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Synthesis and Spectral Properties of ms-Tetrasubstituted b-Octaalkylporphyrins

Institute of the Solution Chemistry of Russian Academy of Sciences, 153045, Akademicheskaya, 1, Ivanovo, Russian Federation
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Molecules 2000, 5(6), 757-761; https://doi.org/10.3390/50600757
Received: 7 March 2000 / Accepted: 27 March 2000 / Published: 8 June 2000
(This article belongs to the Special Issue Porphyrin Chemistry)

Abstract

Four new ms-tetrasubstituted β-octaalkylporphyrins are synthesized and their spectral properties are discussed.
Keywords: Porphyrin; dipyrrolylmethane; ms-substitution Porphyrin; dipyrrolylmethane; ms-substitution

Introduction

Porphyrin synthesis variants are diverse, and the choice of a particular strategy is usually determined by the nature and relative position of the substituents desired in a given molecule. Simple porphyrins with identical substituents in ms- or β-positions are usually prepared by methods based on monopyrrole condensation, when four identical pyrrole molecules are condensed into a porphyrin in one step. More complicated structures are prepared through intermediate di- or tetrapyrrole compounds, in which the presence of the substituents leads to the possibility of formation of isomers around a substituent posi-tion. In the present work a method for synthesis of new ms-tetrasubstituted β-octaalkylporphyrins is reported. The advantage of the given method is that after condensation, not even insignificant amounts of isomeric porphyrins are detectable in the reaction mixture.

Results and Discussion

Condensation of ms-arylsubstituted dipyrrolylmethanes 1-3 [1] with aldehydes RCHO (R = CH3, C4H9) gives 5,15-diphenyl-3,7,10,13,17,20-hexamethyl-2,8,12,18-tetrabutylporphyrin (4), 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,10,12,18,20-hexabutylporphyrin (5), 5,15-di-(4-methoxyphenyl)- 3,7,13,17-tetramethyl-2,8,10,12,18,20-hexabutylporphyrin (6) and 5,15-di-(4-nitrophenyl)-3,7,13,17- tetramethyl-2,8,10,12,18,20-hexabutylporphyrin (7) (cf. Scheme 1).
The reactions of 5,5'-dicarboxydipyrrolylmethanes (1-3) with appropriate aldehydes was carried out in pyridine at elevated temperatures and pressures. Maximum yields were obtained by the reaction of 1 mole ms-phenyl-5,5'-dicarboxy-4,4'-dibutyl-3,3'-dimethyl-2,2'-dipyrrolylmethane (1) with 3.6 moles of aldehyde in the presence of 3.6 moles of nitrobenzene. The increased yield observed in the presence of nitrobenzene is probably related to the oxidizing ability of nitro-group. The rather low yields of ms- tetrasubstituted porphyrins (4-7) is probably caused by unfavourable spatial factors affecting the cyclo-condensation process. Similar results were obtained for condensation of 2,5-unsubstituted 3,4-dimethyl-pyrroles with aldehydes [2]. The porphyrin yield was 5-6% and did not depend on the nature of the al-dehyde.
1H-NMR-spectra are in complete accord with the proposed structures 4-7. The signals of the ms-phenyl group protons appear in the range of 7.7-8.0 ppm. The chemical shifts of the β-alkyl protons are located between 0,8-4,0 ppm. The magnetic field of the porphyrin ring π-electron current influences the position of signals of the hydrocarbon fragments of the ms-substituents, a fact reflected in the NMR spectrum by the separate, non-overlapping, signals of the CH2 and CH3 fragments of the alkyl substitu-ents. Thus, in porphyrins 5-7 the protons of the CH2 groups of the butyl substituents directly connected to the macroheterocyle appear as a triplet at 4.5 ppm., the adjacent CH2 group gives a pentet at 2.5 ppm., the following CH2 group gives a sextet located at 1.55 ppm. Finally, the terminal CH3 group ap-pears as a triplet at 0.85 ppm. Substitution in the phenyl rings of 5,15-diphenylporphyrins (X = 4-OCH3 in compound 6, 4-NO2 in 7) has no significant effects on the position of β-alkyl and ms-substituent proton signals. The disappearance of N-H proton bands is unclear. Similar effects have been observed for ms-tetraphenylsubstituted β-octamethylporphyrin [3].
ms-Tetrasubstituted octaalkylporphyrins 4-7 have a deformed porphyrin cycle structure, that causes a red shift and broadening of the absorption in the UV-vis. spectra in a comparison with tetraphenylpor-phyrin and ms-unsubstituted octaalkylporphyrins [3]. To confirm the molecular structures the IR spectra of the synthesized porphyrins were investigated. Together with the NMR data they reliably prove the proposed structures 4-7 in most cases.

