BIMETALLIC REACTIVITY - PREPARATION AND CHARACTERIZATION OF SYMMETRICAL BIMETALLIC COMPLEXES OF A BINUCLEATING MACROCYCLIC LIGAND, CYTIM, CONTAINING 6-COORDINATE AND 4-COORDINATE SITES

A binucleating macrocylic ligand, cytim, incorporating 6- and 4-coordinate sites has been prepared. The two metals are bridged by phenolic oxygen ligands, and the 4-coordinate site is completed by a trimethylenediimine link. The 6-coordinate site carries two 2-methylenepyridyl arms and is completed by a trimethylenediamine chelate. This ligand was constructed in order to determine whether the trimethylenediamine chelate in the 6-coordinate site would produce symmetrical complexes where the pyridine ligands lie trans above and below the mean molecular plane. Previous work had shown that the analogous ligand with an ethylenediamine link in this site gave unsymmetrical bimetallic complexes where the pyridines were cis on one side of the mean macrocylic plane. Synthetic methods for preparing the monometallic complexes, [M(cytim)(H+)2]2+ (M = Zn(II),Co(II)), are described. These complexes provide mild methods for introducing a second metal into the 4-coordinate site which is occupied by two protons in the monometallic complexes. The, H-1 NMR spectra of the diamagnetic complexes and X-my crystal structures of [Zn(cytim)(H+)2](PF6)2 and of [Zn(cytim)Zn(OAc)]PF6 demonstrate that the expected trans pyridine symmetric structures are formed. That macrocylic formation is necessary for obtaining symmetrical structures was demonstrated by the fact that complexes of analogous non-macrocylic ligands give all possible topological octahedral isomers. Magnetic moments, electronic absorption spectra, and redox couples are reported. Perhaps, the most significant observation was that Co(III) in the 6-coordinate site of cytim is unstable. This is attributed to the inability of cytim to adjust to the Co(III) bond lengths.