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Synlett 2005(6): 0963-0970  
DOI: 10.1055/s-2005-864833
LETTER
© Georg Thieme Verlag Stuttgart · New York

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

Liang Chena, Li-Mei Jinb, 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;
Further Information

Publication History

Received 31 January 2005
Publication Date:
23 March 2005 (online)

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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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10

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:
λmax (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: lmax (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: λmax (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: λmax (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.

13

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: λmax (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: λmax (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.

14

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: λmax (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: λmax (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.

15

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: λmax (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: lmax (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 λmax (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.