Experimental

General

1H NMR spectra were recorded on a Bruker AC-500 spectrometer operating at 600 MHz with HMDS as internal standard in CDCl3. UV-vis. spectra were obtained on a Specord M400 spectropho-tometer in CHCl3. IR spectra (KBr disks) were obtained on a Specord M80 spectrophotometer.

5,15-Diphenyl-3,7,10,13,17,20-hexamethyl-2,8,12,18-tetrabutylporphyrin (4)

A mixture of ms-phenyl-5,5/-dicarboxy-4,4/-dibutyl-3,3/-dimethyl-2,2/-dipyrrolylmethane (1, 0.50 g), anhydrous zinc acetate (0.63 g), nitrobenzene (0.48 mL), pyridine (8 mL) and acetaldehyde (0.20 mL) was heated at 180° C for 2 hours in a sealed ampule. The reaction mixture was cooled, diluted with water (50 mL) and heated at 100° for 30 minutes. The precipitate was isolated by filtration and kept into a solution of sulfuric acid (0.50 mL) in dimethylformamide (50 mL) for 1 hour. The product was extracted with 50 mL of chloroform and washed with water, then ammonia solution and water again. The product was purified by silica gel chromatography (benzene), followed by recrystallization (CHCl3/methanol) to afford the title compound. Yield 32 mg (8%). Rf 0.30 (Silufol, benzene); UV-vis (CHCl3): λmax, nm (lg ε) 629.1(3.48); 547.5(3.62); 540.4(3.68); 507.1(4.01); 421.4(4.89). IR , cm-1: νNH 3325; δNH 974; γNH 710; νCH 3060; δCH 1500. 1H NMR (CDCl3): phenyl protons - [7.97d (4H; o-H); 7.35 t (4H; m-H); 7.70 t (2H; p-H)]; 4.00 s (6H; ms-CH3); 3.92 (t, 8H, CH2CH2CH2CH3); 2,42 s (12H; β-CH3); 2.13 (pentet, 8H, CH2CH2CH2CH3), 1.64 (sextet, 8H, CH2CH2CH2CH3), 1.11 (t, 12H, CH2CH2CH2CH3). Anal. Calcd for C57H84N4: C 83.01, H 10.19, N 6.80. Found: C 82.98, H 10.14, N 6.77.
The following substances were similarly prepared:

5,15-Diphenyl-3,7,13,17-tetramethyl-2,8,10,12,18,20-hexabutylporphyrin (5)

Yield 37,7 mg (9.5%). Rf 0.39 (Silufol, benzene); UV-vis (CHCl3): λmax, nm (lg ε) 629.9 (3.50); 548.1 (3.67); 540.9 (3.70); 507.7 (4.08); 422.1 (4.90). IR, cm-1: νNH 3322; δNH 971; γNH 712; νCH 3067; δCH 1505. 1H NMR (CDCl3): phenyl protons: 7.92d (4H; o-H); 7.37 t (4H; m-H); 7.68 t (2H; p-H)]; 4.50 t (4H; ms-CH2CH2CH2CH3); 4.07 s (6H; ms-CH3); 3.90 (t, 8H, CH2CH2CH2CH3); 2.50 pentet (4H; ms-CH2CH2CH2CH3); 2.42 s (12H; β-CH3); 2.10 (pentet, 8H, CH2CH2CH2CH3); 1.62 (sextet, 8H, CH2CH2CH2CH3); 1.55 sextet (4H; ms-CH2CH2CH2CH3); 1.08 (t, 12H, CH2CH2CH2CH3); 0.85 t (6H; ms-CH2CH2CH2CH3). Anal. Calcd for C63H96N4: C 83.26, H 10.57, N 6.17. Found: C 83.21, H 10.52, N 6.12.

