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Synthesis, complexation, and mesomorphism of novel calixarene-linked discotic triphenylene based on click chemistry
Tetrahedron Letters 55 (2014) 252–255
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Synthesis, complexation, and mesomorphism of novel calixarene-linked discotic triphenylene based on click chemistry Biqiong Hong a,b, Fafu Yang a,c,⇑, Hongyu Guo a, Ziyu Jiao a a
College of Chemistry and Chemical Engineering, Fujian Normal University, Fuzhou 350007, PR China Command Academy of Fuzhou, The Chinese People’s Armed Police Force, Fuzhou 350002, PR China c Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, PR China b
a r t i c l e
i n f o
Article history: Received 26 August 2013 Revised 28 October 2013 Accepted 5 November 2013 Available online 13 November 2013 Keywords: Triphenylene Calixarene Mesophase Synthesis Complexation
a b s t r a c t The novel calixarene-linked discotic triphenylene 5a and 5b were synthesized in good yields via click chemistry. Structural and conformational characterization of new compounds had been achieved by NMR, MS, and elemental analysis. Their liquid crystalline behaviors before and after complexation were studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction. The neat compounds 5a and 5b showed mesophase but the complexes of 5a and 5b with metallic salts exhibited no liquid crystal behaviors. Ó 2013 Elsevier Ltd. All rights reserved.
Triphenylene derivatives with long alkyl chains have been extensively studied as one of the most well-known discotic and columnar liquid crystals. They exhibit various potential applications in the fields of organic light-emitting diodes, organic field-effect transistors, organic photovoltaic cells, gas sensors, photocopying machines, etc.1–6 Up to now, many triphenylene liquid crystals have been reported, such as hydrogen-bond stabilized triphenylene columns,7,8 polymers or oligomers of triphenylene,9–12 dendrimers of triphenylene,13,14 and nanoparticles of triphenylene.15,16 Recently, significant research attention is paid to the macrocycle-modified triphenylene dimers. In 2010, Cammidge reported the first conjugated macrocycle-based and crown ether macrocycle-based triphenylene dimers with interesting mesomorphic properties.17,18 Peng and Laschat, independently described the syntheses and properties of some similar macrocycle-based dimers.19,20 Their results indicate that the mesomorphic properties are controlled by the complexation behaviors of macrocycle units. Lately, we reported the first example of calixarene-linked triphenylene dimers that exhibit interesting mesomorphic behavior with either calixarenes bowlic columns or triphenylene columns as the core.21–23 Moreover, some of them possess interesting ion complexation-induced mesomorphic conversion between two columnar phases. These literatures also suggest that the different complexation behaviors of macrocycle unit give rise to different mesomorphic properties. However,
⇑ Corresponding author. Tel./fax: +86 591 83465225. E-mail address: [email protected] (F. Yang). 0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tetlet.2013.11.008
the syntheses of macrocycle-modified triphenylene and the relationship between the complexation and the mesomorphic properties are much less well-known. Click chemistry, developed by Meldal and Sharpless,24–28 is extensively applied in the areas of biological, materials, medicinal chemistry, etc. This chemistry involves Cu(I)-catalyzed 1,3-dipolar cycloaddition of an azide and a terminal alkyne. Recently, there are attempts of using click chemistry to construct the supramolecular receptors, such as calixarene derivatives, based on their complexation capability with various ions due to the hydrogen bond and dipole–dipole interactions of the 1,4-disubstituted 1,2,3-triazole ring.29–35 Theoretically, if the 1,2,3-triazole ring was introduced in calixarene–triphenylene liquid crystal by click chemistry, the 1,2,3-triazole ring would produce special influence on mesomorphic property based on its interesting complexation ability. In this Letter, we wish to describe for the first time the design and syntheses of the first calixarene-linked triphenylene dimers using click chemistry. Interestingly, complexation of the 1,2,3-triazole ring with metal ions produces non-mesomorphic behaviors compared with its native counterparts. Scheme 1 shows the synthetic route of the novel calixarenelinked triphenylene dimers based on click chemistry. According to the literature methods,36–38 the x-bromo-substituted triphenylenes 2a and 2b were prepared by reacting monohydroxytriphenylene 1 with excess 1,6-dibromohexane or 1,10-dibromodecane under K2CO3/MeCN system in 80% yield. Subsequently, the triphenylene derivatives 3a or 3b with the azide group were obtained by the
253
B. Hong et al. / Tetrahedron Letters 55 (2014) 252–255 RO RO
RO
OR Br-(CH2)n-Br
NaN3
K2CO3, MeCN
O (CH2)n-N3
RO O (CH2)n-Br
RO
OH
RO
OR
OR
OR
RO
RO
1 R= -C5H11
OR RO 2a ( n = 6 ), 2b ( n = 10 )
OR
3a ( n = 6 ), 3b ( n = 10 ) OR
OR OR RO
OR
RO
OR
RO
But
OR RO O
CuSO4 sodium ascorbate
* K2CO3/MeCN
*
O
3a or 3b
OH Bu
N N O
4
But
N
N
But
But But
t
O
n
OH OH
n
O
Br
N N OH OH
But But
O
But
5a ( n = 6 ), 5b ( n = 10 ) Scheme 1. The synthesis of target compounds 5a and 5b.
