Synthesis and characterization of cross-bridged cyclams and pendant-armed derivatives and structural studies of their copper(II) complexes

A series of 1,4,8,11-tetraazabicyclo[6.6.2]hexadecane ligands, including th e parent compound, N,N'-dialkyl variants, and the first N,W-di-pendant-arm derivatives have been synthesized by a short, efficient, and conceptually n ovel approach. Their copper(II) complexes have been prepared, and four of t hese were structurally characterized by X-ray diffraction. in all four comp lexes, the cross-bridged tetraamine ligand was found to be cis-folded, coor dinating the metal cation within its molecular cleft using all four nitroge n lone pairs. Geometries intermediate between idealized square pyramidal an d trigonal bipyramidal coordination were found for three of the complexes, whereas a distorted octahedral copper coordination was found for the comple x of a dipendant-arm cross-bridged cyclam.