- Email: [email protected]
Synthesis of π-extended platinum porphyrins
Tetrahedron Letters 56 (2015) 7043–7045
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Synthesis of p-extended platinum porphyrins Satoshi Ito ⇑, Daishi Makihata, Yutaro Ishii, Yuki Saito, Toru Oba Department of Applied Chemistry, Faculty of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya, Tochigi 321-8585, Japan
a r t i c l e
i n f o
Article history: Received 1 October 2015 Revised 2 November 2015 Accepted 6 November 2015 Available online 7 November 2015
a b s t r a c t We report the efficient synthesis of tetrabicycloporphyrin platinum under mild conditions (60 °C). The platinum complexes were heated under vacuum to give p-extended platinum porphyrins in 100% yield. The porphyrins are expected to have interesting properties such as high-quantum-efficiency near-IR phosphorescence and large absorptivity in the near-IR region. Ó 2015 Elsevier Ltd. All rights reserved.
Keywords: Porphyrin Retro Diels–Alder reaction Phosphorescence Organic semiconductor Platinum complex
Introduction
Results and discussion
Platinum porphyrins have been widely used as phosphorescent labels,1 oxygen sensors,2 organic thin-film transistors,3 and organic electroluminescent materials.4 Various types of platinum porphyrins have been synthesized.5 Synthesis of p-extended platinum porphyrins has also produced meso-substituted derivatives with good solubility.6 These porphyrins are expected to have interesting properties such as high-quantum-efficiency near-IR phosphorescence and large absorptivity in the near-IR region. However, platinum complexes of meso-unsubstituted p-extended porphyrins, such as tetrabenzoporphyrin (BP, 1), [2,3]tetranaphthoporphyrin (NP, 2), and [2,3]tetraanthraporphyrin (AP, 3), have not been synthesized (Fig. 1). We previously reported that when tetrabicycloporphyrins (CP: 4, BCP: 5, NCP: 6) and their metal complexes are heated, they can be converted to p-extended porphyrins 1–3 in 100% yield.7 Tetrabicycloporphyrins 4–6 are soluble in organic solvents such as chloroform, ethyl acetate, and ethanol. If platinum bicycloporphyrins (4-Pt, 5-Pt, 6-Pt) are synthesized, p-extended platinum porphyrins (1-Pt, 2-Pt, 3-Pt) can be also prepared. However, introducing platinum into the porphyrin core usually requires high temperatures, which results in pyrolysis of the bicyclo[2.2.2] octadiene (BCOD) ring. Moreover, platinum acts as an oxidizing agent owing to its low ionization tendency, and the thermal decomposition of the BCOD ring proceeds even at low temperatures.8 We report the synthesis of p-extended platinum porphyrins under mild conditions via soluble precursors.
In general, platinum porphyrins are prepared by treating freebase porphyrin with PtCl2 in high-boiling solvents, such as PhCN or DMF, at temperatures of 180 °C or above.9 Bicycloporphyrins 4–6 underwent the pyrolysis of the BCOD ring and ring-opening of the porphyrin core under these reaction conditions. Next, we tried a milder complexation method. Bicycloporphyrin 5 with a relatively high thermal stability was successfully converted into platinum complex 5-Pt by refluxing PtCl2 in glacial acetic acid (bp = 118 °C) in a yield of 39% (Scheme 1: Method A). However, no 4-Pt was produced by this method, and only a mixture containing BP (1) was obtained.10 Under acidic or oxidative conditions, the thermal decomposition of BCOD rings can occur at a much lower temperature than under neutral or basic conditions. Complexation of CP (4) did not proceed at low temperatures (room temperature to 70 °C) in this reaction, and the starting material was recovered. From the above results, we concluded that the following three factors are important: (i) a low reaction temperature during the complexation; (ii) using a platinum salt that is soluble in the solvent; and (iii) keeping the reaction solution basic. We investigated a reaction similar to the titanylation and vanadylation with a metal chloride and strong base.11 When PtCl2 and CP (4) reacted with LiHMDS as the base in toluene at 45 °C, a trace amount of 4-Pt was observed. Next, we focused on the synthesis of [Pt4(OAc)82HOAc] from PtCl2 and Ag(OAc).12 [Pt4(OAc)82HOAc] is suitable for complexation of porphyrins that are soluble in chloroform, and replacement of the ligand or counteranion occurs at relatively low temperatures. When CP (4) reacted with 1.0 equiv of [Pt4(OAc)82HOAc] in chloroform at 60 °C for
⇑ Corresponding author. Tel.: +81 28 689 7013; fax: +81 28 689 6009. E-mail address: [email protected] (S. Ito). http://dx.doi.org/10.1016/j.tetlet.2015.11.018 0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
7044
S. Ito et al. / Tetrahedron Letters 56 (2015) 7043–7045
NH N
N
NH N
HN
tetrabenzoporphyrin (BP:1)
NH N
N
NH N
HN
N HN
[2,3]tetraanthraporphyrin (AP: 3)
[2,3]tetranaphthoporphyrin (NP: 2)
N
NH N
HN
CP (4)
N
NH N
HN
N HN
BCP (5)
NCP (6)
Figure 1. p-Extended porphyrins and bicycloporphyrins.