nucleophilic substitution reaction of 2a or 2b with NaN3 in DMF solution in quantitative yield. Calix[4]arene derivatives with alkynyl groups 4 were synthesized in 80% yield by reacting calix[4]arene with bromopropyne.39 Finally, the click reaction between compound 4 and 2a or 2b in DMF at 90 °C in the presence of copper(II) sulfate and sodium ascorbate as catalyst produced the target compounds 5a and 5b in 75% and 78% yields, respectively.40 The structures and conformations of novel calixarene-linked triphenylenes dimers 5a and 5b were studied by element analysis, ESI-MS, and 1H NMR spectra. Their ESI-MS spectra showed corresponding molecular ion peaks at 2325.1 and 2435.4, respectively. All the protons of compounds 5a and 5b were assigned well in their 1H NMR spectra. Their NMR spectra exhibited two singlets (1:1) for the tert-butyl groups, one pair of doublets (1:1) for the methylene bridges and two singlets (1:1) for ArH, which confirm the cone conformation of the calix[4]arene units. The mesomorphic behaviors of compounds 5a and 5b were studied by differential scanning calorimetry (DSC) that is shown
cooling
heat flow (KJ / mmol) exo
3 2 1
Cr
LC
Iso
5b
Cr
LC
Iso
5a
in Figure 1. Both compounds 5a and 5b possessed two phase transitions upon second heating and cooling. Compound 5a showed two phase transfer temperatures at 78.5 °C and 123.5 °C in the second heating process and two reverse processes at 117.8 °C and 63.8 °C in the cooling process. Similarly, compound 5b exhibited two phase transfer temperatures at 57.1 °C and 133.2 °C in the second heating scan and two reverse processes at 121.3 °C and 50.2 °C upon cooling. The DSC data suggest that the mesophase exists on the melting process and the crystal phase-mesophase-isotropic phase on the heating process. Also, it can be seen that compound 5b exhibits a wider mosomorphic temperature range than compound 5a, which might be attributed to the influence of the longer bridging chain of compound 5b. Based on the DSC results, the phase textures of the mesophase of compounds 5a and 5b were further investigated using polarized optical microscopy (POM). Figure 2 shows the mesomorphic textures at the corresponding temperatures and the obvious fan-like columnar-shaped textures were observed. These textures were similar to the known textures for columnar phase of triphenylene derivatives.41–46 Also, X-ray diffraction (XRD) was used to study the mesomorphic stacking behavior of compounds 5a and 5b (Fig. 3). Typical peaks of columnar phase of triphenylene liquid crystals (2h = 5 °C, 16–22 °C and 24 °C approximately) were observed for compounds 5a and
0 -1
Cr
-2
Cr
Iso
LC
5a
LC
-3
Iso
5b
second heating
-4 20
40
60
80
100
120
140
160
180
Temperature oC Figure 1. The DSC traces of 5a and 5b on second heating and cooling (scan rate 10 °C min 1).
Figure 2. Fan-like textures of 5a and 5b obtained with polarized optical microscopy on cooling at 90 °C (400).
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B. Hong et al. / Tetrahedron Letters 55 (2014) 252–255 2
5b+AgSCN
Intensity
5a
5b
heat flow (KJ / mmol) exo
1
5b+NaCl 0
5b+NaSCN -1
5a+NaSCN 5a+AgSCN
-2
-3
5a+NaCl
second heating
-4
10
20
30
degrees
20
40
60
80
100
120
140
160
180
Temperature oC
Figure 3. XRD traces of 5a and 5b measured at 90 °C. Figure 5. The DSC traces of complexes of 5a and 5b with metallic salts on second heating (scan rate 10 °C min 1).
