Borylated Thiaporphyrin Building Blocks for the Synthesis of Unsymmetrical Phenyl-Bridged Porphyrin Dyads

Abstract

meso-(4-Borylphenyl)thiaporphyrin building blocks with N₃S and N₂S₂ porphyrin cores have been synthesized using two different approaches and used for the synthesis of meso-meso- and β-meso-1,4-phenylene-bridged unsymmetrical porphyrin dyads containing two different porphyrin subunits.

Key words

thiaporphyrins - borylation - building blocks - porphyrin dyads - energy transfer

References and Notes

• 1 Hyslop AG. Kellet MA. Iovine PM. Therien MJ. J. Am. Chem. Soc.  1998,  120:  12676 
• 2a Aratani N. Osuka A. Org. Lett.  2001,  3:  4213 
• 2b Aratani N. Cho HS. Ahn TK. Cho S. Kim D. Sumi H. Osuka A. J. Am. Chem. Soc.  2003,  125:  9668 
• 2c Hata H. Shinokubo H. Osuka A. J. Am. Chem. Soc.  2005,  127:  8264 
• 2d Hata H. Yamaguchi S. Mori G. Nakazono S. Katoh T. Takatsu K. Hiroto S. Shinokubo H. Osuka A. Chem. Asian J.  2007,  2:  849 
• 3a Zhou X. Tse MK. Wan TSM. Chan KS. J. Org. Chem.  1996,  61:  3590 
• 3b Zhou X. Chan KS. J. Org. Chem.  1998,  63:  99 
• 3c Zhou X. Chan KS. J. Chem. Soc., Chem. Commun.  1994,  2493 
• 3d Zhang C. Suslick KS.
  J. Porphyrins Phthalocyanines  2005,  9:  659 
• 3e Deng Y. Chang CK. Nocera DG. Angew. Chem. Int. Ed.  2000,  39:  1066 
• 3f Bringmann G. Rüdenauer S. Götz DCG. Gulder TAM. Reichert M. Org. Lett.  2006,  8:  4743 
• 3g Bringmann G. Götz DCG. Gulder TAM. Gehrke TH. Bruhn T. Kupfer T. Radacki K. Braunschweig H. Heckmann A. Lambert C. J. Am. Chem. Soc.  2008,  130:  17812 
• 4a Punidha S. Sinha J. Kumar A. Ravikanth M. J. Org. Chem.  2008,  73:  323 
• 4b Rai S. Ravikanth M. J. Org. Chem.  2008,  73:  8364 
• 4c Punidha S. Ravikanth M. Tetrahedron  2008,  64:  8016 
• 5 Gupta I. Ravikanth M. Coord. Chem. Rev.  2006,  250:  468 ; and references cited therein
• 6 Gupta I. Ravikanth M. J. Org. Chem.  2004,  69:  6796 
• 7 Lindsey JS. Schreiman IC. Hsu HC. Kearney PC. Marguerettaz AM. J. Org. Chem.  1987,  52:  827 
• 8 Heo PY. Shin K. Lee CH. Bull. Korean Chem. Soc.  1996,  17:  515 
• 9 Punidha S. Agarwal N. Burai R. Ravikanth M. Eur. J. Org. Chem.  2004,  2223 
• 10 Callot HJ. Tetrahedron Lett.  1973,  14:  4987 

