DOI: 10.1002/asia.201403028
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Polycycles
Tetrathio and Tetraseleno[8]circulenes: Synthesis, Structures, and Properties Xiaodong Xiong,[a] Chun-Lin Deng,[a] Boris F. Minaev,[c] Gleb V. Baryshnikov,[c] Xiao-Shui Peng,[a, b] and Henry N. C. Wong*[a, b]
applications as electronic materials. The antiaromatic nature of tetrathio[8]circulene and tetraselenium[8]circulene was studied by computational methods, and the NICS computational results reveal that the central eight-membered ring has highly antiaromatic character.
Abstract: Novel sulfur and selenium-bridged [8]circulenes were prepared from octabromotetraphenylene. Structures of these compounds were unambiguously confirmed by X-ray crystallographic analyses. Photophysical and electrochemical investigations of these [8]circulenes suggest their potential
Introduction In the family of polycyclic aromatic compounds, [n]circulenes are macrocyclic arenes produced by benzene rings being completely surrounded and fused around central n-sided polygons.[1] Only four members of this homologous series of compounds have been successfully prepared up to 2013: [4]circulene (quadrannulene),[2] [5]circulene (corannulene),[3] [6]circulene (coronene),[4] and [7]circulene (pleiadannulene).[5] The conspicuous geometric features of these circulenes change from a bow (quadrannulene and corannulene) through a plane (coronene) to a saddle (pleiadannulene). Recently, the synthesis of the parent [8]circulene 1 (in Figure 1 without side substituents for clarity) has been reported by Wu and coworkers.[6a] [8]Circulene 1 had been predicted previously to be aromatic but with nonplanar tub-shaped geometry belonging to D2d symmetry, and with alternating single and double bonds.[7] Computational studies are consistent with the newly prepared [8]circulene derivative 2, in which the saddle structure was unambiguously confirmed by an X-ray crystallographic study.[6b, c] By contrast,
Figure 1. Representative examples of [8]circulenes.
the corresponding tetraoxa[8]circulene 3 has been known for a long time, and was firstly prepared in 1968 by treatment of 1,4-benzoquinone with a strong acid. X-ray diffraction results suggest that its central eight-membered ring is constrained to adopt a planar structure.[8] Recently, a number of tetraoxa[8]circulene derivatives[9] and their planar analogs, such as tetracyclopenta[def,jkl,pqr,vwx]-tetraphenylene (TCT) 4,[10] octathio[8]circulene 5,[11] nitrogen atom containing diazadioxa[8]circulene 6,[12] and tetrathiotetraseleno[8]circulene[13] have been successfully prepared. Analyses of their experimental and computational data show that these planarized cyclooctatetraenes are antiaromatic.[12, 14] As antiaromatic compounds often display unique electrochemical and optical properties on the entire pconjugated systems, studies of the geometry and aromatic/antiaromatic properties of heterocyclic [8]circulene have inevitably attracted an increasing attention from many chemists.[15] Moreover, these [8]circulenes are potential candidates as DNA intercalators,[9b] liquid crystalline materials,[9c, h] stable cation-
[a] Dr. X. Xiong, C.-L. Deng, Dr. X.-S. Peng, Prof. Dr. H. N. C. Wong Department of Chemistry, State Key Laboratory of Synthetic Chemistry Center of Novel Functional Molecules, and Institute of Molecular Functional Materials The Chinese University of Hong Kong Shatin, New Territories, Hong Kong SAR (China) Fax: (+ 852) 26035315 E-mail: [email protected] [b] Dr. X.-S. Peng, Prof. Dr. H. N. C. Wong Shenzhen Center of Novel Functional Molecules Shenzhen Research Institute The Chinese University of Hong Kong No.10, Second Yuexing Road, Shenzhen 518507 (China) [c] Prof. Dr. B. F. Minaev, Dr. G. V. Baryshnikov Bohdan Khmelnytsky National University 18301, Cherkasy (Ukraine) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201403028. Chem. Asian J. 2014, 9, 1 – 8