5b.41–46 The reflections at about 2h = 5 °C correspond to the distances of 17.6 Å, which agrees reasonably well with the diameter of the triphenylene group. The reflections at 2h = 16–22 °C (4.1–5.5 Å broad halo), 21.5 °C(4.12 Å), and 24 °C (3.7 Å) are assigned to the average distances of the molten alkyl chains, the bridging chain, and the intracolumnar order, respectively. Moreover, it is interesting that no diffraction peak of calixarene units was observed.47–51 These XRD results suggest that the triphenylene units in 5a and 5b show classical columnar molecular stacking but the calixarene units exhibit no ordered molecular stacking. Referring to the previous molecular stacking analysis of similar structural liquid crystals,21–23 we propose that compounds 5a and 5b possess the triphenylene column with calixarene units on ancillary lateral sides as shown in Figure 4b. In order to study the influence of the complexation with metal ions on the mesomorphic properties, the complexes 5a and 5b with several metallic salts (including hard and soft cations or anions) were prepared by the procedure reported by Pedersen and modified by Laschat.52,53 Typically, a solution of the host (1 equiv) in CH2Cl2 was added to a solution of the respective metallic salt (1.5 equiv) in MeOH. The resulting slurry was vigorously stirred overnight. After evaporation of the solvents, the residue was taken up in boiling CH2Cl2 and the solution was filtered. The filtrate was concentrated and dried under vacuum to afford the respective complex in quantitative yields. A 1:1 M ratio of host:guest was confirmed by elemental analysis. The ESI-MS spectra of complexes of compounds 5a and 5b with NaSCN were also studied and the results showed that the corresponding molecular ion peaks with a 1:1 M ratio of host:guest were observed at 2347.2 and 2458.8, respectively. The DSC results upon the second heating of these metal complexes are plotted in Figure 5. All complexes show only one peak of phase transition, which indicates no mesophase exists on heating. Moreover, polarized optical microscopy shows phase textures of only solid phase-isotropic phase processes. Also, the melting points of these complexes are higher than that of neat 5a and 5b. All these results might be explained that these
(a)calixarenes bowlic column with two triphenylene units as ancillary lateral columns
(b) triphenylene column with calixarene units on ancillary lateral side
Figure 4. Two kinds of schematic representation of the columnar layered molecular arrangement for triads of triphenylene-calixarene–triphenylene.21–23
complexes of 5a and 5b with ions produced not only the more rigid structures because of the action between host and guest reducing the flexibility of the binding cavity, but also the strong intermolecular action due to the existence of cations and anions in complexes, which causes the disappearance of the mesomorphic properties and give rise to the higher melting points. In conclusion, we have demonstrated the design and synthesis of novel calixarene-linked discotic triphenylene 5a and 5b in good yields via click chemistry. Their structures and conformations were characterized by NMR, MS, and elemental analysis. Their liquid crystalline behaviors before and after complexation with metal ions were studied by DSC, POM, and XRD. Neat compounds 5a and 5b showed mesophase with triphenylene column as the core, while complexes of 5a and 5b with metal salts exhibited no mesophase that was observed for the first time. Acknowledgments Financial support from the National Natural Science Foundation of China (No: 20402002), Fujian Natural Science Foundation of China (No. 2009J01019), the Program for Innovative Research Team in Science and Technology in Fujian Province University and Program for Excellent young researchers in University of Fujian Province (JA10056) were greatly acknowledged. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2013. 11.008. References and notes 1. Sergeyev, S.; Pisula, W.; Geerts, Y. H. Chem. Soc. Rev. 2007, 36, 1902–1929. 2. Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Hagele, C.; Scalia, G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M. Angew. Chem., Int. Ed. 2007, 46, 4832–4887. 3. Kato, T.; Mizoshita, N.; Kishimoto, K. Angew. Chem., Int. Ed. 2006, 45, 38–68. 4. Kumar, S. Chem. Soc. Rev. 2006, 35, 83–109. 5. Kumar, S. Liq. Cryst. 2005, 32, 1089–1113. 6. Kumar, S. Liq. Cryst. 2004, 31, 1037–1059. 7. Miao, J.; Zhu, L. Chem. Mater. 2010, 22, 197–206. 8. Paraschiv, I.; Giesbers, M.; Lagen, B.; Grozema, F.; Abellon, R.; Siebbeles, L.; Marcelis, A.; Zuilhof, H.; Sudhölter, E. Chem. Mater. 2006, 18, 968–974. 9. Wang, T.; Yan, D.; Zhou, E.; Karthaus, O.; Ringsdorf, H. Polymer 1998, 39, 4509– 4513. 10. Boden, N.; Borner, R. C.; Bushby, R. J.; Cammidge, A. N.; Jesudason, M. V. Liq. Cryst. 2006, 33, 11–12.
