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-coordi nate sites has been prepared. The two metals are bridged by phenolic o xygen ligands, and the 4-coordinate site is completed by a trimethylen ediimine link. The 6-coordinate site carries two 2-methylenepyridyl ar ms and is completed by a trimethylenediamine chelate. This ligand was constructed in order to determine whether the trimethylenediamine chel ate in the 6-coordinate site would produce symmetrical complexes where the pyridine ligands lie trans above and below the mean molecular pla ne. Previous work had shown that the analogous ligand with an ethylene diamine link in this site gave unsymmetrical bimetallic complexes wher e the pyridines were cis on one side of the mean macrocylic plane. Syn thetic 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 whic h is occupied by two protons in the monometallic complexes. The, H-1 N MR 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 macr ocylic formation is necessary for obtaining symmetrical structures was demonstrated by the fact that complexes of analogous non-macrocylic l igands give all possible topological octahedral isomers. Magnetic mome nts, electronic absorption spectra, and redox couples are reported. Pe rhaps, the most significant observation was that Co(III) in the 6-coor dinate site of cytim is unstable. This is attributed to the inability of cytim to adjust to the Co(III) bond lengths.