n
NH
N
N
HN
PtCl2, AcONa
N
AcOH, reflux, 48 h 39%
N
N
N
Pt
Pt
N
n
n
N
N
Scheme 1. Method A.
N
N N
n
4-Pt (n = 0) 5-Pt (n = 1) 6-Pt (n = 2)
5-Pt
Pt
100%
n
5
N
220-300 ഒ , 1 h
N
n
n
1-Pt (n = 0) 2-Pt (n = 1) 3-Pt (n = 2)
n
Scheme 3.
48 h under Ar, target 4-Pt was obtained in 3% yield. Under similar reaction conditions, the yield of 4-Pt was increased to 25% by the addition of 10 equiv of CH3CO2Na as buffer (Scheme 2: Method B).13 5-Pt and 6-Pt were also obtained by using this method in 20% and 15% yields, respectively. Platinum bicycloporphyrins (1-Pt, 2-Pt, 3-Pt) were obtained in 100% yield by heating the corresponding p-extended platinum porphyrins at 220–300 °C for 1 h under inert gas (Scheme 3). UV–vis spectra of the platinum bicycloporphyrins (4-Pt, 5-Pt, and 6-Pt) and tetrabenzoporphyrin platinum (1-Pt) were recorded. The absorption maxima of the platinum porphyrins were blueshifted compared with freebase CP (4) because of the back donation effects of Pt, and there was no increase in the extinction coefficient. The absorption characteristics were similar to typical metal complexes. In contrast, the extinction coefficient of 1-Pt increased
n
n
n
NH N
N HN
n
[Pt4(OAc)8. 2HOAc]
N
AcONa CHCl3, 60 ഒ , 48 h
N
N Pt N
n
n
4 (n = 0) 5 (n = 1) 6 (n = 2)
n
4-Pt (n = 0): 25% 5-Pt (n = 1): 20% 6-Pt (n = 2): 15% Scheme 2. Method B.
n
significantly compared with typical BP metal complexes. In particular, there was a large increase in the extinction coefficient of the Q band in 1-Pt (kmax = 596 nm, log e = 5.03; in pyridine) (Fig. 2).14 UV–vis spectra of p-extended platinum porphyrins (2-Pt, 3-Pt) were not obtained because they did not readily dissolve in any solvents. The oxidation potentials of platinum bicycloporphyrins (4-Pt, 5-Pt, 6-Pt) were determined by cyclic voltammetry. The first oxidation potentials increased substantially (4-Pt: Eox1/2(1) = 0.515 V; 5-Pt: Eox1/2(1) = 0.609 V; 6-Pt: Eox1/2(1) = 0.658 V vs Ag/AgNO3, 0.1 M TBAP in PhCN, Fc = +0.076 V) compared with freebase CP (1) (Eox1/2(1) = +0.287 V, Eox1/2(2) = +0.699 V). The increase of the first oxidation potentials is not only the effect of the r–p conjugation, but also that of platinum coordination since 4-Pt also exhibited the increase of the oxidation potential compared to the freebase form.15 The oxidation potentials of the p-extended platinum porphyrins (1-Pt, 2-Pt, 3-Pt) were not obtained because they did not readily dissolve in any solvents. We used solution-based fabrication to make an FET device with 4-Pt, which was then converted to 1-Pt. The FET device containing 1-Pt was fabricated as follows.16 The source and drain electrodes were formed on a 300-nm-thick layer of thermally grown SiO2 on a Sb-doped n-type Si substrate (capacitance = 11.5 nF cm 2) by photolithography of Au (90 nm)/Cr (10 nm) layers. The standard channel length and width were 10 and 100 lm, respectively. The channels were spin coated with a 0.7 wt % CHCl3 solution of 4-Pt. The film was converted into 1-Pt by heating at 210 °C for 20 min. The devices were fabricated under a dry N2 atmosphere. The
S. Ito et al. / Tetrahedron Letters 56 (2015) 7043–7045
7045
Figure 2. UV–vis spectra of (a) 4-Pt (red) in CHCl3; (b) 1-Pt (green) in pyridine.
devices based on 1-Pt showed FET characteristics (10 lm: l = 2.3 10 3 cm2/V s, 100 lm: l = 4.9 10 4 cm2/V s). Conclusions We have prepared p-extended platinum porphyrins via bicycloporphyrins with [Pt4(OAc)82HOAc] or followed by the retro Diels– Alder reaction. Our method requires milder conditions than established methods and should assist in developing new functional organic materials that contain porphyrin units.