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Full Paper radical salts,[7d] organic light-emitting diodes,[9f] and organic semiconductors.[13, 14b, 15h, i] Therefore, syntheses of [8]circulenes are always synthetically important. Experimentally, incorporation of triple bonds into eightmembered rings, annulation of small-membered rings, and fusion of rigid planar p-systems to tetraphenylenes could all make their central cyclooctatetraene rings planar.[8–12, 16] As a result of the planarity, considerable antiaromatic paratropicity could be detected.[14b, 15a, 17] In this field, Hçgberg,[8, 9a] Nishinaga,[14b] and Pittelkow[9e–g, 12] synthesized a class of planar antiaromatic cyclooctatetraenes by introducing heteroatom bridges. Very recently, we also reported the synthesis and studies of dioxo-, diaza-, dithio-, and diseleno-bridged partially planar tetraphenylenes.[18] Inspired by these encouraging results, we envisioned that the synthesis of tetraseleno[8]circulene 7 and tetrathio[8]circulene 8 could be achieved by insertion of selenium and sulfur bridges in the bay regions of tetraphenylene. Herein, we describe the first synthesis of [8]circulenes 7 and 8, as well as studies of their electrochemical, photophysical, and antiaromatic properties.
with NBS in trifluoroacetic acid to afford octabromide 10 in 58 % yield. Then 10 was treated with an excess of nBuLi, resulting in its complete lithiation. Addition of selenium powder in one portion to the resulting lithium salt led to the formation of the polyselenium tetraphenylene intermediate, which, when subjected to thermal deselenation with copper powder at 250 8C, afforded the desired [8]circulene 7 in 19 % yield (Scheme 1). In a similar strategy, [8]circulene 8 was obtained in an overall 15 % yield, starting also from octabromotetraphenylene 10. Structures of 7 and 8 were confirmed by X-ray crystallographic studies. In this manner, we have developed an effective method to construct these intriguing molecular architectures. As shown in Table 1, while X-ray crystallographic analyses indicate that tetraphenylene 9[19] and [8]circulene 7 are saddleshaped, [8]circulene 8 can be shown to possess a cyclic 8p electron central eight-membered ring in an essentially planar conformation. As regarding the inner angles of the central eight-membered ring, the average values in the crystal structures of 7 and 8 are found to be 134.2 and 134.98, respectively, which are larger than the inner angle of a regular tetraphenylene [viz. 9 (122.78)]. However, the average bent angles (a) of 7 and 8 are 4.08 and 0.18, respectively, which are substantially less than that of 9 (52.18). Consequently, the eight-membered ring of 7 is less puckered than that of tetraphenylene 9. As can
Results and Discussion In view of the possibility that it is difficult to directly lithiate octamethoxytetraphenylene 9[19] according to a known procedure,[20] we therefore utilized an indirect method by introducing eight bromine atoms to 9. Thus, 9 underwent bromination
Table 1. Selected structural data analysis of heterocyclic [8]circulenes.[a]! 9 X-ray
7 X-ray
8 Calcd. X-ray
Calcd.
Bond 1.39/ length[] 1.49/
1.49/ 1.45/
1.49/ 1.45/
1.47/ 1.43/
1.48/ 1.44/
1.42/ 1.88
1.42/ 1.72
1.42/ 1.74
r1/r2/r3/r4 1.40/– 1.42/ 1.86 Bond angle[8] C1-C2-C3 122.38 134.19 C2-C3-C4 123.04 134.53 Torsion angle[8] C1-C20.81 16.74 C3-C4 C1-C279.52 0.22 C5-C6 Dihedral – 8.56 angle A/ B[8] Dihedral 60.45 9.62 angle A/ C[8] Bent 52.13 4.01 angle a[8]
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0.72
24.99
0.55
0.12
1.99 0.29
7.50
2.01
0.40
17.15
3.65
0.28
6.24
0.07
0.04
[a] The geometric calculations were performed with density functional theory using Gaussian 09 program package at the B3LYP/6-311 + + G(d,p) level.