B. Hong et al. / Tetrahedron Letters 55 (2014) 252–255 11. Boden, N.; Bushby, R. J.; Liu, Q. Y.; Lozman, O. R. J. Mater. Chem. 2001, 11, 1612– 1617. 12. Pal, S. K.; Kumar, S. Liq. Cryst. 2008, 35, 381–384. 13. Mekenna, M. D.; Barbera, J.; Marcos, M.; Serrano, J. L. J. Am. Chem. Soc. 2005, 127, 619–625. 14. Zelcer, A.; Donnio, B.; Bourgogne, C.; Cukiernik, F. D.; Guillon, D. Chem. Mater. 2007, 19, 1992–2006. 15. Bisoyi, H. K.; Kumar, S. J. Mater. Chem. 2008, 18, 3032–3039. 16. Kumar, S.; Pal, S. K.; Kumar, P. S.; Lakshminarayanan, V. Soft Matter 2007, 3, 896–900. 17. Li, J.; He, Z.; Gopee, H.; Cammidge, A. N. Org. Lett. 2010, 12, 472–475. 18. Zhang, L.; Gopee, H.; Hughes, D.; Cammidge, A. N. Chem. Commun. 2010, 4255– 4257. 19. Wang, D.; Hsu, J. F.; Bagui, M.; Dusevich, V.; Wang, Y.; liu, Y.; Holder, A.; Peng, Z. Tetrahedron Lett. 2009, 50, 2147–2149. 20. Kaller, M.; Deck, C.; Meister, A.; Hause, G.; Baro, A.; Laschat, S. Chem. Eur. J. 2010, 16, 6326–6337. 21. Yang, F. F.; Guo, H. Y.; Xie, J. W.; Lin, J. R. Eur. J. Org. Chem. 2011, 26, 5141–5145. 22. Yang, F. F.; Xu, B. T.; Guo, H. Y.; Xie, J. W. Tetrahedron Lett. 2012, 53, 1598–1602. 23. Yang, F. F.; Bai, X. Y.; Li, C. C.; Guo, H. Y. Tetrahedron Lett. 2013, 54, 409–413. 24. Tornoe, C. M.; Christensen, C. M.; Meldal, J. J. Org. Chem. 2002, 67, 3057–3064. 25. Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 41, 2596–2599. 26. Moses, J. E.; Moorhouse, A. D. Chem. Soc. Rev. 2007, 36, 1249–1262. 27. Fournier, D.; Hoogenboom, R.; Schubert, U. S. Chem. Soc. Rev. 2007, 36, 1369– 1380. 28. Wang, Q.; Chan, T. R.; Hilgraf, R.; Fokin, V. V.; Sharpless, K. B.; Finn, M. G. J. Am. Chem. Soc. 2003, 125, 3192–3193. 29. Kellermann, M.; Bauer, W.; Hirsch, A.; Schade, B.; Ludwig, K.; Böttcher, C. Angew. Chem., Int. Ed. 2004, 43, 2959–2962. 30. Lee, M.; Lee, S. J.; Jiang, L. H. J. Am. Chem. Soc. 2004, 126, 12724–12725. 31. Chang, K. C.; Su, I. H.; Senthilvelan, A.; Chung, W. S. Org. Lett. 2007, 9, 3363– 3366. 32. Chang, K. C. Su.; Su, I. H.; Lee, G. H.; Chung, W. S. Tetrahedron Lett. 2007, 48, 7274–7278. 33. Park, S. Y.; Yoon, J. H.; Hong, C. S.; Souane, R.; Kim, J. S.; Matthews, S. E.; Vicens, J. J. Org. Chem. 2008, 73, 8212–8218. 34. Colasson, B.; Save, M.; Milko, P.; Roithová, J.; Schröder, D.; Reinaud, O. Org. Lett. 2007, 9, 4987–4990. 35. Colasson, B.; Poul, N. L.; Mest, Y. L.; Reinaud, O. J. Am. Chem. Soc. 2010, 132, 4393–4398. 36. Kumar, S.; Manickam, M. Synthesis 1998, 12, 1119–1125.
