Fluoroalkylation of Porphyrins: Generation of 2- and 20-Perfluoroalkyl-5,10,15-triarylporphyrin Radicals and their Intramolecular Cyclizations

Liang Chen; Li-Mei Jin; Can-Cheng Guo; Qing-Yun Chen

doi:10.1055/s-2005-864833

LETTER

Fluoroalkylation of Porphyrins: Generation of 2- and 20-Perfluoroalkyl-5,10,15-triarylporphyrin Radicals and their Intramolecular Cyclizations

Liang Chen^a, Li-Mei Jin^b, Can-Cheng Guo*^a, Qing-Yun Chen*^a,b
^a College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082, P. R. China
e-Mail: ccguo@mail.hunu.edu.cn;
^b Key laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, P. R. China
Fax: +86(21)64166128; e-Mail: chenqy@mail.sioc.ac.cn;

Abstract

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Abstract

Treatment of 5,10,15-triarylporphyrin (1) with perfluoroalkyl iodides (RfI,2) in the presence of Na₂S₂O₄/NaHCO₃ in DMSO-CH₂Cl₂ at 65 °C for 3 hours gave a mixture of 2-polyfluoroalkyl-5,10,15-triarylporphyrins 3 and 5,10,15-triaryl-20-polyfluoroalkylporphyrins 4. When 1,3-diiodohexafluoropropane (2e) was reacted under the same conditions for 8 hours, the products were 5,10,15-triaryl-2,20-(hexafluoropropanediyl)porphyrins 5. Both 3e and 4e afforded the same compounds 5 at 65 °C after a reaction time of 6 hours. Either 2-(2-chlorotetrafluoroethyl)-5,10,15-triphenylporphinato zinc(II) (Zn3aa) or 5,10,15-triphenyl-20-(2-chlorotetrafluoroethyl)porphinato zinc(II) (Zn4aa) resulted in 5,10,15-triaryl-2,20-(tetrafluoroethanediyl)porphinato zinc(II) (Zn7) in excess Na₂S₂O₄/NaHCO₃ in DMSO-CH₂Cl₂ at 100 °C after 3 hours. Both Zn5a and Zn7 can be hydrolyzed quantitatively to 5,10,15-triaryl-2,20-(20′-oxo)(tetrafluoropropanediyl)porphinato zinc(II) (Zn8) and 5,10,15-triphenyl-2,20-(20′-oxo)(difluoroethanediyl)porphinato zinc(II) (Zn9), respectively in the presence of silica gel at room temperature.

Key words

fluoroalkylation - intramolecular cyclizations - porphyrins - perfluoroalkyl iodides

