Cobalt-Containing Model Compounds

Early in the search for myoglobin or hemoglobin model compounds for study, it was learned that cobaltoheme substituted into apo—myoglobin or -hemoglobin 

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In the case of iron-containing small molecule analogs of Mb and Hb a much rockier road to successful model compounds was encountered. Even though the syntheses of iron porphyrin complexes were carried out in analogous manner to the cobalt species described above, their irreversible oxidation to the p-oxo dimer upon... 

The most direct information on the state of cobalt has come from Mossbauer spectroscopy, applied in the emission mode. As explained in Chapter 5, such experiments are done with catalysts that contain the radioactive isotope 57Co as the source and a moving single-line absorber. Great advantages of this method are that the Co-Mo catalyst can be investigated under in situ conditions and the spectrum of cobalt can be correlated to the activity of the catalyst. One needs to be careful, however, because the Mossbauer spectrum one obtains is strictly speaking not that of cobalt, but that of its decay product, iron. The safest way to go is therefore to compare the spectra of the Co-Mo catalysts with those of model compounds for which the state of cobalt is known. This was the approach taken... 

In view of the difficulties encountered using Iron(III) acetylacetonate, attention was turned to the cobalt analogue. This compound was known to show some catalytic activity. Furthermore, a simple preparative procedure Is available which seems to give a well-defined crystalline product which Is reproducible from batch to batch, both as regards appearance and catalytic ability. For this reason, a detailed Investigation of systems containing this Initiator has been undertaken as, in effect, a "model" for aqueous-phase diene polymerisations using this class of Initiator. 

A number of papers have been concerned with substitution reactions of Vitamin B12 model compounds. Kinetics of the substitution of the alkylaquo-l,3-bis(acetyl monoximeimino)propanato-cobalt ions (MH2O) by L are consistent with formation of an intermediate MH20,L only when L contains an aromatic group. Sjxl substitution reactions of the axial aquo-ligand in methyl aquo-cobaloxime by thiols, primary amines, and 4-substituted pyridines have been described. 

Additionally to nickel ICC, chelates of the types 467, 468, 472, and 473, containing either cobalt, iron, copper, palladium, zinc, cadmium, or mercury, have also been obtained [269,270,804]. Special interest amongst them is provoked by copper ICC containing an azomethinic N,S-ligand environment. These compounds are one of the several biomimetic models of nonporphyrine metal proteins [448,804,834]. The majority of these ICC have trimetallocyclic structures of the types shown by struc-... 

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