Cobalt(III) complexes of bidentate azotyrosine analogs.

As analogs for cobalt(III) complexes of bidentate azotyrosine in proteins, several cobalt(III) complexes of bidentate azophenols have been prepared and characterized. Tris(2-phenylazo-p-cresolato)cobalt(III) was shown to be a poor model complex for this purpose; while cobalt(III) complexes of either 2-phenylazo-p-cresol or 2-(4-carboxyphenylazo)-4,5-dimethylphenol with the linear tetradentate ligand ethylenediamine-N,N'-diacetic acid are very useful as model complexes. The complexes were characterized by magnetic susceptibility, visible spectra and 1H NMR. In the case of one of the mixed ligand complexes, a detailed description of the stereochemistry was possible. Comparisons of the spectral characteristics of metal complexes with bidentate and tridentate azophenols are made. These model studies are essential to a program involving the site specific modification of proteins with substitution inert metal ions.