9. 10.
11.
Acknowledgments
12.
This work was partially supported by Cooperative Research Program of ‘Network Joint Research Center for Materials and Devices’ (No. 2013A15: to S.I.) and the Takahashi Industrial and Economic Research Foundation (No. 150: to S.I.). We would also like to thank Dr. Saika Otsubo (Mitsubishi Chemical Group, Science and Technology Research Center, Inc.) for fabricating and testing the FET devices and Mr. Makoto Roppongi (the Collaboration Center for Research and Development of Utsunomiya University) and Mr. Tomokichi Onoda (Shimamura Tech. Co.: Preparative HPLC Systems) for helping in experiments.
13.
References and notes 1. Borek, G.; Hanson, K.; Djurovich, P. I.; Thompson, M. E.; Aznavour, K.; Bau, R.; Sun, Y.; Forrest, S. R.; Brooks, J.; Michalski, L.; Brown, J. Angew. Chem., Int. Ed. 2007, 46, 1109–1112. 2. Papkovskii, D. B.; Savitskii, A. P.; Yaropolov, A. I.; Ponomarev, G. V.; Rumyantseva, V. D.; Mironov, A. F. Biomed. Sci. 1991, 2, 63–67. 3. Minari, T.; Seto, M.; Nemoto, T.; Isoda, S.; Tsukagoshi, K.; Aoyagi, Y. Appl. Phys. Lett. 2007, 91, 123501; Perez, M. D.; Borek, C.; Forrest, S. R.; Thompson, M. E. J. Am. Chem. Soc. 2009, 131, 9281–9286. 4. Noh, Y.; Lee, C.; Kim, J. J. Chem. Phys. 2003, 118, 2853–2864. 5. The Porphyrin HandbookInorganic, Organometallic and Coordination Chemistry; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 3, p 26. Chapter 15. 6. Sommer, J. R.; Shelton, A. H.; Parthasarathy, A.; Ghiviriga, I.; Reynolds, J. R.; Schanze, K. S. Chem. Mater. 2011, 23, 5296–5304. 7. Ito, S.; Murashima, T.; Uno, H.; Ono, N. Chem. Commun. 1998, 1661–1662; Ito, S.; Ochi, N.; Murashima, T.; Uno, H.; Ono, N. Chem. Commun. 2000, 893–894; Yamada, H.; Kuzuhara, D.; Takahashi, T.; Shimizu, Y.; Uota, K.; Okujima, T.; Uno, H.; Ono, N. Org. Lett. 2008, 10, 2947–2950. 8. Ito, S.; Phong, L.-T.; Komatsu, T.; Igarashi, N.; Otsubo, S.; Sakai, Y.; Ohno, A.; Aramaki, S.; Tanaka, Y.; Uno, H.; Oba, T.; Hiratani, K. Eur. J. Org. Chem. 2009, 31,
14.
15. 16.