11

Experimental Procedure and Spectroscopic Data for Selected Compounds. Diol 3: Thiophene mono-alcohol 4 (0.96 g, 4.7 mmol), TMEDA (1.76 mL, 11.7 mmol) and n-BuLi (7.34 mL, ˜15% in hexane) were added successively to freshly distilled anhydrous Et₂O (30 mL) in a 250-mL three-necked, round-bottomed flask and stirred for 45 min under nitrogen atmosphere at 0 ˚C. An ice-cold solution of 4-formylboronic ester (1.25 g, 5.7 mmol) in THF (30 mL) was added and the mixture was stirred for an additional 45 min. The reaction was quenched with ice-cold NH₄Cl (50 mL, ˜1 M) and the organic layer was separated from the aqueous layer. The aqueous layer was extracted several times with Et₂O and the combined organic layers were washed thoroughly with water and brine and dried with anhydrous Na₂SO₄. The solvent was removed on a rotary evaporator under reduced pressure to afford the crude compound. TLC analysis showed three minor and one major spot corresponding to the unreacted 4-formylphenylboronic ester, unreacted mono-alcohol 4, unidentified compound and the desired diol 3. The crude compound was subjected to silica gel column chromatography (petroleum ether-EtOAc, 80:20). The aldehyde, the mono-alcohol 4 and the minor unidentified compound were removed and the desired diol 3 was collected (petroleum ether-EtOAc, 70:30) as yellow oily liquid (0.60 g, 30%). ^¹H NMR (400 MHz, CDCl₃): δ = 1.03 (s, 6 H, CH₃), 2.34 (s, 3 H, CH₃), 3.50 (br s, 2 H, OH), 3.76 (s, 4 H, CH₂), 5.92-5.96 (m, 2 H, CHOH), 6.67-6.69 (m, 2 H, thiophene), 7.28-7.30 (m, 2 H, ArH), 7.40 (d, J = 7.0 Hz, 2 H, ArH), 7.77-7.79 (m, 4 H, ArH). ^¹³C NMR (100 MHz, CDCl₃): δ = 22.5, 65.8, 71.5, 120.1, 124.3, 124.5, 125.5, 128.1, 129.3, 134.6, 136.1, 139.5, 140.2, 143.7, 145.6, 146.0, 149.7, 152.8, 155.6 ppm. ES-MS: m/z calcd for C₂₄H₂₇BO₄S: 422.1; found: 351.1 (100) [M - C₅H₁₁]⁺. Anal. Calcd for C₂₄H₂₇BO₄S: C, 68.25; H, 6.44. Found: C, 68.30; H, 6.37.
Porphyrin 6: A solution of diol 3 (0.5 g, 1.2 mmol), p-tolualdehyde (0.3 mL, 2.4 mmol) and pyrrole (0.25 mL, 3.6 mmol) in CH₂Cl₂ (300 mL) were condensed in the presence of BF₃˙OEt₂ (396 mL, 2.5 M) under an inert atmosphere. After 1 h, DDQ (0.272 g, 1.2 mmol) was added and the reaction was stirred in open air for an additional 1 h. TLC analysis indicated the formation of a mixture of four porphyrins: tetra(p-tolyl)porphyrin (H₂TTP), the desired mono-functionalized 21-thiaporphyrin boronic acid 6 and a cis and trans mixture of 21,23-dithiaporphyrin boronic acid. The crude mixture of porphyrins was subjected to silica gel column chromatography and the fast moving H₂TTP was removed with petroleum ether-CH₂Cl₂ (80:20). The desired 6 was collected as a second band using petroleum ether-CH₂Cl₂ (40:60) and the cis and trans mixture of porphyrins was collected in CH₂Cl₂. The solvent was removed on a rotary evaporator to afford H₂TTP (3%), the desired compound 6 (8%) and the cis and trans mixture (<1%). ^¹H NMR (400 MHz, CDCl₃): δ = -2.69 (s, 1 H, NH), 2.69 (s, 9 H, CH₃), 7.23 (d, J = 8.2 Hz, 2 H, ArH), 7.54 (d, J = 7.6 Hz, 4 H, ArH), 7.61 (d, J = 7.6 Hz, 2 H, ArH), 8.06-8.14 (m, 8 H, ArH), 8.67 (d, J = 4.6 Hz, 2 H, β-pyrrole), 8.68 (d, J = 4.6 Hz, 2 H, β-pyrrole), 8.93 (s, 2 H, β-pyrrole), 9.75 (s, 2 H, β-thiophene). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.8, 31.2, 103.2, 120.9, 121.3, 123.6, 128.4, 128.5, 129.2, 130.4, 133.2, 134.3, 134.7, 135.2, 135.9, 136.9, 138.1, 138.4, 145.8, 148.3, 154.1, 156.8, 157.1, 157.6. ES-MS: m/z calcd for C₄₇H₃₆BN₃O₂S: 717.3; found: 718.3 (100%) [M + 1]⁺. UV/Vis (CH₂Cl₂): λ_max (log ε) = 431 (5.89), 515 (4.59), 551 (4.16), 619 (3.66), 680 nm (3.95).