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37. Bisoyi, H. K.; Kumar, S. Tetrahedron Lett. 2008, 49, 3628–3631. 38. Kumar, S.; Pal, S. K. Tetrahedron Lett. 2005, 46, 4127–4130. 39. Francisco, G. C. F.; Joaquín, I. G.; Fernando, H. M.; Francisco, P. B.; Jose, A. C. A.; Eduardo, S. V.; Francisco, S. G. Org. Lett. 2000, 2, 2499–2502. 40. Synthesis of compound 5a and 5b: Compound 3a (160 mg, 0.2 mmol) or 3b (170 mg, 0.2 mmol), CuSO45H2O (62 mg, 0.25 mmol) and sodium ascorbate (100 mg, 0.5 mmol) were added to a solution of 4 (72 mg, 0.1 mmol) in DMF (10 mL). The mixture was heated at 90 °C for 10 h, and then diluted with CHCl3 (30 mL) and washed with water (2 20 mL). The organic phase was dried over MgSO4, filtered and the solvent removed under reduced pressure. The residue was recrystallized from CHCl3/MeOH to afford 5a and 5b as white solid in yield of 81% and 84%, respectively. Compound 5a: 1H NMR (400 MHz, CDCl3) d ppm: 0.98 (t, 30H, CH2CH3), 1.01 (s, 18H, C(CH3)3), 1.25 (s, 18H, C(CH3)3), 1.33–1.96 (m, 76H, CH2), 3.28 (d, 4H, J = 13.2 Hz, ArCH2Ar), 4.13–4.40(m, 32H, OCH2, NCH2 and ArCH2Ar), 5.18 (br s, 4H, OCH2-trazole), 6.86 (s, 4H, ArH), 7.03 (s, 4H, ArH), 7.05 (s, 2H, CH), 7.82 (br s, 12H, TpH), 8.05 (s, 2H, OH); MS m/z (%): 2325.1 (M+, 100). Anal. Calcd for C148H206N6O16: C, 76.46; H, 8.92; N 3.60. Found C, 76.49; H, 8.96; N, 3.56. Compound 5b: 1H NMR (400 MHz, CDCl3) d ppm: 0.98 (t, 30H, CH2CH3), 1.00 (s, 18H, C(CH3)3), 1.22 (s, 18H, C(CH3)3), 1.37– 1.97 (m, 92H, CH2), 3.29 (d, 4H, J = 12.8 Hz, ArCH2Ar), 4.15–4.35(m, 32H, OCH2, NCH2 and ArCH2Ar), 5.20 (s, 4H, OCH2-trazole), 6.85 (s, 4H, ArH), 7.03 (s, 4H, ArH), 7.57 (s, 2H, CH), 7.83 (br s, 12H, TpH), 8.01 (s, 2H, OH); MS m/z (%): 2435.4 (M+, 100). Anal. Calcd for C156H222N6O16: C, 76.87; H, 9.19; N, 3.44. Found C, 76.85; H, 9.22; N, 3.41. 41. Prasad, S. K.; Rao, A. S.; Chandrasekhar, S.; Kumar, S. Mol. Cryst. Liq. Cryst. 2003, 396, 121–139. 42. Wan, W.; Wang, P. Y.; Jiang, H. Z.; Hao, J. Mol. Cryst. Liq. Cryst. 2008, 482, 42–46. 43. Wan, W.; Monobe, H.; Tanaka, Y.; Shimizu, Y. Liq. Cryst. 2003, 30, 571–578. 44. Ba, C.; Shen, Z.; Gu, H.; Guo, G.; Xie, P.; Zhang, R. Liq. Cryst. 2003, 30, 391–397. 45. Paraschiv, J.; Tomkinson, A.; Giesbers, M.; Sudhölter, E.; Zuilhof, H.; Marcelis, A. Liq. Cryst. 2007, 34, 1029–1038. 46. Zhao, B.; Liu, B.; Png, R. Q.; Zhang, K.; Lim, K. A.; Luo, J.; Shao, J.; Ho, P.; Chi, C.; Wu, J. Chem. Mater. 2010, 22, 435–449. 47. Yonetake, K.; Nakayama, T.; Ueda, M. J. Mater. Chem. 2001, 11, 761–767. 48. Komori, T.; Shinkai, S. Chem. Lett. 1993, 8, 1455–1458. 49. Xu, B.; Swager, T. M. J. Am. Chem. Soc. 1993, 115, 1159–1160. 50. Xu, B.; Swager, T. M. J. Am. Chem. Soc. 1995, 117, 5011–5012. 51. Patel, R. V.; Panchal, J. G.; Rana, V. A.; Menon, S. K. J. Incl. Phenom. Macrocycl. Chem. 2010, 66, 285–295. 52. Pedersen, C. J. J. Am. Chem. Soc. 1967, 89, 7017–7036. 53. Kaller, M.; Tussetschl ger, S.; Fischer, P.; Deck, C.; Baro, A.; Giesselmann, F.; Laschat, S. Chem. Eur. J. 2009, 15, 9530–9542.
