Synthesis and physicochemical properties of girded porphyrins

Abstract

b-Alkyl-substituted 5,15-diphenylporphyrins are synthesized, whose phenyl rings are connected through the ortho positions by bridging groups of various length. The resulting porphyrins were characterized by the electronic absorption and 1 H NMR spectra, and their structure was calculated by the molecular mechanics method. The kinetics of complex formation of the synthesized porphyrins with copper(II) acetate in acetic acid and pyridine depend on the degree of shielding of the reaction center in the tetrapyrrole ligand and its planarity.As shown in [1312], introduction into the porphyrin macroring of a great number of peripheral meso-and b-substituents or short chain of atoms, bridging separate molecular fragments, exerts a dramatic effect on the physical and chemical properties of the parent porphyrin.Proceeding with the research into the effect of the structure of porphyrin molecules on their coordination properties, we have synthesized b-octaalkyl-substituted 5,15-diphenylporphyrins I3IV whose phenyl rings are joined through the ortho positions by variouslength bridging groups.Porphyrins I3IV were prepared by trichloroacetic acid3catalyzed condensation of 2,2`-dipyrrolylmethanes with dialdehydes in acetone, followed by oxidation of the intermediate porphyrinogens with p-chloranil. The starting dialdehydes were synthesized by the reaction of salicylaldehyde with dibromides in 1-butanol in the presence of K 2 CO 3 . The porphyrins obtained were characterized by the electronic absorption and 1 H NMR spectra, and their purity and individuality were confirmed by TLC on Silufol plates (Tables 1 and 2).The geometric parameters of the synthesized porphyrins were calculated by molecular mechanics (MM+ force field). The deviations of the porphyrin macroring atoms from the mean plane drawn through the four nitrogen atoms for optimized structures I3IV corresponding to the potential energy minimum are shown in Fig. 1. It is obvious that the strong deformation of the porphyrin macroring in compounds I and II is associated with the insufficient length of the girder fragement. It should be noted that the N 4 coordination entity remains almost planar, whereas carbon atoms of the porphyrin frame deviate essentially from the mean N 4 plane, and the whole macroring assumes a dome-like shape. In porphyrins III and IV, the girder is sufficiently long and has no effect on the shape of the macroring, and the slight nonplanarity of the latter is associated with the presence of b-alkyl and meso-phenyl substituents.There is a clearly pronounced relationship between structural parameters and spectral properties of the Table 1. Yields, TLC data, and electronic absorption spectra of porphyrins I!V ÄÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Comp. ³ Yield, % ³ R f a (eluent) ³ Electronic absorption spectrum b , l max , nm (log e) no. ³ ³ ³ ÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄ I ³ 8 ³0.86 (C 6 H 6 ) ³ 639 (3.26) ³ 582 (3.64) ³ 544 (3.62) ³ 513 (3.93) ³ 41...

Pyridyl-substituted porphyrins: I. Synthesis and basicity of monopyridylporphyrins

“…The mass spectrum (electron impact, 70 eV) was obtained on an MKh-1310 instrument (ion source temperature 150-200°C). 2,2′-Methylenebis(3-ethyl-4-methyl-1H-pyrrole) (IV) was synthesized according to the procedure described in [12,13]; 3,4-dimethyl-1H-pyrrole-2-carbaldehyde (V) was prepared as reported in [14]. Organic solvents were purified by known methods [15].…”

Coordination properties of trimeric porphyrin in acetic acid

“…The rate constant of dissociation of the copper complex with the central tetrapyrrole fragment was determined using the same method as described above for the complex formation. The transformation of Cu 3 TP into (H 4 P 2+ ) 3 did not result in the change of absorbance of the solution at the stage of the Cu 2 H 2 TP complex dissociation (Fig. 2); hence, the absorbance change at that wavelength reflected the stability of the copper(II) complex with the central tetrapyrrole ring.…”

“…The earlier studies on formation and dissociation of metal complexes with mono-and dimeric porphyrins in organic solvents [1][2][3][4][5][6] have revealed that distortion of the porphyrin fragments planarity significantly affects the reactions kinetics. In extension of our studies of spatially distorted porphyrins, we have prepared the trimeric porphyrin-type ligand H 6 TP and the corresponding binuclear Сu 2 Н 2 ТР (see Scheme 1) and trinuclear Сu 3 ТР copper complexes [7].…”