Porphyrin 7: Samples of diol 3 (0.4 g, 0.95 mmol) and tripyrrane 5 (0.398 g, 0.95 mmol) in CH₂Cl₂ (250 mL) were condensed in the presence of BF₃˙OEt₂ (200 mL, 2.5 M) under inert atmosphere for 1 h. DDQ (0.216 g, 0.95 mmol) was added and stirring was continued for additional 1 h in open air. TLC analysis showed the formation of the desired product 7 as the sole product. Chromatography on silica (petroleum ether-CH₂Cl₂, 50:50) gave porphyrin 7 as a purple solid (0.08 g, 11%). ^¹H NMR (400 MHz, CDCl₃): δ = 2.70 (s, 9 H, CH₃), 7.21 (d, J = 7.6 Hz, 2 H, ArH), 7.61 (d, J = 7.6 Hz, 6 H, ArH), 8.08 (d, J = 7.6 Hz, 6 H, ArH), 8.23 (s, 2 H, ArH), 8.67 (s, 4 H, β-pyrrole), 9.95 (s, 4 H, β-thiophene). ^¹³C NMR (100 MHz, CDCl₃): δ = 22.6, 22.8, 31.1, 31.5, 128.0, 129.5, 133.6, 134.7, 134.9, 135.1, 135.7, 136.1, 138.0, 146.8, 147.6, 148.5, 148.7, 149.8, 150.9, 155.1, 157.1. ES-MS: m/z calcd for C₄₇H₃₅BN₂O₂S₂: 734.2; found: 735.6 (100%) [M + 1]⁺. UV/Vis (CH₂Cl₂): λ_max (log ε) = 437 (5.83), 515 (4.67), 550 (4.27), 634 (3.55), 698 nm (4.01).
Porphyrin 1: Method 1: Compound 6 (0.04 g, 0.055 mmol) was treated with 2,2-dimethylpropane-1,3-diol (0.009 g, 0.083 mmol) in THF (15 mL) at r.t. for 2 h. Flash column chromatography (CH₂Cl₂) afforded porphyrin boronic ester 1 in 97% yield.
Borylated thiaporphyrin building blocks for the synthesis of unsymmetrical phenyl bridged porphyrin dyads: Method 2: The meso-brominated thiaporphyrin 10 (0.03 g, 0.044 mmol) was treated with phenyl diboronic ester 12 (0.04 g, 0.13 mmol) in toluene-triethylamine (5:1) in the presence of catalytic amounts of Pd(PPh₃)₄ (0.005 g, 0.004 mmol) and Cs₂CO₃ (0.016 g, 0.066 mmol) at 80 ˚C for 2 h. After standard work-up, the crude compound was purified by silica gel column chromatography (petroleum ether-CH₂Cl₂, 60:40) to afford the porphyrin boronic ester 1 in 51% yield. ^¹H NMR (400 MHz, CDCl₃): δ = -2.69 (s, 1 H, NH), 1.16 (s, 6 H, CH₃), 2.69 (s, 9 H, CH₃), 3.93 (s, 4 H, CH₂), 7.23 (d, J = 8.2 Hz, 2 H, ArH), 7.54 (d, J = 7.6 Hz, 4 H, ArH), 7.61 (d, J = 7.6 Hz, 2 H, ArH), 8.06-8.14 (m, 8 H, ArH), 8.67 (d, J = 4.6 Hz, 2 H, β-pyrrole), 8.68 (d, J = 4.6 Hz, 2 H, β-pyrrole), 8.93 (s, 2 H, β-pyrrole), 9.75 (s, 2 H, β-thiophene). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.8, 31.2, 103.2, 120.9, 121.3, 123.6, 128.4, 128.5, 129.2, 130.4, 133.2, 134.3, 134.7, 135.2, 135.9, 136.9, 138.1, 138.4, 145.8, 148.3, 154.1, 156.8, 157.1, 157.6. ES-MS: m/z calcd for C₅₂H₄₄BN₃O₂S: 785.3; found: 786.4 (100%) [M + 1]⁺. Anal. Calcd for C₅₂H₄₄BN₃O₂S: C, 79.48; H, 5.64; N, 5.35. Found: C, 79.53; H, 5.68; N, 5.30.