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Synthesis, complexation, and mesomorphism of novel calixarene-linked discotic triphenylene based on click chemistry Biqiong Hong a,b, Fafu Yang a,c,⇑, Hongyu Guo a, Ziyu Jiao a a
College of Chemistry and Chemical Engineering, Fujian Normal University, Fuzhou 350007, PR China Command Academy of Fuzhou, The Chinese People’s Armed Police Force, Fuzhou 350002, PR China c Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, PR China b
a r t i c l e
i n f o
Article history: Received 26 August 2013 Revised 28 October 2013 Accepted 5 November 2013 Available online 13 November 2013 Keywords: Triphenylene Calixarene Mesophase Synthesis Complexation
a b s t r a c t The novel calixarene-linked discotic triphenylene 5a and 5b were synthesized in good yields via click chemistry. Structural and conformational characterization of new compounds had been achieved by NMR, MS, and elemental analysis. Their liquid crystalline behaviors before and after complexation were studied by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction. The neat compounds 5a and 5b showed mesophase but the complexes of 5a and 5b with metallic salts exhibited no liquid crystal behaviors. Ó 2013 Elsevier Ltd. All rights reserved.
Triphenylene derivatives with long alkyl chains have been extensively studied as one of the most well-known discotic and columnar liquid crystals. They exhibit various potential applications in the fields of organic light-emitting diodes, organic field-effect transistors, organic photovoltaic cells, gas sensors, photocopying machines, etc.1–6 Up to now, many triphenylene liquid crystals have been reported, such as hydrogen-bond stabilized triphenylene columns,7,8 polymers or oligomers of triphenylene,9–12 dendrimers of triphenylene,13,14 and nanoparticles of triphenylene.15,16 Recently, significant research attention is paid to the macrocycle-modified triphenylene dimers. In 2010, Cammidge reported the first conjugated macrocycle-based and crown ether macrocycle-based triphenylene dimers with interesting mesomorphic properties.17,18 Peng and Laschat, independently described the syntheses and properties of some similar macrocycle-based dimers.19,20 Their results indicate that the mesomorphic properties are controlled by the complexation behaviors of macrocycle units. Lately, we reported the first example of calixarene-linked triphenylene dimers that exhibit interesting mesomorphic behavior with either calixarenes bowlic columns or triphenylene columns as the core.21–23 Moreover, some of them possess interesting ion complexation-induced mesomorphic conversion between two columnar phases. These literatures also suggest that the different complexation behaviors of macrocycle unit give rise to different mesomorphic properties. However,
⇑ Corresponding author. Tel./fax: +86 591 83465225. E-mail address: [email protected] (F. Yang). 0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.tetlet.2013.11.008
the syntheses of macrocycle-modified triphenylene and the relationship between the complexation and the mesomorphic properties are much less well-known. Click chemistry, developed by Meldal and Sharpless,24–28 is extensively applied in the areas of biological, materials, medicinal chemistry, etc. This chemistry involves Cu(I)-catalyzed 1,3-dipolar cycloaddition of an azide and a terminal alkyne. Recently, there are attempts of using click chemistry to construct the supramolecular receptors, such as calixarene derivatives, based on their complexation capability with various ions due to the hydrogen bond and dipole–dipole interactions of the 1,4-disubstituted 1,2,3-triazole ring.29–35 Theoretically, if the 1,2,3-triazole ring was introduced in calixarene–triphenylene liquid crystal by click chemistry, the 1,2,3-triazole ring would produce special influence on mesomorphic property based on its interesting complexation ability. In this Letter, we wish to describe for the first time the design and syntheses of the first calixarene-linked triphenylene dimers using click chemistry. Interestingly, complexation of the 1,2,3-triazole ring with metal ions produces non-mesomorphic behaviors compared with its native counterparts. Scheme 1 shows the synthetic route of the novel calixarenelinked triphenylene dimers based on click chemistry. According to the literature methods,36–38 the x-bromo-substituted triphenylenes 2a and 2b were prepared by reacting monohydroxytriphenylene 1 with excess 1,6-dibromohexane or 1,10-dibromodecane under K2CO3/MeCN system in 80% yield. Subsequently, the triphenylene derivatives 3a or 3b with the azide group were obtained by the
253
B. Hong et al. / Tetrahedron Letters 55 (2014) 252–255 RO RO
RO
OR Br-(CH2)n-Br
NaN3
K2CO3, MeCN
O (CH2)n-N3
RO O (CH2)n-Br
RO
OH
RO
OR
OR
OR
RO
RO
1 R= -C5H11
OR RO 2a ( n = 6 ), 2b ( n = 10 )
OR
3a ( n = 6 ), 3b ( n = 10 ) OR
OR OR RO
OR
RO
OR
RO
But
OR RO O
CuSO4 sodium ascorbate
* K2CO3/MeCN
*
O
3a or 3b
OH Bu
N N O
4
But
N
N
But
But But
t
O
n
OH OH
n
O
Br
N N OH OH
But But
O
But
5a ( n = 6 ), 5b ( n = 10 ) Scheme 1. The synthesis of target compounds 5a and 5b.