Scheme 1. Synthesis of 7 and 8.
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133.54 135.04 135.00 133.54 134.76 135.00
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Full Paper be seen, these heteroatom bridges are able to effectively force the adjacent benzene rings to become nearly planar, which is further supported by the smaller dihedral angles (A/B, 8.68 and 9.48; A/C, 9.68 and 3.78, respectively). Investigation of bond lengths in the cyclooctatetraene rings of 7 and 8 reveal that although their average bond lengths are close to the corresponding value of 9, only minor bond length alterations are observed (the deviation value is about 0.04 ), making the central eight-membered ring a conjugated arene rather than a normal cyclooctatetraene. Because the CSe bond length (1.86 ) is longer than that of the corresponding CS bond (1.72 ), the sulfur bridges cause the eight-membered core ring of 8 to be much more planar. The DFT computational results (B3LYP/6-31G + + G(d,p)) correlate well with the experimental results obtained from X-ray crystallographic studies (Table 1), with the exception of the maximum deviation of the torsional and the dihedral angle of 7 (16.7 vs. 25.08; 9.6 vs. 17.28, respectively). In the crystal structures of 7 and 8, the presence of eight methoxyl groups prohibits the intermolecular face-to face p-p stacking interaction (Figure 2 and 3). In the case of 8, both the Figure 3. Packing observed in the X-ray crystal structure of 8.
Optical properties of 7, 8, and 9 were investigated by UV/Vis and fluorescence spectroscopy. In comparison with 9, compounds 7 and 8 exhibit a sharp red-shifted lmax (by ca. 37 and 31 nm, respectively). The absorption spectra of these two heterocyclic [8]circulenes are similar; both of them show a strong absorption in the UV region (near 266 nm). Moreover, a moderate absorption band in the longer-wavelength region, ranging from 331 to 450 nm and 320 to 420 nm, respectively, was observed for 7 and 8 (Figure 4). According to theoretical calculations, this long-wavelength absorption could be attributed to p!p* excitation with the electron density shift from the sulfur or selenium atoms to the pconjugated tetraphenylene framework (HOMO, HOMO-1! LUMO, Figures S1 and S2, Supporting Information). The fluorescence spectra of 7, 8, and 9 were recorded in CH2Cl2 and are shown in Figure 4. In comparison with 9, a distinct red-shift was observed in the emission spectra of 7 and 8. Compound 7 shows blue fluorescence at 489 nm, while 8 displays fluorescence at 464 nm with two shoulders at 447 nm and 485 nm. In contrast to 9, the widths of the emission band of 7 and 8 are narrow (ca. 200 nm) and the fluorescence intensities are relatively weak, whereas the centers of emission bands are greatly red-shifted by about 108 nm and 83 nm, respectively. A comparative analysis between the dibenzo analogs [2,3,7,8-tetramethoxydibenzo[b,d]selenophene (11)[21] and [22] 2,3,7,8-tetramethoxydibenzo[b,d]thiophene (12), Figure 5] and these two heterocyclic [8]circulenes (7, 8) was also carried out. Both the longest absorption maximum (lmax, by ca. 18 and 15 nm, respectively) and the center of emission bands (by ca. 129 and 103 nm, respectively) of 7 and 8 are bathochromically shifted compared with those of 11 and 12 (Figure 4), which may suggest the existence of p-conjugation between the two corresponding dibenzo units in the heteroatom-bridged tetraphenylene framework.
Figure 2. Packing observed in the X-ray crystal structure of 7.
bend angle a and dihedral angle (A/B) values greatly decrease to 0.1 and 7.58, and the benzothiophene units and parent eight-membered ring are almost completely planar when compared with that of 7 (4.0 and 8.68, respectively). The molecular structure of 7 is slightly bent into a tub-shaped structure (7 shows a pseudo-planar structure). Adjacent molecules of 8 are found to overlap via weak C H···p interaction (2.82 and 2.88 ) between the carbon atoms of the eight-membered ring (C12 and C20) and the hydrogen atoms of the methoxy group (C20 A and C30 A) from neighboring molecules. Similarly, the crystal structure of 7 exhibits a weak CH···p interaction between molecules in a distance of 3.00 . Chem. Asian J. 2014, 9, 1 – 8
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Figure 6. Cyclic voltammogram of 7 and 8 recorded from a solution in CH3CN.
