Macrocyclic ligands chlorin

In such a large subject, this article can only focus on certain aspects, namely those that involve complexation with inorganic substrates. We only consider the synthetic macrocycles, with emphasis on transition metal complexation. Aza, oxa, and, to a lesser extent, thia and phospha macrocycles are also covered. The naturally occurring porphyrins, corrins, corphins, chlorins, and phthalocyanins, as well as the cyclodextrins, are not included. Because of the general complexity of macrocyclic systems and the resulting complicated systematic names, commonly used abbreviations or simplified names will be employed. This review will encompass the synthesis, thermodynamics, structure, and applications of macrocyclic ligands. 

By far the most well known and chemically facile reaction of the porphyrin and chlorin macrocycles is chelation. The porphyrin core is a perfect ligand for a whole host of ions, complexes with most metals in the periodic chart having been prepared and characterized. 

Fe3+ derivatives of porphyrins and chlorins are all high spin in the absence of N-donor axial ligands and in chlorinated solvents [41,42] the low spin state observed in the case of iron corrolate demonstrates that the ligand field strength of corrole is very different from that of other macrocycles. 

Hambley et al. have also predicted isomer distributions of chlorocobalt(IIl) complexes of pendant-arm macrocycles.The force field used had been detailed earlier. Of the ligands studied (12-methyl-l,4,7,10-tetraazacyclotridecan-12-amine, 6-methyl-l,4,8,1 l-tetraazacyclotetradecan-6-amine, lO-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine, and 3-methyl-l,5,9,13-tetraazacyclohexa-decan-3-amine), the cis isomer (the pendant primary amine is coordinated cis to the chlorine) was found to be the lowest energy form in each case. For 6-methyl-1,4,8,ll-tetraazacyclotetradecan-6-amine, the cis isomer was 4.4 kj/mol more stable than trans (cis/trans = 86 14). The calculated ratio was in reasonable agreement with experiment (cis/trans = 98 2). 

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