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References

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General Procedure for the Preparation of 2-Polyfluoroalkyl-5,10,15-triarylporphyrins ( 3) and 5,10,15-Triaryl-20-polyfluoroalkylporphyrins(4) Porphyrin 1 (0.2 mmol)was dissolved in a mixture of DMSO-CH₂Cl₂ (1:1, 60 mL), then RfI (0.6 mmol), Na₂S₂O₄ (0.9 mmol), and NaHCO₃ (0.9 mmol) were added in the order given. The mixture was stirred for 3 h at 65 °C. The progress of the reaction was monitored by TLC. When most of the starting material was consumed, the mixture was washed with water several times. The organic layer was dried over anhydrous Na₂SO₄ and concentrated on a rotary evaporator. The crude products were purified by dry column chromatography (hexane-CH₂Cl₂, 2:1). The first red-purple band was removed and washed with CH₂Cl₂, to give a mixture of 3, 4, (15-30%; 3aa, 4aa 28%; 3ab, 4ab 30%; 3ac, 4ac 25%; 3ad, 4ad 30%; 3ae, 4ae 30%; 3be, 4be 15%; 3ce, 4ce 28%). The second dark-purple band was unconsumed starting material. The red-purple band was further purified by flash chromatography [300-400 mesh silica gel, petroleum ether-CH₂Cl₂ (3:1)] to yield a light purple solid.
General Procedure for Metalation of 3 and 4 A mixture of 3, 4 (40 mg)and Zn(OAc)₂·2H₂O (5 equiv) were placed in a round-bottomed flask, then a mixture of CH₂Cl₂ (25 mL) and MeOH (3 mL) was added. The mixture was stirred at r.t. for 1 h, and then washed with water several times. The organic layer was dried over anhydrous Na₂SO₄ and concentrated on a rotary evaporator to dryness. The residue was subjected to flash chromatography [silica, petroleum ether-CH₂Cl₂ (2:1)] to yield two fractions. The front running red-blue band afforded on evaporation 2-polyfluoroalkyl-5,10,15-triarylporphinato zinc(II) (Zn3) (25-30%). The second red-purple band yielded on evaporation 5,10,15-triaryl-20-polyfluoroalkylporphinato zinc(II) (Zn4) (65-70%).
2-(2-Chlorotetrafluoroethyl)-5,10,15-triphenyl-porphinato zinc(II) (Zn3aa)
¹H NMR (300 MHz, CDCl₃): δ (ppm) = 7.76-7.83 (m, 9 H), 8.19-8.25 (m, 6 H), 8.95-8.99 (m, 4 H), 9.28 (AB, J = 55.0 Hz, 2 H), 9.38 (s, 1 H), 10.49 (s, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -68.62 (s, 2 F), -99.73 (s, 2 F). UV-vis:
λ_max (relative intensity, CH₂Cl₂) = 581 (1.0), 546 (3.2), 416 (88.2). MS (MALDI): m/z = 734 (M⁺). HRMS (MALDI): m/z calcd for C₄₀H₂₃ClF₄N₄Zn⁺, 734.0839; found, 734.0833.
5,10,15-Triphenyl-20-(2-Chlorotetrafluoro-ethyl)porphinato Zinc(II) (Zn4aa)
¹H NMR (300 MHz, CDCl₃): d (ppm) = 7.73-7.81 (m, 9 H), 8.19 (d, J = 3.2 Hz, 6 H), 8.90 (AB, J = 12.3 Hz, 4 H), 9.04 (d, J = 2.4 Hz), 9.63 (s, 2 H). ¹⁹F NMR (282 MHz, CDCl₃): d (ppm) = -63.48 (s, 2 F), -75.06 (s, 2 F). UV-vis: l_max (relative intensity, CH₂Cl₂) = 580 (1.0), 547 (2.2), 416 (56.4). MS (MALDI): m/z = 734 (M⁺). HRMS (MALDI): m/z calcd for C₄₀H₂₃ClF₄N₄Zn⁺, 734.0839; found, 734.0833.
Demetalation of Zn3 or Zn4 A sample of Zn3 or Zn4 (20 mg)was dissolved in CH₂Cl₂ (30 mL) and treated with concentrated sulfuric acid (several drops) for 5 min. The organic layer was washed with water several times and dried over anhydrous sodium sulfate. After evaporation of the solvent, a purple solid 2-polyfluoroalkyl-5,10,15-triarylporphyrins (3) or 5,10,15-triaryl-20-poly-fluoroalkylporphyrins (4) was obtained in 90% yield.
2-(2-Chlorotetrafluoroethyl)-5,10,15-triphenyl-porphyrin ( 3aa)
¹H NMR (300 MHz, CDCl₃): δ (ppm) = -2.96 (s, 2 H), 7.75-7.86 (m, 9 H), 8.21-8.27 (m, 6 H), 8.81-8.86 (m, 2 H), 8.98 (AB, J = 6.9 Hz, 2 H), 9.29 (s, 1 H), 9.31 (AB, J = 58.4 Hz, 2 H), 10.48 (s, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -68.58 (s, 2 F), -99.76 (s, 2 F). UV-vis: λ_max (relative intensity, CH₂Cl₂) = 643 (1.4), 588 (1.2), 546 (1.0), 513 (4.2), 415 (95.4). MS (ESI): m/z = 673 (MH⁺). Anal. Calcd for C₄₀H₂₅ClF₄N₄·3H₂O: C, 66.07; H, 4.30; N, 7.71. Found: C, 66.30; H, 4.54; N, 7.22.
5,10,15-triphenyl-20-(2-Chlorotetrafluoro-ethyl)porphyrin ( 4aa):
¹H NMR (300 MHz, CDCl₃): δ (ppm) = -2.47 (d, J = 17.4 Hz, 2 H), 7.73-7.83 (m, 9 H), 8.18 (d, J = 3 Hz, 6 H), 8.78 (AB, J = 13.9 Hz, 4 H), 8.92 (d, J = 2.4 Hz, 2 H), 9.47 (s, 2 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -63.87 (s, 2 F), -77.93 (s, 2 F). UV-vis: λ_max (relative intensity, CH₂Cl₂) = 640 (1.0), 584 (1.4), 549 (1.7), 512 (3.5), 415 (61.0). MS (MALDI): m/z = 673 (MH⁺). HRMS (MALDI): m/z calcd for C₄₀H₂₅ClF₄N₄·H⁺: 673.1782; found: 673.1777.

