,1 6,11]docosane, has been synthesized stereospecifically using a template reaction and reduction of an intermediate diimine. Reduction of the diimine was achieved in quantitative yield and proceeds with absolute stereospecificity, as far as can be practically determined. The single-crystal X-ray structure of the complex, as its anhydrous diperchlorate salt, has been determined at low temperature. Crystal data: C 20H 40N 4O 8Cl 2Cu is orthorhombic, space group P2 12 12 1, with a=8.350(2), b=12.525(3), c=24.817(7) Å, Z=4. The structure was refined by full-matrix least-squares methods to R=0.041 for 2025 non-zero reflections. Each cation is five-coordinate with square-based pyramidal geometry, formed by the four nitrogen donors of the macrocycle in the square plane, and an oxygen atom (two partially occupied positions) of a disordered perchlorate ion (CuO 2.442(9), 2.401(21) Å). Both carbon atoms attached to the methyl groups of the macrocycle have absolute configuration R. Folding of the seven-membered rings of the ligand produces a conformation such that only one face of the complex is available for axial coordination of unidentate ligands. The complex has been demetallated. The free ligand thus generated reacts with Cu(II) to give a complex which has all features of the original stereochemistry preserved. Analogous Ni(II) and Pd(II) complexes have also been prepared and characterized using NMR techniques.