BIMETALLIC REACTIVITY - GENERAL-SYNTHESIS OF BINUCLEATING MACROCYCLICLIGANDS CONTAINING 6-COORDINATE AND 4-COORDINATE SITES

General methods are described for the synthesis of binucleating macroc yclic ligands containing 6- and 4-coordinate sites. The procedure invo lves the formation of a mononuclear complex containing two appropriate ly positioned aldehyde groups followed by acid-catalyzed condensation with a diamine to give the isolated complexes of the type [M(ligand)(H +)2]n+ where the 4-coordinate site is occupied by two protons. The fol lowing diamines were incorporated in the 6- and 4-coordinate sites; et hylenediamine, trimethylenediamine and S-1,2-propylenediamine. Eight o f the diamine combinations were isolated and characterized. The monome tallic complexes are ideal precursors for the synthesis of site-specif ic heterobimetallics under mild conditions. When S-1,2-propylenediamin e is present at the 6-coordinate site only one chiral topology is indu ced in the complex but an S-1,2-propylenediamine link at the 4-coordin ate site induces little or no diastereomeric selection. The stereochem istry of monometallic and bimetallic complexes was deduced by H-1 NMR data, X-ray crystallography, and circular dichroism spectra. The first two methods indicate that when the macrocycle contains ethylenediamin e links in both the 6- and 4-coordinate sites, the ligand cannot accom modate two metals in a planar geometry. The ideal ring size for the in corporation of two metals in a C2 symmetric topology requires trimethy lenediamine links in both sites. The circular dichroism spectra are ge nerally not useful in assigning absolute configurations without inform ation about the conformation of the ligand. The Co(III)/Co(II) redox c ouples of complexes of the type [Co(ligand)ZnCl]n+ indicate that the C o(III) state is readily accessible when the 6-coordinate site incorpor ates an ethylenediamine link but not when trimethylenediamine is prese nt at this site. It is probable that this difference reflects, in the latter complexes, the inability of the ligand to accommodate the struc tural requirements of Co(III).