TRANSITION METAL COMPLEXES OF PORPHINS, CORRINS AND RELATED COMPOUNDS

The group of macrocyclic tetrapyrrolic ligands which includes the porphins, chlorins and corrins, occur in several biologicafly important molecules in the form of metal complexes. Intermediate in structure between the porphins and the corrins are the corroles and the 1-monosubstituted-, and 1,1 9-disubstituted tetradehydrocorrins. Syntheses and reactions of metal, particularly nickel, complexes of these novel ring systems are described. The vitamin B12 coenzyme, which is a cobalt—corrin derivative containing adenosine bound to the cobalt through a 5'-carbon--cobalt covalent bond, is considered in the light of this unique structural feature. The mode of bio-synthesis of the coenzyme can be partially simulated in the laboratory and a brief survey of the biochemical reactions controlled by the coenzyme is given. The recognition of the structures of the vital transition metal complexes haemin(I) and chlorophyll(II)1 gave an important biological impetus to organometallic chemistry in its very early days, and at the same time initiate