5,15-Di-(4-methoxyphenyl)-3,7,13,17-tetramethyl-2,8,10,12,18,20-hexabutylporphyrin (6)

Yield 39 mg (10%). Rf 0.47 (Silufol, benzene); UV-vis (CHCl3): λmax, nm (lg ε) 626.8 (3.43); 548.9 (3.61); 542.3 (3.78); 508.7 (4.11); 425.1(4.99). IR, cm-1: νNH 3326; δNH 978; γNH 717; νCH 3072; δCH 1510. 1H NMR (CDCl3): phenyl protons: 7,90 d (4H; o-H); 7,33 t (4H; m-H); 4,52 t (4H; ms- CH2CH2CH2CH3); 4,11 s (6H; ms-CH3); 4.00c(6H; CH3O); 3.90 (t, 8H, CH2CH2CH2CH3); 2.55 pentet (4H; ms-CH2CH2CH2CH3); 2.40 s (12H; β-CH3); 2.16 (pentet, 8H, CH2CH2CH2CH3); 1.69 (sextet, 8H, CH2CH2CH2CH3); 1.53 sextet (4H; ms-CH2CH2CH2CH3); 1.12 (t, 12H, CH2CH2CH2CH3); 0.80 t (6H; ms-CH2CH2CH2CH3). Anal. Calcd for C65H100N4O2: C 80.58, H 10.33, N 5.78. Found: C 80.52, H 10.30, N 5.72.

5,15-Di-(4-nitrophenyl)-3,7,13,17-tetramethyl-2,8,10,12,18,20-hexabutylporphyrin (7)

Yield 40 mg (10%). Rf 0.17 (Silufol, benzene); UV-vis (CHCl3): λmax, nm (lg ε) 631.1(3.53); 549.2(3.71); 541.2 (3.71); 508.7(4.11); 424.7(4.94). IR (KBr), cm-1: νNH 3328; δNH 976; γNH 723; νCH 3070; δCH 1511. 1H NMR (CDCl3): phenyl protons: 7.92d (4H; o-H); 7,37 t (4H; m-H)]; 4.50 t (4H; ms-CH2CH2CH2CH3); 4.07 s (6H; ms-CH3); 3.90 (t, 8H, CH2CH2CH2CH3); 2.50 pentet (4H; ms- CH2CH2CH2CH3); 2.42 s (12H; β-CH3); 2.10 (pentet, 8H, CH2CH2CH2CH3); 1.62 (sextet, 8H, CH2CH2CH2CH3); 1.55 sextet (4H; ms-CH2CH2CH2CH3); 1.08 (t, 12H, CH2CH2CH2CH3); 0.85 t (6H; ms-CH2CH2CH2CH3). Anal. Calcd for C63H94N6O4: C 75.75, H 9.42, N 8.42. Found: C 75.72, H 9.38, N 8.37.

References and Notes

  1. Mamardashvili, N. Zh.; Zdanovich, S. A.; Golubchikov, O. A. Synthesis and spectral properties of dipyrrolylmethanes. Russian J. Org. Chem. 1998, 34, 1234–1239. [Google Scholar]
  2. Manka, J. S.; Lavrens, D. S. Self-assembly of a hydrophobic groove. Tetrahedron Lett. 1989, 30, 7341–7344. [Google Scholar] [CrossRef]
  3. Semeykin, A. S. Synthesis of ms-substituted porphyrins. Advances in Porphyrin Chemistry V.1. SPb.: The Scientific Research Institute of Chemistry, St.-Petersburg University. 1997, 52–66. [Google Scholar]
  • Samples Availability: Available from the authors.
Scheme 1.  
Scheme 1.  
Molecules 05 00757 sch001
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