COORDINATION PROPERTIES OF NITRO-SUBSTITUTED 5,15-DIPHENYL-3,7,13,17-TETRAMETHYL-2,8,12,18-TETRAETHYLPORPHYRIN WITH MANGANESE ACETATE IN PYRIDINE AND ACETIC ACID

Abstract

The synthesis of 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin and its nitro substituted was carried out. Nitro groups are located in meso-positions of the tetrapyrrole macrocycle and (or) para-positions of the phenyl rings. The synthesized porphyrins are characterized by a set of modern research methods: electron absorption spectroscopy; IR and nuclear magnetic resonance spectroscopy 1H. The reactions of the formation of manganese complexes with nitro-substituted 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin and their stability in organic solvents are studied. It was found that the rate of reactions of formation of manganese complexes in pyridine with the introduction of nitrogroups in 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphine grows as the degree of deformation of the tetrapyrrole macrocycle increases. Obviously, in this case, not only the stretching of NH bonds, due to the presence of electron-withdrawing substituents (NO2) in the para positions of the phenyl rings, makes a decisive contribution to the energy of the transition state, but also the increase in the basicity of tertiary nitrogen atoms, which form strong bonds in the transition state with a solvated cation of salt. In acetic acid, the macrocycle deformation effect leads to a decrease in the reaction rate, which is due to the specific solvation of the porphine reaction center by acetic acid molecules. It was found that steric distortions of the planar structure of porphyrins have relatively little effect on the kinetic parameters of the solvoprotolytic dissociation of manganese complexes of 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrin and its nitro-substituted ones. This is probably due to the fact that the coordination of the manganese cation results in a more planar structure of the porphyrin macrocycle. The decrease in the dissociation reaction rate with an increase in the number of nitrogroups in 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphyrine is due to the influence of the negative inductive effect of nitrogroups, which reduces the effective charge in the macrocycle on nitrogen atoms that are attacked by a solvated proton.