Structures and properties of spatially distorted porphyrins

Electronic and steric effects of substituents on the coordinating properties of porphyrins

“…In the publications [1,3,11,14] based on calculations of the geometric parameters and on spectral data (Table 3) it was shown that porphyrins I-IV have a nonplanar structure, the degree of the macrocycle deformation increasing with the number of substituents in meso-positions. The basicity of the spatially distorted porphyrins was found to increase significantly compared with the flat analog [14].…”

“…Theoretical calculations [7][8][9] and our experimental studies [1] showed that the spectral changes of porphyrins with a sterically non-planar structures are very characteristic, so that the red shift of all bands in electron absorption spectra (EAS) of a porphyrin can be attributed to the deformation of its tetrapyrrole macrocycle with a high confidence.…”

“…The introduction of strong electron-withdrawing substituents (nitro groups) to the meso-positions of the porphyrin macrocycle was shown to change the reaction rate by an order of magnitude or less compared to the phenyl-substituted analogs. However, the introduction of a large number of bulky substituents leads to the deformation of the porphyrin ligand and thus affects much stronger the coordination properties of porphyrins, decreasing or increasing the rate of the complexation reaction by several orders of magnitude.The deformation of the porphyrin macrocycle due to the introduction of a large number of bulky substituents affects greatly the basic properties of the porphyrin ligand and, depending on the solvent nature, increases (in basic solvents) or decreases (in the solvents of acidic nature) the reaction rate of complex formation by these ligands by several orders of magnitude [1,2]. However, the substithuents themselves can more or less affect the process rate as the electron donors or acceptors.…”

“…The deformation of the porphyrin macrocycle due to the introduction of a large number of bulky substituents affects greatly the basic properties of the porphyrin ligand and, depending on the solvent nature, increases (in basic solvents) or decreases (in the solvents of acidic nature) the reaction rate of complex formation by these ligands by several orders of magnitude [1,2]. However, the substithuents themselves can more or less affect the process rate as the electron donors or acceptors.…”

Coordination and acid-base properties of meso-nitro derivatives of β-octaethylporphyrin

“…Recently, this interest has been expressed in the role of steric crowding of bulky substituents in causing nonplanar macrocyclic distortions and in the connection between tetrapyrrole conformations and their physical, chemical and coordination properties. These nonplanar conformations have been suggested to play a crucial role in the biological functions of tetrapyrroleprotein complexes [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”