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 the parent compound, N,N‘-dialkyl variants, and the first N,N‘-di-pendant-arm derivatives have been synthesized by a short, efficient, and conceptually novel approach. Their copper(II) complexes have been prepared, and four of these were structurally characterized by X-ray diffraction. In all four complexes, the cross-bridged tetraamine ligand was found to be cis-folded, coordinating the metal cation within its molecular cleft using all four nitrogen lone pairs. Geometries intermediate between idealized square pyramidal and trigonal bipyramidal coordination were found for three of the complexes, whereas a distorted octahedral copper coordination was found for the complex of a di-pendant-arm cross-bridged cyclam.