5373–5382; Ito, S.; Terada, N.; Seino, K.; Makihata, D.; Sasaki, A.; Oba, T. Tetrahedron Lett. 2013, 54, 5916–5919. Buchler, J. W. In Porphyrins and Metalloporphyrins; Smith, K. M., Ed.; Elsevier: Amsterdam, 1975; p 157. Procedure for 5-Pt [Method A]: AcONa (50.0 mg, 608 lmol) was added to a suspension of bicycloporphyrin (5) (NCP: 5.00 mg, 6.08 lmol) and PtCl2 in AcOH (20 ml) and the mixture was refluxed for 24 h under Ar. The reaction was quenched with water and diluted with CHCl3. The organic layer was washed with saturated NaHCO3 aq (4), water (2) and brine (1), and dried over anhydrous Na2SO4. The solvent was removed and the reaction mixture was purified by column chromatography on silica gel 60 N (eluent CHCl3) followed by precipitation from methanol to give 2.40 mg (39%) of bicycloporphyrin platinum (5-Pt) as a red powder. Ito, S.; Ito, T.; Makihata, D.; Ishii, Y.; Saito, Y.; Oba, T. Tetrahedron Lett. 2014, 55, 4390–4394. Basato, M.; Biffis, A.; Martinati, G.; Tubaro, C.; Venzo, A.; Ganis, P.; Benetollo, F. Inorg. Chim. Acta 2003, 355, 299–403. General procedure for 4-Pt [Method B]: AcONa (0.140 g, 0.16 mol)/MeOH (10 ml) solution was added to a solution of bicycloporphyrin (1) (CP: 0.10 g, 0.16 mmol) and [Pt4(OAc)82AcOH] (250 mg, 0.18 mmol) in CHCl3 (130 ml) and the mixture was stirred at 60 °C for 48 h under Ar. The reaction was quenched with water and diluted with CHCl3. The organic layer was washed with water (2) and brine (1), and dried over anhydrous Na2SO4. The solvent was removed and the reaction mixture was purified by column chromatography on silica gel 60 N (eluent CHCl3) followed by precipitation from methanol to give 32.3 mg (25%) of bicycloporphyrin platinum (4-Pt) as a red powder. Selected experimental data for 4-Pt: Red powder, mp >200 °C (dec); 1H NMR (CDCl3, 500 MHz): d = 10.27 (s, 4H), 7.11 (s, 8H), 5.66 (s, 8H), 2.18 (m, 8H) ppm; UV–vis (CHCl3), kmax (log e): 382 (5.46), 498 (4.08), 532 (4.52) nm; MALDI-TOF (m/z) 817.61 (M+); calcd for C44H36N4Pt7/4CHCl39/4H2O. C, 53.37; H, 5.30; N, 4.55. Found: C, 53.91; H, 5.45; N, 4.22. For 5-Pt: Red powder, mp >280 °C (dec); 1H NMR (CDCl3, 500 MHz): d = 10.41 (s, 4H), 7.76 (s, 8H), 7.22 (s, 8H), 6.07 (m, 8H), 2.38–2.29 (m, 8H) ppm; UV–vis (CHCl3), kmax (log e): 384 (5.50), 499 (4.10), 532 (4.55) nm; MALDI-TOF (m/z) 1061.43 (M+); calcd for C60H44N4Pt1/ 2CHCl32H2O. C, 65.36; H, 4.40; N, 5.04. Found: C, 65.04; H, 4.42; N, 4.57. For 6-Pt: Red powder, mp >280 °C (dec); 1H NMR (CDCl3, 500 MHz): d = 10.48 (s, 4H), 8.21 (m, 8H), 7.88 (m, 8H), 7.44 (m, 8H), 6.21 (s, 8H), 2.51 (m, 8H), 2.39 (m, 8H) ppm; UV–vis (CHCl3), kmax (log e): 386 (5.36), 499 (4.01), 532 (4.43) nm; MALDI-TOF (m/z) 1215.73 (M+); calcd for C76H52N4Pt5/4CHCl39C2H5OH. C, 64.26; H, 6.07; N, 3.15. Found: C, 64.59; H, 6.40; N, 6.05. General procedure for 1-Pt: Bicycloporphyrin platinum (4-Pt) was heated in a glass tube oven under vacuum at 220 °C for 1 h to give corresponding tetrabenzoporphyrin platinum (1-Pt) in 100% yield. Selected experimental data for 1-Pt: Green powder, mp >200 °C; UV–vis (CHCl3), kmax (log e): 396 (4.99), 542 (4.03), 596 (5.03) nm; MALDI-TOF (m/z) 704.13 (M+); calcd for C36H20N4PtH2O. C, 59.92; H, 3.07; N, 7.76. Found: C, 60.22; H, 2.99; N, 8.01. For 2-Pt: Green powder, mp >200 °C; MALDI-TOF (m/z) 903.18 (M+); calcd for C52H28N4Pt3/2H2O. C, 67.09; H, 3.36; N, 6.02. Found: C, 67.32; H, 3.76; N, 5.89. For 3-Pt: Green powder, mp >200 °C; MALDI-TOF (m/z) 1103.20 (M+); calcd for C68H36N4Pt27/2H2O. C, 60.62; H, 4.71; N, 4.16. Found: C, 60.64; H, 5.07; N, 4.21. Ito, S.; Watanabe, H.; Uno, H.; Murashima, T.; Ono, N.; Tsai, Y.-C.; Compton, R. G. Tetrahedron Lett. 2001, 42, 707–710. Aramaki, S.; Sakai, Y.; Ono, N. Appl. Phys. Lett. 2004, 84, 2085.