Table 2. Reduction and oxidation potentials for heteroatom-bridged tetraphenylenes referenced against the Fc/Fc + couple obtained by using square wave voltammetry.[a] Compound 7 8 13 14
Potential [V] vs. Fc/Fc +
2.51
2.21 2.13 2.47 2.34
0.77 0.86 1.12 1.19
[a] Conditions: 0.1 m in CH3CN with Bu4NBF4 as the supporting electrolyte at the scan rate of 50 mV s1. Figure 4. UV/Vis absorption (top) and fluorescence spectra (bottom) of 7, 8, 9, 11, and 12 recorded in CH2Cl2.
energy levels are in reasonable agreement with the experimental values determined by cyclic voltammetry (Table S1, Supporting Information). The aromaticity/antiaromaticity of 7 and 8 were analyzed with the nucleus-independent chemical shift (NICS) criterion at the B3LYP/6-311 + G(d,p) level of theory (Figure 7). The NICS(0) values of selenophene B (7.9 ppm) and benzene ring A (9.3 ppm) in 7, and of both rings A (8.9 ppm) and B (10.3 ppm) in 8 indicate their highly aromatic character. However, the NICS(0) values for the central eight-membered rings in 7 and 8 were calculated to be 8.2 ppm and 7.0 ppm, respectively, which could be clearly distinguished from 9 (2.3 ppm), which means that the inner eight-membered core of 7 and 8 exhibits antiaromatic character. By contrast, the NICS(0) values of A, B, and the eight-membered core rings in diselenobridged tetraphenylenes 13,[18] 15, and dithio-bridged tetraphenylenes 14[18] and 16 are smaller than those of 7 and 8. Computational studies of dications of 7, 8, 13,[18] 14,[18] 15, and 16 indicate that their inner eight-membered ring retains antiaromatic, but becomes aromatic in the dianionic state, which is a general property of other hetero[8]circulenes.[14d, e, 15d] Moreover, the rest of the benzene, thiophene, and selenophene rings of 7, 8, 13,[18] 14,[18] 15, and 16 possess aromatic character in most of the dianion and dication species.
Figure 5. Structures of 11 and 12.
The electrochemical behavior of these heterocyclic [8]circulenes (7, 8) were evaluated by using cyclic voltammetry and DFT methods. As shown in Figure 6, the cyclic voltammogram of 7 shows one irreversible oxidation wave with a peak potential at 0.77 V and a reversible reduction wave with a half-wave reduction potential at 2.21 V versus ferrocenium/ferrocene. From these potentials, the HOMO energy level (EHOMO) and LUMO energy level (ELUMO) for 7 are estimated as 5.87 eV and 2.89 eV, respectively.[23] The values of ELUMO and EHOMO of 7 are almost the same as those of 8, indicating that both compounds have similar electrochemical properties. In comparison with the previous results of diseleno-bridged tetraphenylene 13 and dithio-bridged tetraphenylene 14 (3.59 eV and 3.53 eV, respectively),[18] the HOMO and LUMO energy gaps of 7 and 8 become narrower (Table 2), suggesting that these heterocyclic [8]circulenes (7, 8) are potential candidates for p-type semiconductors.[24] Furthermore, the calculated HOMO and LUMO &
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Full Paper a 30 min period. The reaction mixture was then stirred at room temperature for 4 h and poured into ice water (50 mL). The organic layer was separated, and the aqueous layer was extracted with CH2Cl2 (20 mL 3). The combined organic layer was washed with brine, dried over MgSO4, and filtered. Next, the solvent was evaporated under reduced pressure, and the resulting residue was purified by column chromatography on silica gel (hexane/ethyl acetate 10:1) to give 10 (677.2 mg, 58 %) as a white solid. M.p.: 356.1– 358.2 8C; 1H NMR (400 MHz, CDCl3): d = 3.86 ppm (s, 24 H). 13C NMR (100 MHz, CDCl3): d = 150.8, 137.2, 119.0, 60.9 ppm; HRMS (ESI) m/z calcd for C32H24O8Br8 : 1175.4856 [M] + ; found: 1175.4861.
