Crystal and molecular structures of some mono-meso-substituted free base and zinc(II)octaalkylporphyrins

Studies on highly substituted porphyrins bearing eight β-substituents and at least one bulky mesosubstitutent have shown that peripheral steric strain leads to considerable macrocycle distortion. While this is well established for porphyrins with dodecasubstitution ; the situation is less clear for nonasubstituted porphyrins with meso-substituents such as methyl, aryl or ester groups. In order to further study this situation we have investigated the conformation of nonasubstituted porphyrins with small meso-substitutents by determination of the crystal structures of : 2,3,7,8,12,13,17,18-octaethyl-5-(N-succinimidyl)porphyrin, 1 ; 2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-5-methoxymethylporphyrin, 2 ; pyridine(2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-5-methoxymethylporphyrinato) zinc(II), 3 ; methanol(5-acetoxy-2,7,12,17-tetraethyl-3,8,13,18-tetramethyl-porphyrinato) zinc(II) methanol solvate, 4 ; and (2,3,7,8,12,13,17,18-octaethyl-5-methylporphyrinato)zinc(II), 5. The compounds show only small deviations from planarity which might be due to packing effects, however, all compounds show some degree of rhomboic elongation of the porphyrin core.