Magnesium dihydroporphyrin complexes

Chlorophyll. A green photosynthetic pigment that is made of a magnesium dihydroporphyrin complex. 

Chlorins (2) are undoubtedly the most important dihydroporphyrins, since the chlorin chromophore is found in chlorophylls and some bacteriochlorophylls and, as the magnesium complex, is the catalyst in photosynthesis. The method of choice for formation of trans-chlorins involves reduction of iron porphyrins with sodium in boiling isopentyl alcohol (57JCS3461), but methods involving photochemical reduction of tin(IV) porphyrins, isomerization of phlorins, reduction of metalloporphyrins with sodium anthracenide followed by protonolysis, heating with sodium ethoxide, and photoreductions of zinc(II) porphyrins in the presence of ascorbic acid have also been employed. The best method for formation of c/s-chlorins (note that all natural chlorophylls possess the trans arrangement) appears to... 

Chlorophyll a with a Q -band at Amax = 665nm (95) is the magnesium complex of the dihydroporphyrin derivative 3 already shown in Fig. 3. The chemically quite different structures of compounds 7 and 8 are given in Fig. 9. 

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