2,3,5,6,8,9,11,12-Octamethoxytetraphenyleno[1,16-bcd:4,5b’c’d’:8,9-b’’c’’d’’:12,13-b’’’c’’’d’’’]tetrakis(selenophene) (7) To octabromotetraphenylene 10 (583.8 mg, 0.5 mmol) in dry THF (40 mL) was added dropwise nBuLi (3.0 mL, 4.8 mmol, 1.6 m in hexane) at 78 8C, and the mixture was stirred for 3 h at the same temperature. Then Se powder (257.4 mg, 3.3 mmol) was added in one portion at 78 8C, and the mixture was stirred for 2 h at this temperature. The resulting mixture was then allowed to warm to room temperature and stirred overnight. The reaction was quenched with water (20 mL), and the aqueous solution was extracted with CH2Cl2 (25 mL 3). The combined organic phases were dried over MgSO4 and filtered, and the solvent was evaporated under reduced pressure to afford a residue, which was used directly for next step without purification. A mixture of the above residue and copper powder (800.1 mg, 12.5 mmol) was slowly heated to 250 8C and kept at this temperature for 4 h under argon. After cooling to room temperature, the reaction mixture was washed with CH2Cl2 (60 mL). The solution was concentrated and further purified by column chromatography on silica gel (hexane/ethyl acetate 5:1) to give 7 (81.3 mg, 19 % yield for two steps) as a pale yellow solid. M.p.: 324.2–325.3 8C; 1H NMR (400 MHz, CDCl3): d = 4.21 ppm (s, 24 H). 13C NMR (100 MHz, CDCl3): d = 142.5, 137.6, 132.8, 60.7 ppm; HRMS (ESI) m/z calcd for C32H24O8Se4 : 855.8132 [M] + ; found: 855.8136.
Figure 7. NICS(0) values calculated for 7–9 and 13–16.
Conclusions In summary, the first synthetic protocols for tetraseleno[8]circulene 7 and tetrathio[8]circulene 8 were developed, starting from octamethoxytetraphenylene 9. Computational results show that the central eight-membered rings in 7 and 8 impart a remarkably high antiaromatic character. The HOMO energy level of these two heterocyclic [8]circulenes suggest 7 and 8 to be potential candidates for electronic materials.
Experimental Section 2,3,5,6,8,9,11,12-Octamethoxytetraphenyleno[1,16-bcd:4,5b’c’d’:8,9-b’’c’’d’’:12,13-b’’’c’’’d’’’]tetrathiophene (8)
General Experimental Procedures All reagents and solvents were reagent grade. Further purification and drying by standard methods were employed when necessary. The plates used for thin-layer chromatography (TLC) were E. Merck silica gel 60 F254 (0.24 nm thickness) precoated on aluminum plates, and then visualized under UV light (365 nm and 254 nm) or through staining with acidic ceric ammonium molybdate and subsequent heating. Column chromatography was performed using E. Merck silica gel (230–400 mesh). NMR spectra were recorded on a Bruker Advance III 400 spectrometer (400.19 MHz for 1H and 100.62 MHz for 13C) and a Bruker 400 MHz NMR AV400Q (400.19 MHz for 1H and 100.62 MHz for 13C) at room temperature. Mass spectra (ESI, EI and FAB) were obtained with a ThermoFinnigan MAT 95 XL spectrometer and determined at an ionized voltage of 70 eV unless otherwise stated.