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Synthesis of p-extended platinum porphyrins Satoshi Ito ⇑, Daishi Makihata, Yutaro Ishii, Yuki Saito, Toru Oba Department of Applied Chemistry, Faculty of Engineering, Utsunomiya University, 7-1-2 Yoto, Utsunomiya, Tochigi 321-8585, Japan
a r t i c l e
i n f o
Article history: Received 1 October 2015 Revised 2 November 2015 Accepted 6 November 2015 Available online 7 November 2015
a b s t r a c t We report the efficient synthesis of tetrabicycloporphyrin platinum under mild conditions (60 °C). The platinum complexes were heated under vacuum to give p-extended platinum porphyrins in 100% yield. The porphyrins are expected to have interesting properties such as high-quantum-efficiency near-IR phosphorescence and large absorptivity in the near-IR region. Ó 2015 Elsevier Ltd. All rights reserved.
Keywords: Porphyrin Retro Diels–Alder reaction Phosphorescence Organic semiconductor Platinum complex
Introduction
Results and discussion
Platinum porphyrins have been widely used as phosphorescent labels,1 oxygen sensors,2 organic thin-film transistors,3 and organic electroluminescent materials.4 Various types of platinum porphyrins have been synthesized.5 Synthesis of p-extended platinum porphyrins has also produced meso-substituted derivatives with good solubility.6 These porphyrins are expected to have interesting properties such as high-quantum-efficiency near-IR phosphorescence and large absorptivity in the near-IR region. However, platinum complexes of meso-unsubstituted p-extended porphyrins, such as tetrabenzoporphyrin (BP, 1), [2,3]tetranaphthoporphyrin (NP, 2), and [2,3]tetraanthraporphyrin (AP, 3), have not been synthesized (Fig. 1). We previously reported that when tetrabicycloporphyrins (CP: 4, BCP: 5, NCP: 6) and their metal complexes are heated, they can be converted to p-extended porphyrins 1–3 in 100% yield.7 Tetrabicycloporphyrins 4–6 are soluble in organic solvents such as chloroform, ethyl acetate, and ethanol. If platinum bicycloporphyrins (4-Pt, 5-Pt, 6-Pt) are synthesized, p-extended platinum porphyrins (1-Pt, 2-Pt, 3-Pt) can be also prepared. However, introducing platinum into the porphyrin core usually requires high temperatures, which results in pyrolysis of the bicyclo[2.2.2] octadiene (BCOD) ring. Moreover, platinum acts as an oxidizing agent owing to its low ionization tendency, and the thermal decomposition of the BCOD ring proceeds even at low temperatures.8 We report the synthesis of p-extended platinum porphyrins under mild conditions via soluble precursors.
In general, platinum porphyrins are prepared by treating freebase porphyrin with PtCl2 in high-boiling solvents, such as PhCN or DMF, at temperatures of 180 °C or above.9 Bicycloporphyrins 4–6 underwent the pyrolysis of the BCOD ring and ring-opening of the porphyrin core under these reaction conditions. Next, we tried a milder complexation method. Bicycloporphyrin 5 with a relatively high thermal stability was successfully converted into platinum complex 5-Pt by refluxing PtCl2 in glacial acetic acid (bp = 118 °C) in a yield of 39% (Scheme 1: Method A). However, no 4-Pt was produced by this method, and only a mixture containing BP (1) was obtained.10 Under acidic or oxidative conditions, the thermal decomposition of BCOD rings can occur at a much lower temperature than under neutral or basic conditions. Complexation of CP (4) did not proceed at low temperatures (room temperature to 70 °C) in this reaction, and the starting material was recovered. From the above results, we concluded that the following three factors are important: (i) a low reaction temperature during the complexation; (ii) using a platinum salt that is soluble in the solvent; and (iii) keeping the reaction solution basic. We investigated a reaction similar to the titanylation and vanadylation with a metal chloride and strong base.11 When PtCl2 and CP (4) reacted with LiHMDS as the base in toluene at 45 °C, a trace amount of 4-Pt was observed. Next, we focused on the synthesis of [Pt4(OAc)82HOAc] from PtCl2 and Ag(OAc).12 [Pt4(OAc)82HOAc] is suitable for complexation of porphyrins that are soluble in chloroform, and replacement of the ligand or counteranion occurs at relatively low temperatures. When CP (4) reacted with 1.0 equiv of [Pt4(OAc)82HOAc] in chloroform at 60 °C for
⇑ Corresponding author. Tel.: +81 28 689 7013; fax: +81 28 689 6009. E-mail address: [email protected] (S. Ito). http://dx.doi.org/10.1016/j.tetlet.2015.11.018 0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
7044
S. Ito et al. / Tetrahedron Letters 56 (2015) 7043–7045
NH N
N
NH N
HN
tetrabenzoporphyrin (BP:1)
NH N
N
NH N
HN
N HN
[2,3]tetraanthraporphyrin (AP: 3)
[2,3]tetranaphthoporphyrin (NP: 2)
N
NH N
HN
CP (4)
N
NH N
HN
N HN
BCP (5)
NCP (6)
Figure 1. p-Extended porphyrins and bicycloporphyrins.