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General Procedure for the Preparation of 5,10,15-Triaryl-2,20-(hexafluoropropanediyl)porphyrins ( 5) The porphyrin (0.2 mmol)was dissolved in DMSO-CH₂Cl₂ (1:1, 60 mL), then ICF₂CF₂CF₂I (0.3 mmol), Na₂S₂O₄ (0.9 mmol), and NaHCO₃ (0.9 mmol) was added in the order given. The mixture was stirred for 8 h at 65 °C. The progress of the reaction was monitored by TLC. Then CH₂Cl₂ (30 mL) was added and the resulting solution was washed with water thrice. The organic layer was dried over anhydrous Na₂SO₄ and evaporated to dryness. The crude products were purified by dry column chromatography, [petroleum ether-CH₂Cl₂ (3:1)]. The first red-purple band was dug out and washed with CH₂Cl₂ to give 5 (5a 30%, 5b 15%, 5c 18%). The red-purple band was further purified by flash chromatography [300-400 mesh silica gel, petroleum ether-CH₂Cl₂, (4:1)] to yield a light purple solid. 5,10,15-Triphenyl-2,20-(hexafluoropropane-diyl)porphyrins ( 5a) ¹H NMR (300 MHz, CDCl₃): δ (ppm) = -2.74 (s, 2 H), 7.77-7.89 (m, 9 H), 8.21-8.26 (m, 6 H), 8.79 (AB, J = 6.3 Hz, 2 H), 9.00 (s, 2 H), 9.17 (d, J = 2.7 Hz, 1 H), 9.41 (s, 1 H), 9.91 (d, J = 2.1 Hz, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -81.96 (s, 2 F), -104.34 (s, 2 F), -131.21 (s, 2 F). UV-vis: λ_max (relative intensity, CH₂Cl₂) = 639 (1.0), 585 (1.3), 519 (3.2), 418 (73.8). MS (MALDI): m/z = 687 (MH⁺). HRMS (MALDI): m/z calcd for C₄₁H₂₄F₆N₄·H⁺: 687.1983; found: 687.1978.
General Procedure for the Metalation of 5,10,15-Triaryl-2,20-(hexafluoropropanediyl)porphyrins ( 5) A sample of porphyrin (20 mg) and Zn(OAc)₂·2H₂O (5 equiv) was placed in around-bottomed flask, then CH₂Cl₂ (25 mL) and MeOH (3 mL) was added. The mixture was stirred at r.t. for 1 h. Then the mixture was washed with water several times. The organic layer was dried over anhydrous Na₂SO₄ and concentrated to dryness on a rotary evaporator to Zn5.
5,10,15-Triphenyl-2,20-(hexafluoropropane-diyl)porphinato Zinc(II) (Zn5a) ¹H NMR (300 MHz, CDCl₃): δ (ppm)= 7.73-7.88 (m, 9 H), 8.17-8.23 (m, 6 H), 8.92-8.98 (m, 4 H), 9.11 (d, J = 2.7 Hz, 1 H), 9.49 (t, J = 2.4 Hz, 1 H), 9.86 (AB, J = 4.2 Hz, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -81.99 (s, 2 F), -104.21 (s, 2 F), -131.51 (s, 2 F). UV-vis: λ_max (relative intensity, CH₂Cl₂) = 596 (1.0), 562 (2.0), 429 (49.3). MS (MALDI): m/z = 748 (M⁺). HRMS (MALDI): m/z calcd for C₄₁H₂₂F₆N₄Zn⁺: 748.1040; found: 748.1035.

