Synthesis and characterization of a new dioxime and its cobalt(III) complexes as vitamin B12 models

A new dioxime ligand abbreviated as H2L, 2',3',3,8-tetramethyl-5,6-benzo-4,7-diazadeca-3,7-diene-2,9-dione dioxime, has been synthesized by the condensation reaction of 4,5-dimethyl-2,3-diamino benzene with diacetyl monoxime. The ligand provides a deep cleft within which axial ligands such as pseudo-halogens and Lewis base coordinate. The dibromo complex of this ligand [Co(HL)Br-2] (3) has been prepared by the reaction of H2L with cobalt(II) bromide hexahydrate. This complex has been employed as a starting material for further substitution reactions. Octahedral cobalt (III) complexes containing a benzyl group as axial ligand have also been prepared by reacting (3) with benzyl chloride and pyridine or substituted pyridine. The structures of the dioxime and its complexes are proposed on the basis of elemental analyses, H-1 and C-13 NMR, IR and MS spectral data.