n
NH
N
N
HN
PtCl2, AcONa
N
AcOH, reflux, 48 h 39%
N
N
N
Pt
Pt
N
n
n
N
N
Scheme 1. Method A.
N
N N
n
4-Pt (n = 0) 5-Pt (n = 1) 6-Pt (n = 2)
5-Pt
Pt
100%
n
5
N
220-300 ഒ , 1 h
N
n
n
1-Pt (n = 0) 2-Pt (n = 1) 3-Pt (n = 2)
n
Scheme 3.
48 h under Ar, target 4-Pt was obtained in 3% yield. Under similar reaction conditions, the yield of 4-Pt was increased to 25% by the addition of 10 equiv of CH3CO2Na as buffer (Scheme 2: Method B).13 5-Pt and 6-Pt were also obtained by using this method in 20% and 15% yields, respectively. Platinum bicycloporphyrins (1-Pt, 2-Pt, 3-Pt) were obtained in 100% yield by heating the corresponding p-extended platinum porphyrins at 220–300 °C for 1 h under inert gas (Scheme 3). UV–vis spectra of the platinum bicycloporphyrins (4-Pt, 5-Pt, and 6-Pt) and tetrabenzoporphyrin platinum (1-Pt) were recorded. The absorption maxima of the platinum porphyrins were blueshifted compared with freebase CP (4) because of the back donation effects of Pt, and there was no increase in the extinction coefficient. The absorption characteristics were similar to typical metal complexes. In contrast, the extinction coefficient of 1-Pt increased
n
n
n
NH N
N HN
n
[Pt4(OAc)8. 2HOAc]
N
AcONa CHCl3, 60 ഒ , 48 h
N
N Pt N
n
n
4 (n = 0) 5 (n = 1) 6 (n = 2)
n
4-Pt (n = 0): 25% 5-Pt (n = 1): 20% 6-Pt (n = 2): 15% Scheme 2. Method B.
n
significantly compared with typical BP metal complexes. In particular, there was a large increase in the extinction coefficient of the Q band in 1-Pt (kmax = 596 nm, log e = 5.03; in pyridine) (Fig. 2).14 UV–vis spectra of p-extended platinum porphyrins (2-Pt, 3-Pt) were not obtained because they did not readily dissolve in any solvents. The oxidation potentials of platinum bicycloporphyrins (4-Pt, 5-Pt, 6-Pt) were determined by cyclic voltammetry. The first oxidation potentials increased substantially (4-Pt: Eox1/2(1) = 0.515 V; 5-Pt: Eox1/2(1) = 0.609 V; 6-Pt: Eox1/2(1) = 0.658 V vs Ag/AgNO3, 0.1 M TBAP in PhCN, Fc = +0.076 V) compared with freebase CP (1) (Eox1/2(1) = +0.287 V, Eox1/2(2) = +0.699 V). The increase of the first oxidation potentials is not only the effect of the r–p conjugation, but also that of platinum coordination since 4-Pt also exhibited the increase of the oxidation potential compared to the freebase form.15 The oxidation potentials of the p-extended platinum porphyrins (1-Pt, 2-Pt, 3-Pt) were not obtained because they did not readily dissolve in any solvents. We used solution-based fabrication to make an FET device with 4-Pt, which was then converted to 1-Pt. The FET device containing 1-Pt was fabricated as follows.16 The source and drain electrodes were formed on a 300-nm-thick layer of thermally grown SiO2 on a Sb-doped n-type Si substrate (capacitance = 11.5 nF cm 2) by photolithography of Au (90 nm)/Cr (10 nm) layers. The standard channel length and width were 10 and 100 lm, respectively. The channels were spin coated with a 0.7 wt % CHCl3 solution of 4-Pt. The film was converted into 1-Pt by heating at 210 °C for 20 min. The devices were fabricated under a dry N2 atmosphere. The
S. Ito et al. / Tetrahedron Letters 56 (2015) 7043–7045
7045
Figure 2. UV–vis spectra of (a) 4-Pt (red) in CHCl3; (b) 1-Pt (green) in pyridine.
devices based on 1-Pt showed FET characteristics (10 lm: l = 2.3 10 3 cm2/V s, 100 lm: l = 4.9 10 4 cm2/V s). Conclusions We have prepared p-extended platinum porphyrins via bicycloporphyrins with [Pt4(OAc)82HOAc] or followed by the retro Diels– Alder reaction. Our method requires milder conditions than established methods and should assist in developing new functional organic materials that contain porphyrin units.
