Tetrapyrrole compounds macrocycle structure

Macrocyclic tetrapyrrole compounds such as heme (iron), chlorophyll (magnesium), siroheme (iron), and E12 (cobalt) contain specific metal ions at the center of their tetrapyrrole rings [17]. Metal ion chelatases can be divided into two classes based on their structural architecture. Class 1 chelatases are heteromultimeric enzymes that require three gene products for efficient catalysis [18] of the ATP-dependent chelation reaction [19]. Enzymes in this class include chlorophyll and bacteriochlorophyll magnesium chelatases [18] and aerobic cobalt chelatase (CobNST) [20]. 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

The macrocyclic tetrapyrrole structure of porphyrins was first suggested in 1912 by Kiister. At the time, Hans Fischer and others thought that such a ring was too large to be stable. Not until 1929, when Fischer and his Munich School of chemists achieved their classical total synthesis of heme, was this structure finally accepted. Fischer then went on to devise many synthetic routes to porphyrins starting from pyrroles and dipjnrrolic compounds... 

D.K.R Ng, J. Jiang, K. Kasuga and K. Machida conclude this volume with an overview of rare-earth and actinide half-sandwich tetrapyrrole complexes. When tetrapyrrole molecules, such as porphyrins or phthalocyanines, are reacted with the rare earths and actinides, they are split in half, forming the half-sandwich complexes because the metal atoms are larger than the core size of the macrocyclic ligands. They also can form sandwich-type complexes in which the metal centers are sandwiched between the macrocycles. However, this chapter is devoted to the former class of compounds. Ng and co-workers discuss the synthesis, structure, and spectroscopic and electrochemical properties of half-sandwich complexes of porphyrins and phthalocyanines. The authors... 

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