nucleophilic substitution reaction of 2a or 2b with NaN3 in DMF solution in quantitative yield. Calix[4]arene derivatives with alkynyl groups 4 were synthesized in 80% yield by reacting calix[4]arene with bromopropyne.39 Finally, the click reaction between compound 4 and 2a or 2b in DMF at 90 °C in the presence of copper(II) sulfate and sodium ascorbate as catalyst produced the target compounds 5a and 5b in 75% and 78% yields, respectively.40 The structures and conformations of novel calixarene-linked triphenylenes dimers 5a and 5b were studied by element analysis, ESI-MS, and 1H NMR spectra. Their ESI-MS spectra showed corresponding molecular ion peaks at 2325.1 and 2435.4, respectively. All the protons of compounds 5a and 5b were assigned well in their 1H NMR spectra. Their NMR spectra exhibited two singlets (1:1) for the tert-butyl groups, one pair of doublets (1:1) for the methylene bridges and two singlets (1:1) for ArH, which confirm the cone conformation of the calix[4]arene units. The mesomorphic behaviors of compounds 5a and 5b were studied by differential scanning calorimetry (DSC) that is shown
cooling
heat flow (KJ / mmol) exo
3 2 1
Cr
LC
Iso
5b
Cr
LC
Iso
5a
in Figure 1. Both compounds 5a and 5b possessed two phase transitions upon second heating and cooling. Compound 5a showed two phase transfer temperatures at 78.5 °C and 123.5 °C in the second heating process and two reverse processes at 117.8 °C and 63.8 °C in the cooling process. Similarly, compound 5b exhibited two phase transfer temperatures at 57.1 °C and 133.2 °C in the second heating scan and two reverse processes at 121.3 °C and 50.2 °C upon cooling. The DSC data suggest that the mesophase exists on the melting process and the crystal phase-mesophase-isotropic phase on the heating process. Also, it can be seen that compound 5b exhibits a wider mosomorphic temperature range than compound 5a, which might be attributed to the influence of the longer bridging chain of compound 5b. Based on the DSC results, the phase textures of the mesophase of compounds 5a and 5b were further investigated using polarized optical microscopy (POM). Figure 2 shows the mesomorphic textures at the corresponding temperatures and the obvious fan-like columnar-shaped textures were observed. These textures were similar to the known textures for columnar phase of triphenylene derivatives.41–46 Also, X-ray diffraction (XRD) was used to study the mesomorphic stacking behavior of compounds 5a and 5b (Fig. 3). Typical peaks of columnar phase of triphenylene liquid crystals (2h = 5 °C, 16–22 °C and 24 °C approximately) were observed for compounds 5a and
0 -1
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Figure 2. Fan-like textures of 5a and 5b obtained with polarized optical microscopy on cooling at 90 °C (400).
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Figure 3. XRD traces of 5a and 5b measured at 90 °C. Figure 5. The DSC traces of complexes of 5a and 5b with metallic salts on second heating (scan rate 10 °C min 1).