9. 10.
11.
Acknowledgments
12.
This work was partially supported by Cooperative Research Program of ‘Network Joint Research Center for Materials and Devices’ (No. 2013A15: to S.I.) and the Takahashi Industrial and Economic Research Foundation (No. 150: to S.I.). We would also like to thank Dr. Saika Otsubo (Mitsubishi Chemical Group, Science and Technology Research Center, Inc.) for fabricating and testing the FET devices and Mr. Makoto Roppongi (the Collaboration Center for Research and Development of Utsunomiya University) and Mr. Tomokichi Onoda (Shimamura Tech. Co.: Preparative HPLC Systems) for helping in experiments.
13.
References and notes 1. Borek, G.; Hanson, K.; Djurovich, P. I.; Thompson, M. E.; Aznavour, K.; Bau, R.; Sun, Y.; Forrest, S. R.; Brooks, J.; Michalski, L.; Brown, J. Angew. Chem., Int. Ed. 2007, 46, 1109–1112. 2. Papkovskii, D. B.; Savitskii, A. P.; Yaropolov, A. I.; Ponomarev, G. V.; Rumyantseva, V. D.; Mironov, A. F. Biomed. Sci. 1991, 2, 63–67. 3. Minari, T.; Seto, M.; Nemoto, T.; Isoda, S.; Tsukagoshi, K.; Aoyagi, Y. Appl. Phys. Lett. 2007, 91, 123501; Perez, M. D.; Borek, C.; Forrest, S. R.; Thompson, M. E. J. Am. Chem. Soc. 2009, 131, 9281–9286. 4. Noh, Y.; Lee, C.; Kim, J. J. Chem. Phys. 2003, 118, 2853–2864. 5. The Porphyrin HandbookInorganic, Organometallic and Coordination Chemistry; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: New York, 2000; Vol. 3, p 26. Chapter 15. 6. Sommer, J. R.; Shelton, A. H.; Parthasarathy, A.; Ghiviriga, I.; Reynolds, J. R.; Schanze, K. S. Chem. Mater. 2011, 23, 5296–5304. 7. Ito, S.; Murashima, T.; Uno, H.; Ono, N. Chem. Commun. 1998, 1661–1662; Ito, S.; Ochi, N.; Murashima, T.; Uno, H.; Ono, N. Chem. Commun. 2000, 893–894; Yamada, H.; Kuzuhara, D.; Takahashi, T.; Shimizu, Y.; Uota, K.; Okujima, T.; Uno, H.; Ono, N. Org. Lett. 2008, 10, 2947–2950. 8. Ito, S.; Phong, L.-T.; Komatsu, T.; Igarashi, N.; Otsubo, S.; Sakai, Y.; Ohno, A.; Aramaki, S.; Tanaka, Y.; Uno, H.; Oba, T.; Hiratani, K. Eur. J. Org. Chem. 2009, 31,
14.
15. 16.