General Procedure for the Preparation of 5,10,15-Triaryl-2,20-(tetrafluoroethanediyl)porphinato Zinc(II) (Zn7a) A sample of porphyrin (0.1 mmol)was dissolved in DMSO (20 mL), then Na₂S₂O₄ (1 mmol) and NaHCO₃ (1 mmol) were added in the order given. The mixture was stirred for 3 h at 100 °C. The course of the reaction was monitored by TLC. After addition of CH₂Cl₂ (40 mL), the mixture was washed with water several times. The organic layer was dried over anhydrous Na₂SO₄ and evaporated to dryness. The crude products were purified by flash chromatography [300-400 mesh silica gel, petroleum ether-CH₂Cl₂ (1:1 v/v)] to yield Zn7a (40%) as a light purple solid.
5,10,15-Triaryl-2,20-(tetrafluoroethanediyl)porphinato zinc (II) (Zn7)
¹H NMR (300 MHz, CDCl₃): δ (ppm)= 7.68-7.75 (m, 9 H), 8.12-8.20 (m, 6 H), 8.92 (AB, J = 24 Hz, 2 H), 8.93 (s, 2 H), 9.07 (d, J = 2.3 Hz, 1 H), 9.17 (s, 1 H), 9.55 (d, J = 2.3 Hz, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -81.64 (s, 2 F), -97.48 (s, 2 F). UV-vis: λ_max (relative intensity, CH₂Cl₂) = 562 (1.0), 427 (30.3). MS (MALDI): m/z = 698 (M⁺). HRMS (MALDI): m/z calcd for C₄₀H₂₂F₄N₄Zn⁺: 698.1072; found: 698.1067.
Demetalation of 5,10,15-Triaryl-2,20-(tetrafluoroethanediyl)porphinato Zinc(II) (Zn7a) A sample of Zn7a (20 mg)was dissolved in CH₂Cl₂ (30 mL) and treated with concentrated sulfuric acid (several drops) over 5 min. The organic layer was washed with water several times and dried over anhydrous sodium sulfate. After evaporation of the solvent, 7a (90%) was obtained as a purple solid.
5,10,15-Triphenyl-2,20-(tetrafluoroethane-diyl)porphyrins ( 7a) ¹H NMR (300 MHz, CDCl₃): δ (ppm) = -2.59 (d, J = 159.2 Hz, 1 H), 7.73-7.85 (m, 9 H), 8.19-8.30 (m, 6 H), 8.82 (AB, J = 5.1 Hz, 2 H), 9.06 (AB, J = 15.8 Hz, 2 H), 9.22 (s, 2 H), 9.75 (d, J = 2.4 Hz, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -81.30 (s, 2 F), -98.44 (s, 2 F). UV-vis: λ_max (relative intensity, CH₂Cl₂) = 632 (1.0), 578 (4.2), 519 (8.3), 416 (225.6). MS (MALDI): m/z = 637 (MH⁺). HRMS (MALDI): m/z calcd for C₄₀H₂₄F₄N₄·H⁺: 637.2015; found: 637.2010.