To a solution of octabromotetraphenylene 9 (467.1 mg, 0.4 mmol) in dry THF (40 mL) was added dropwise nBuLi (2.4 mL, 3.8 mmol, 1.6 m in hexane) at 78 8C, and the mixture was stirred for 3 h at this temperature. Then S powder (256.4 mg, 8.1 mmol) was added in one portion at - 78 8C, and the mixture was stirred for 2 h at the same temperature. The resulting mixture was allowed to warm to room temperature and stirred overnight. The reaction was quenched with water (20 mL), and the aqueous solution was extracted with CH2Cl2 (15 mL 3). The combined organic phase was dried over MgSO4 and filtered, and the solvent was evaporated under reduced pressure to give a residue which was used directly for next step without purification. A mixture of the crude product and copper powder (665.6 mg, 10.4 mmol) was slowly heated to 250 8C and kept at this temperature for 4 h under argon. After cooling to room temperature, the reaction mixture was washed with CH2Cl2 (40 mL). The solution was concentrated and further purified by column chromatography on silica gel (hexane/ethyl acetate 4:1) to give 8 (39.8 mg, 15 % yield for two steps) as a pale yellow solid. M.p.: 374.5–375.4 8C; 1H NMR (400 MHz, CDCl3): d = 4.29 ppm (s, 24 H). 13C NMR (100 MHz, CDCl3): d = 141.9, 135.1, 127.8, 61.1 ppm; HRMS (ESI) m/z calcd for C32H24O8S4 : 664.0354 [M] + ; found: 664.0359.
1,4,5,8,9,12,13,16-Octabromo-2,3,6,7,10,11,14,15-octamethoxytetraphenylene (10) Trifluoroacetic acid (30 mL), tetraphenylene 9 (544.2 mg, 1 mmol) and 98 % concentrated sulfuric acid (0.1 mL) were placed into a 50 mL round-bottomed flask. The mixture was stirred vigorously at 0 8C, and NBS (1.7 g, 9.6 mmol) was added in portions over Chem. Asian J. 2014, 9, 1 – 8
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Full Paper Crystallographic data for 8. C32H24O8S4 (664.75), Monoclinic, P21/n, 0.50 0.40 0.30 mm3, a = 9.5023(15), b = 21.924(3), c = 13.429(2) , a = 90.0, b = 95.912(3), g = 90.08, T = 173(2) K, V = 72 782.7(8) 3, Z = 4, 52 171/5048 reflections collected. The final R1 = 0.0320 (I > 2s(I)), and the final R1 = 0.0371 (for all data). The goodness of fit on F2 was 1.074.
2,3,7,8-Tetramethoxydibenzo[b,d]selenophene (11) To a solution of 2,2’-diiodo-4,4’,5,5’-tetramethoxy-1,1’-biphenyl (105.2 mg, 0.2 mmol) in dry THF (25 mL) was added dropwise nBuLi (0.3 mL, 0.48 mmol, 1.6 m in hexane) at 78 8C, and the mixture was stirred for 2 h at this temperature. Then Se powder (96.4 mg, 1.2 mmol) was added in one portion at 78 8C, and the mixture was stirred for 2 h at the same temperature. The resulting mixture was allowed to warm to room temperature and stirred overnight. The reaction was quenched with water (20 mL), and the aqueous solution was extracted with CH2Cl2 (15 mL 3). The combined organic phase was dried over MgSO4 and filtered, and the solvent was evaporated under reduced pressure to give an orange residue which was used directly for next step without purification. A mixture of the crude product and copper powder (345.6 mg, 5.4 mmol) was slowly heated to 250 8C and kept at this temperature for 2 h under argon. After cooling to room temperature, the reaction mixture was washed with CH2Cl2 (40 mL). The solution was concentrated and further purified by column chromatography on silica gel (hexane/ethyl acetate 3:1) to give 11 (60.5 mg, 86 % yield for two steps) as a white solid. M.p.: 178.4–179.3 8C; 1H NMR (400 MHz, CDCl3): d = 7.39 (s, 2 H), 7.30 (s, 2 H), 4.03 ppm (s, 6 H), 3.96 ppm (s, 6 H). 13C NMR (100 MHz, CDCl3): d = 148.6, 148.3, 131.4, 130.7, 108.1, 104.6, 56.4, 56.3 ppm; HRMS (ESI) m/z calcd for C16H16O4Se: 352.0214 [M] + ; found: 352.0221.
