Abstract
Complex formation of four atropisomers of zinc tetra(ο-pivalamidophenyl)porphyrin with imidazoles (imidazole, 1-methylimidazole, 2-methylimidazole, and benzimidazole) and pyridines (pyridine, 3, 5-dimethylpyridine, and 2, 6-dimethylpyridine) was studied. The ratios of the absorbance of the βband to the αband in the adducts tended to be in the order of αααα>ααββ≥αααβ>αβαβ. This order, which is the same as that of "electronic effect" on the physical properties of the four atropisomers of tetra(ο-pivalamidophenyl)porphyrin, indicates the presence of "electronic effect" in the zinc derivatives of the porphyrin. Among the four isomers, the equilibrium constants of N-base binding tended to be in the order of αβαβ>αααα≥αααβ>ααββ, suggesting the relatively greater importance of "steric effect" of the bulky pivalamido groups rather than "electronic effect" for the coordination of the N-bases. The differences in the equilibrium constants among the atropisomers are attributable to the contributions of both the steric effect and the electronic effect.