5373–5382; Ito, S.; Terada, N.; Seino, K.; Makihata, D.; Sasaki, A.; Oba, T. Tetrahedron Lett. 2013, 54, 5916–5919. Buchler, J. W. In Porphyrins and Metalloporphyrins; Smith, K. M., Ed.; Elsevier: Amsterdam, 1975; p 157. Procedure for 5-Pt [Method A]: AcONa (50.0 mg, 608 lmol) was added to a suspension of bicycloporphyrin (5) (NCP: 5.00 mg, 6.08 lmol) and PtCl2 in AcOH (20 ml) and the mixture was refluxed for 24 h under Ar. The reaction was quenched with water and diluted with CHCl3. The organic layer was washed with saturated NaHCO3 aq (4), water (2) and brine (1), and dried over anhydrous Na2SO4. The solvent was removed and the reaction mixture was purified by column chromatography on silica gel 60 N (eluent CHCl3) followed by precipitation from methanol to give 2.40 mg (39%) of bicycloporphyrin platinum (5-Pt) as a red powder. Ito, S.; Ito, T.; Makihata, D.; Ishii, Y.; Saito, Y.; Oba, T. Tetrahedron Lett. 2014, 55, 4390–4394. Basato, M.; Biffis, A.; Martinati, G.; Tubaro, C.; Venzo, A.; Ganis, P.; Benetollo, F. Inorg. Chim. Acta 2003, 355, 299–403. General procedure for 4-Pt [Method B]: AcONa (0.140 g, 0.16 mol)/MeOH (10 ml) solution was added to a solution of bicycloporphyrin (1) (CP: 0.10 g, 0.16 mmol) and [Pt4(OAc)82AcOH] (250 mg, 0.18 mmol) in CHCl3 (130 ml) and the mixture was stirred at 60 °C for 48 h under Ar. The reaction was quenched with water and diluted with CHCl3. The organic layer was washed with water (2) and brine (1), and dried over anhydrous Na2SO4. The solvent was removed and the reaction mixture was purified by column chromatography on silica gel 60 N (eluent CHCl3) followed by precipitation from methanol to give 32.3 mg (25%) of bicycloporphyrin platinum (4-Pt) as a red powder. Selected experimental data for 4-Pt: Red powder, mp >200 °C (dec); 1H NMR (CDCl3, 500 MHz): d = 10.27 (s, 4H), 7.11 (s, 8H), 5.66 (s, 8H), 2.18 (m, 8H) ppm; UV–vis (CHCl3), kmax (log e): 382 (5.46), 498 (4.08), 532 (4.52) nm; MALDI-TOF (m/z) 817.61 (M+); calcd for C44H36N4Pt7/4CHCl39/4H2O. C, 53.37; H, 5.30; N, 4.55. Found: C, 53.91; H, 5.45; N, 4.22. For 5-Pt: Red powder, mp >280 °C (dec); 1H NMR (CDCl3, 500 MHz): d = 10.41 (s, 4H), 7.76 (s, 8H), 7.22 (s, 8H), 6.07 (m, 8H), 2.38–2.29 (m, 8H) ppm; UV–vis (CHCl3), kmax (log e): 384 (5.50), 499 (4.10), 532 (4.55) nm; MALDI-TOF (m/z) 1061.43 (M+); calcd for C60H44N4Pt1/ 2CHCl32H2O. C, 65.36; H, 4.40; N, 5.04. Found: C, 65.04; H, 4.42; N, 4.57. For 6-Pt: Red powder, mp >280 °C (dec); 1H NMR (CDCl3, 500 MHz): d = 10.48 (s, 4H), 8.21 (m, 8H), 7.88 (m, 8H), 7.44 (m, 8H), 6.21 (s, 8H), 2.51 (m, 8H), 2.39 (m, 8H) ppm; UV–vis (CHCl3), kmax (log e): 386 (5.36), 499 (4.01), 532 (4.43) nm; MALDI-TOF (m/z) 1215.73 (M+); calcd for C76H52N4Pt5/4CHCl39C2H5OH. C, 64.26; H, 6.07; N, 3.15. Found: C, 64.59; H, 6.40; N, 6.05. General procedure for 1-Pt: Bicycloporphyrin platinum (4-Pt) was heated in a glass tube oven under vacuum at 220 °C for 1 h to give corresponding tetrabenzoporphyrin platinum (1-Pt) in 100% yield. Selected experimental data for 1-Pt: Green powder, mp >200 °C; UV–vis (CHCl3), kmax (log e): 396 (4.99), 542 (4.03), 596 (5.03) nm; MALDI-TOF (m/z) 704.13 (M+); calcd for C36H20N4PtH2O. C, 59.92; H, 3.07; N, 7.76. Found: C, 60.22; H, 2.99; N, 8.01. For 2-Pt: Green powder, mp >200 °C; MALDI-TOF (m/z) 903.18 (M+); calcd for C52H28N4Pt3/2H2O. C, 67.09; H, 3.36; N, 6.02. Found: C, 67.32; H, 3.76; N, 5.89. For 3-Pt: Green powder, mp >200 °C; MALDI-TOF (m/z) 1103.20 (M+); calcd for C68H36N4Pt27/2H2O. C, 60.62; H, 4.71; N, 4.16. Found: C, 60.64; H, 5.07; N, 4.21. Ito, S.; Watanabe, H.; Uno, H.; Murashima, T.; Ono, N.; Tsai, Y.-C.; Compton, R. G. Tetrahedron Lett. 2001, 42, 707–710. Aramaki, S.; Sakai, Y.; Ono, N. Appl. Phys. Lett. 2004, 84, 2085.