Acknowledgements This work was supported by an Area of Excellence Scheme established under the Research Grants Council of the Hong Kong SAR, China (Project No. AoE/P-03/08) and a grant to the State Key Laboratory of Synthetic Chemistry from the Innovation and Technology Commission. Grants from the National Natural Science Foundation of China (NSFC No. 21272199), the Chinese Academy of Sciences-Croucher Foundation Funding Scheme for Joint Laboratories, the National Natural Science Foundation of China/Research Grants Council Joint Research Scheme (NCUHK451/13), the Ministry of Education and Science of Ukraine (Project No. 0113U001694), the Shenzhen Basic Research Program (JCYJ20120619151721025) are also gratefully acknowledged. We thank Professor Thomas C.W. Mak and Dr. Chun-Kit Hau (The Chinese University of Hong Kong) for helping to carry out X-ray crystallographic analyses.
2,3,7,8-Tetramethoxydibenzo[b,d]thiophene (12) A Schlenk tube was charged with 2,2’-diiodo-4,4’,5,5’-tetramethoxy-1,1’-biphenyl (105.2 mg, 0.2 mmol), potassium sulfide (54.9 mg, 0.5 mmol), and CuI (7.7 mg, 0.04 mmol), evacuated, and backfilled with argon. Next, CH3CN (3.0 mL) was injected. The reaction mixture was stirred at 140 8C and was monitored by TLC until the starting material disappeared. The cooled reaction mixture was partitioned between CH2Cl2 (30 mL) and water (20 mL), and the aqueous solution was extracted with CH2Cl2 (15 mL 3). The organic layer was washed with water (20 mL) and brine (20 mL), dried over Na2SO4, and concentrated under reduced pressure. The resulting residue was purified by column chromatography on silica gel (hexane/ethyl acetate 3:1) to give 12 (48.6 mg, 80 %) as a white solid. M.p.: 189.1–189.8 8C; 1H NMR (400 MHz, CDCl3): d = 7.42 (s, 2 H), 7.26 (s, 2 H), 4.03 (s, 6 H), 3.97 ppm (s, 6 H). 13C NMR (100 MHz, CDCl3): d = 148.7, 148.06, 131.5, 128.8, 104.9, 103.0, 56.4, 56.3 ppm; HRMS (ESI) m/z calcd for C16H16O4S: 304.0769 [M] + ; found: 304.0773.
Keywords: [8]circulene · antiaromaticity · density functional theory calculation · electrochemistry · photophysics [1] a) J. H. Dopper, H. Wynberg, Tetrahedron Lett. 1972, 13, 763 – 766; b) J. H. Dopper, D. Oudman, H. Wynberg, J. Am. Chem. Soc. 1973, 95, 3692 – 3698; c) J. H. Dopper, H. Wynberg, J. Org. Chem. 1975, 40, 1957 – 1966. [2] a) R. Bharat, T. Bhola, A. Bally, M. K. Valente, L. Cyran´ski, S. Dobrzycki, M. Spain, P. Rempała, M. R. Chin, B. T. King, Angew. Chem. Int. Ed. 2010, 49, 399 – 402; Angew. Chem. 2010, 122, 409 – 412; b) B. Kumar, B. T. King, J. Org. Chem. 2012, 77, 10617 – 10622. [3] a) W. E. Barth, R. G. Lawton, J. Am. Chem. Soc. 1966, 88, 380 – 381; b) W. E. Barth, R. G. Lawton, J. Am. Chem. Soc. 1971, 93, 1730 – 1745; c) A. Sygula, Eur. J. Org. Chem. 2011, 1611 – 1625; d) Y.