Hydrolysis of 5,10,15-Triaryl-2,20-(hexafluoropropane-diyl)porphinato Zinc(II) Zn5 and 5,10,15- Triaryl-2,20-(tetrafluoroethanediyl)porphinato Zinc(II) (Zn7a) A sample of Zn5 or Zn7a (15 mg)was dissolved in CH₂Cl₂ (10 mL), then silica gel (300-400 mesh) was added. The solvent was evaporated to dryness. The powder was exposed to air for 1 h, then subjected immediately to chromatography (silica, CH₂Cl₂). The green band was collected to yield Zn8 or Zn9.
5,15-Diphenyl-10-(4-methylphenyl)-2,20-(20′-oxo)-(tetrafluoropropanediyl)porphinato Zinc (Zn8c)
IR (KBr): 1679 cm^-1 (C=O). ¹H NMR (300 MHz, CDCl₃): δ (ppm) = 7.77-7.83 (m, 6 H), 7.80 (AB, J = 70.5 Hz, 4 H), 8.13-8.21 (m, 4 H), 8.78-8.83 (m, 2 H), 8.90 (t, J = 4.2 Hz, 2 H), 9.02 (d, J = 3 Hz, 1 H), 9.46 (s, 1 H), 10.26 (d, J = 2.6 Hz, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -102.16 (t, J = 13.0 Hz, 2 F, β-CF₂), -121.35 (t, J = 14.1 Hz, 2 F, CF₂CO). UV-Vis: λ_max (relative intensity, CH₂Cl₂) = 628 (2.2), 578 (1.0), 441 (26.4). MS (MALDI): m/z = 740 (M⁺). HRMS (MALDI): m/z calcd for C₄₂H₂₄F₄N₄OZn⁺: 740.1178; found: 740.1172.
5,10,15-Triphenyl-2,20-(20′-oxo)-(difluoroethane-diyl)porphinato Zinc(II) (Zn9a)
IR (KBr): 1661 cm^-1 (C=O). ¹H NMR (300 MHz, CDCl₃): δ (ppm) = -1.88 (s, 2 H), 7.74-7.87 (m, 9 H), 8.15-8.22 (m, 6 H), 8.64 (AB, J = 10.8 Hz, 2 H), 8.87 (AB, J = 5.1 Hz, 2 H), 9.10 (d, J = 3 Hz, 1 H), 9.36 (s, 1 H), 10.40 (d, J = 2.4 Hz, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): δ (ppm) = -93.91 (s, 2 F). UV-Vis: λ _max (relative intensity, CH₂Cl₂) = 627 (1.1), 604 (1.0), 561 (1.0), 437 (33.0). MS (MALDI): m/z = 676 (M⁺). HRMS (MALDI): m/z calcd for C₄₀H₂₂F₂N₄OZn⁺: 676.1053; found: 676.1048.
Demetalation of 5,10,15-Triaryl-2,20-(20′-oxo)-(tetrafluoropropanediyl)porphinato Zinc(II) (Zn8) and 5,10,15-Triphenyl-2,20-(20′-oxo)-(difluoroethane-diyl)porphinato Zinc(II) (Zn9a) A sample of Zn8 or Zn9a (20 mg)was dissolved in CH₂Cl₂ (30 mL) and treated with concentrated sulfuric acid (several drops) for 5 min. The organic layer was washed with water several times and dried over anhydrous sodium sulfate. After evaporation of the solvent, 8 or 9a (90%) was isolated as a blue-purple solid.
5,15-Diphenyl-10-(4-methylphenyl)-2,20-(20′-oxo)-(tetrafluoropropanediyl)porphyrin ( 8c)
IR (KBr): 1683 cm^-1 (C=O). ¹H NMR (300 MHz, CDCl₃): d (ppm)= -1.80 (s, 2 H), 2.71 (s, 3 H), 7.82 (AB, J = 70.5 Hz, 4 H), 7.79-7.88 (m, 6 H), 8.15-8.23 (m, 4 H), 8.66 (AB, J = 16.8 Hz, 2 H), 8.89 (AB, J = 11.1 Hz, 2 H), 9.11 (d, J = 2.6 Hz, 1 H), 9.37 (t, J = 2.3 Hz, 1 H), 10.40 (d, J = 2.7 Hz, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): d (ppm) = -102.34 (t, J = 13.8 Hz, 2 F, β-CF₂), -121.21 (t, J = 13.8 Hz, 2 F,
-CF₂CO). UV-Vis: l_max (relative intensity, CH₂Cl₂) = 655 (1.3), 585 (1.7), 538 (1.0), 432 (31.1). MS (MALDI): m/z = 679 (MH⁺). HRMS (MALDI): m/z calcd for C₄₂H₂₆F₄N₄O·H⁺: 679.2121; found: 679.2116.
5,10,15-Triphenyl-2,20-(20′-oxo)-(difluoroethane-diyl)porphyrin ( 9a)
IR (KBr): 1710 cm^-1 (C=O). ¹H NMR (300 MHz, CDCl₃): d (ppm) = -2.57 (s, 1 H), -1.45 (s, 1 H), 7.68-7.79 (m, 9 H), 8.12-8.21 (m, 6 H), 8.69 (s, 2 H), 8.94 (AB, J = 9.6 Hz, 2 H), 9.15 (t, J = 1.5 Hz, 1 H), 9.24 (s, 1 H), 10.15 (d, J = 1.5 Hz, 1 H). ¹⁹F NMR (282 MHz, CDCl₃): d (ppm) = -93.81 (s, 2 F). UV-Vis λ_max (relative intensity, CH₂Cl₂) = 641 (1.0), 588 (2.3), 537 (1.7), 429 (54.6). MS (MALDI): m/z = 615 (MH⁺). HRMS (MALDI): m/z calcd for C₄₀H₂₄F₂N₄O·H⁺: 615.1996; found: 615.1991.

<A NAME="RU03605ST-16">16</A> Zhou QL. Huang YZ. J. Fluorine Chem. 1989, 43: 385

<A NAME="RU03605ST-17">17</A> Zhou QL. Huang YZ. J. Fluorine Chem. 1988, 39: 87