Porphyrin 2: Porphyrin 2 was synthesized in 58% yield following same experimental conditions used for the synthesis of porphyrin 1. ^¹H NMR (400 MHz, CDCl₃): δ = 1.16 (s, 6 H, CH₃), 2.70 (s, 9 H, CH₃), 3.96 (s, 4 H, CH₂), 7.21 (d, J = 7.6 Hz, 2 H, ArH), 7.61 (d, J = 7.6 Hz, 6 H, ArH), 8.08 (d, J = 7.6 Hz, 6 H, ArH), 8.23 (s, 2 H, ArH), 8.67 (s, 4 H, β-pyrrole), 9.95 (s, 4 H, β-thiophene). ^¹³C NMR (100 MHz, CDCl₃): δ = 22.6, 22.8, 31.1, 31.5, 128.0, 129.5, 133.6, 134.7, 134.9, 135.1, 135.7, 136.1, 138.0, 146.8, 147.6, 148.5, 148.7, 149.8, 150.9, 155.1, 157.1. MALDI-TOF: m/z calcd for C₅₂H₄₃BN₂O₂S₂: 802.3; found: 802.1 (100%) [M]⁺. Anal. Calcd for C₅₂H₄₃BN₂O₂S₂: C, 77.79; H, 5.40; N, 3.49. Found: C, 77.85; H, 5.38; N, 3.52.
General procedure for dyads 13 and 14: Samples of meso-bromo N₃S porphyrin 10/β-bromo ZnN₄ porphyrin 15 and N₂S₂ porphyrin boronic ester 2 or N₂S₂ porphyrin boronic acid 7 were dissolved in anhydrous toluene-triethylamine (6 mL, 5:1) in a 25-mL two-necked, round-bottomed flask under a nitrogen atmosphere. Cs₂CO₃ (1.5 equiv) followed by Pd(PPh₃)₄ (0.1 equiv) were added and the resulting mixture was heated at 80 ˚C for 4 h. After work-up, the crude compound was subjected to silica gel chromatography to afford dyads 13 and 14 as purple solids in reasonable yields.
Spectral data for compounds 13 and 14:
Compound 13: Yield: 78%. ^¹H NMR (400 MHz, CDCl₃):
δ = -2.55 (s, 1 H, NH), 2.64 (t, J = 7.9 Hz, 18 H, CH₃), 7.47 (d, J = 7.6 Hz, 2 H, ArH), 7.50-7.54 (m, 10 H, ArH), 7.58 (d, J = 7.6 Hz, 2 H, ArH), 7.99 (d, J = 7.9 Hz, 2 H, ArH), 8.03-8.12 (m, 12 H, ArH), 8.52 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.59 (s, 2 H, β-pyrrole), 8.61-8.62 (m, 2 H, β-pyrrole), 8.64 (d, J = 4.6 Hz, 1 H, β-pyrrole), 8.70 (d, J = 4.3 Hz, 1 H,
β-pyrrole), 8.87 (dd, J = 10.7, 2.1 Hz, 2 H, β-pyrrole), 9.19 (d, J = 4.6 Hz, 1 H, β-pyrrole), 9.59 (s, 2 H, β-thiophene), 9.63 (d, J = 4.9 Hz, 1 H, β-thiophene), 9.69 (d, J = 5.2 Hz, 1 H, β-thiophene), 9.79 (d, J = 5.2 Hz, 1 H, β-thiophene), 10.22 (d, J = 5.2 Hz, 1 H, β-thiophene). ^¹³C NMR (100 MHz, CDCl₃): δ = 21.7, 22.9, 34.0, 53.6, 114.3, 115.1, 121.3, 127.5, 128.6, 129.3, 131.9, 132.0, 134.4, 134.8, 135.8, 137.2, 140.1, 146.5, 148.9, 150.5, 150.9, 154.9. MALDI-TOF: m/z calcd for C₈₈H₆₃N₅S₃: 1285.4; found: 1285.6 (100%) [M]⁺. Anal. Calcd for C₈₈H₆₃N₅S₃: C, 82.15; H, 4.94; N, 5.44. Found: C, 82.21; H, 4.85; N, 5.41.
Compound 14: Yield: 58%. ^¹H NMR (400 MHz, CDCl₃):
δ = 2.63 (s, 21 H, CH₃), 7.35-7.39 (m, 4 H, ArH), 7.52-7.54 (m, 8 H, ArH), 7.62 (d, J = 7.7 Hz, 6 H, ArH), 7.69-7.71 (m, 6 H, ArH), 7.93 (d, J = 7.0 Hz, 2 H, ArH), 8.05 (d, J = 7.0 Hz, 2 H, ArH), 8.13 (d, J = 7.4 Hz, 4 H, ArH), 8.32 (d, J = 4.0 Hz, 2 H, β-pyrrole), 8.69-8.71 (m, 4 H, β-pyrrole), 8.74-8.76 (m, 2 H, β-pyrrole), 8.84 (s, 1 H, β-pyrrole), 9.42 (s, 1 H, β-pyrrole), 9.54 (s, 1 H, β-pyrrole), 9.70 (s, 2 H, β-thiophene), 9.73 (d, J = 5.2 Hz, 2 H, β-thiophene). ^¹³C NMR (100 MHz, CDCl₃): δ = 23.7, 110.8, 114.8, 118.2, 126.3, 128.5, 128.3, 129.0, 129.4, 130.6, 131.0, 132.0, 132.7, 133.6, 134.4, 135.2, 135.7, 136.3, 137.0, 137.6, 141.3, 143.1, 146.3, 155.5. MALDI-TOF: m/z calcd for C₉₆H₇₀N₆S₂Zn: 1434.4; found: 1434.5 (100%) [M]⁺. Anal. Calcd for C₉₆H₇₀N₆S₂Zn: C, 80.23; H, 4.91; N, 5.85. Found: C, 80.15; H, 5.01; N, 5.78.