5b.41–46 The reflections at about 2h = 5 °C correspond to the distances of 17.6 Å, which agrees reasonably well with the diameter of the triphenylene group. The reflections at 2h = 16–22 °C (4.1–5.5 Å broad halo), 21.5 °C(4.12 Å), and 24 °C (3.7 Å) are assigned to the average distances of the molten alkyl chains, the bridging chain, and the intracolumnar order, respectively. Moreover, it is interesting that no diffraction peak of calixarene units was observed.47–51 These XRD results suggest that the triphenylene units in 5a and 5b show classical columnar molecular stacking but the calixarene units exhibit no ordered molecular stacking. Referring to the previous molecular stacking analysis of similar structural liquid crystals,21–23 we propose that compounds 5a and 5b possess the triphenylene column with calixarene units on ancillary lateral sides as shown in Figure 4b. In order to study the influence of the complexation with metal ions on the mesomorphic properties, the complexes 5a and 5b with several metallic salts (including hard and soft cations or anions) were prepared by the procedure reported by Pedersen and modified by Laschat.52,53 Typically, a solution of the host (1 equiv) in CH2Cl2 was added to a solution of the respective metallic salt (1.5 equiv) in MeOH. The resulting slurry was vigorously stirred overnight. After evaporation of the solvents, the residue was taken up in boiling CH2Cl2 and the solution was filtered. The filtrate was concentrated and dried under vacuum to afford the respective complex in quantitative yields. A 1:1 M ratio of host:guest was confirmed by elemental analysis. The ESI-MS spectra of complexes of compounds 5a and 5b with NaSCN were also studied and the results showed that the corresponding molecular ion peaks with a 1:1 M ratio of host:guest were observed at 2347.2 and 2458.8, respectively. The DSC results upon the second heating of these metal complexes are plotted in Figure 5. All complexes show only one peak of phase transition, which indicates no mesophase exists on heating. Moreover, polarized optical microscopy shows phase textures of only solid phase-isotropic phase processes. Also, the melting points of these complexes are higher than that of neat 5a and 5b. All these results might be explained that these
(a)calixarenes bowlic column with two triphenylene units as ancillary lateral columns
(b) triphenylene column with calixarene units on ancillary lateral side
Figure 4. Two kinds of schematic representation of the columnar layered molecular arrangement for triads of triphenylene-calixarene–triphenylene.21–23
complexes of 5a and 5b with ions produced not only the more rigid structures because of the action between host and guest reducing the flexibility of the binding cavity, but also the strong intermolecular action due to the existence of cations and anions in complexes, which causes the disappearance of the mesomorphic properties and give rise to the higher melting points. In conclusion, we have demonstrated the design and synthesis of novel calixarene-linked discotic triphenylene 5a and 5b in good yields via click chemistry. Their structures and conformations were characterized by NMR, MS, and elemental analysis. Their liquid crystalline behaviors before and after complexation with metal ions were studied by DSC, POM, and XRD. Neat compounds 5a and 5b showed mesophase with triphenylene column as the core, while complexes of 5a and 5b with metal salts exhibited no mesophase that was observed for the first time. Acknowledgments Financial support from the National Natural Science Foundation of China (No: 20402002), Fujian Natural Science Foundation of China (No. 2009J01019), the Program for Innovative Research Team in Science and Technology in Fujian Province University and Program for Excellent young researchers in University of Fujian Province (JA10056) were greatly acknowledged. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2013. 11.008. References and notes 1. Sergeyev, S.; Pisula, W.; Geerts, Y. H. Chem. Soc. Rev. 2007, 36, 1902–1929. 2. Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Hagele, C.; Scalia, G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M. Angew. Chem., Int. Ed. 2007, 46, 4832–4887. 3. Kato, T.; Mizoshita, N.; Kishimoto, K. Angew. Chem., Int. Ed. 2006, 45, 38–68. 4. Kumar, S. Chem. Soc. Rev. 2006, 35, 83–109. 5. Kumar, S. Liq. Cryst. 2005, 32, 1089–1113. 6. Kumar, S. Liq. Cryst. 2004, 31, 1037–1059. 7. Miao, J.; Zhu, L. Chem. Mater. 2010, 22, 197–206. 8. Paraschiv, I.; Giesbers, M.; Lagen, B.; Grozema, F.; Abellon, R.; Siebbeles, L.; Marcelis, A.; Zuilhof, H.; Sudhölter, E. Chem. Mater. 2006, 18, 968–974. 9. Wang, T.; Yan, D.; Zhou, E.; Karthaus, O.; Ringsdorf, H. Polymer 1998, 39, 4509– 4513. 10. Boden, N.; Borner, R. C.; Bushby, R. J.; Cammidge, A. N.; Jesudason, M. V. Liq. Cryst. 2006, 33, 11–12.
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