-T. Wu, J. S. Siegel, Chem. Rev. 2006, 106, 4843 – 4867. [4] a) R. Scholl, K. Meyer, Ber. Dtsch. Chem. Ges. A 1932, 65, 902; b) E. Clar, Polycyclic Hydrocarbons, Academic Press, New York, NY, 1964. [5] a) K. Yamamoto, T. Harada, M. Nakazaki, T. Naka, Y. Kai, S. Harada, N. Kasai, J. Am. Chem. Soc. 1983, 105, 7171 – 7172; b) K. Yamamoto, H. Sonobe, H. Matsubara, M. Sato, S. Okamoto, K. Kitaura, Angew. Chem. Int. Ed. Engl. 1996, 35, 69 – 70; Angew. Chem. 1996, 108, 69 – 70; c) K. Yamamoto, T. Harada, Y. Okamoto, H. Chikamatsu, M. Nakazaki, Y. Kai, T. Nakao, M. Tanaka, S. Harada, N. Kasai, J. Am. Chem. Soc. 1988, 110, 3578 – 3584; d) M. Shen, I. S. Ignatyev, Y. Xie, H. F. Schaefer, J. Phys. Chem. 1993, 97, 3212 – 3216. [6] a) C. N. Feng, M. Kuo, Y. Wu, Angew. Chem. Int. Ed. 2013, 52, 7791 – 7794; Angew. Chem. 2013, 125, 7945 – 7948; b) Y. Sakamoto, T. Suzuki, J. Am. Chem. Soc. 2013, 135, 14074 – 14077; c) R. W. Miller, A. K. Duancan, S. T. Schneebeli, D. L. Gray, A. C. Whalley, Chem. Eur. J. 2014, 20, 3705 – 3711. [7] a) T. Liljefors, O. Wennerstrom, Tetrahedron 1977, 33, 2999 – 3003; b) R. Salcedo, L. E. Sansoresa, A. Picazoa, L. Sanson, THEOCHEM 2004, 678, 211 – 215. [8] a) H. G. H. Erdtman, Proc. R. Soc. London Ser. A 1933, 143, 191 – 222; b) H. Erdtman, H. E. Hçberg, Chem. Commun. 1968, 773 – 774; c) H. Erdtman, H. E. Hçberg, Tetrahedron Lett. 1970, 11, 3389 – 3392. [9] a) H. E. Hçberg, Acta Chem. Scand. 1973, 27, 2579 – 2596; b) P. D. J. Grootenhuis, D. C. Roe, P. A. Kollman, I. D. Kuntz, J. Comput.-Aided Mol. Des. 1994, 8, 731 – 775; c) J. Eskildsen, T. Reenberg, J. B. Christensen, Eur.
X-ray crystallography Single-crystal X-ray diffraction was conducted on Agilent SuperNova diffractometer. The crystal structure was solved by direct methods SIR2004 and refined by full matrix least-squares on F2 by means of SHELXL 97. The calculated positions of the hydrogen atoms were included in the final refinement. CCDC 1022491 (7), CCDC 1022490 (8), and CCDC 1022489 (9) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Crystallographic data for 7. C32H24O8Se4 (852.35), Monoclinic, C2/c, a = 11.3080(7), b = 23.2084(15), c= 0.50 0.50 0.50 mm3, 11.0168(7) , a = 90.0(2), b = 94.2(10), g = 90.0(2)8, T = 173 (2) K, V = 2883.4(3) 3, Z = 4, 14651/2615 reflections collected. The final R1 = 0.0190 (I > 2s(I)), and the final R1 = 0.0233 (for all data). The goodness of fit on F2 was 1.046.
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Received: September 2, 2014 Published online on && &&, 0000
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FULL PAPER & Polycycles
Quite a character: Novel sulfur and selenium-bridged [8]circulenes were prepared from octabromotetraphenylene. Computational results show that the central eight-membered rings in these [8]circulenes have a remarkably high antiaromatic character.
X. Xiong, C.-L. Deng, B. F. Minaev, G. V. Baryshnikov, X.-S. Peng, H. N. C. Wong* && – && Tetrathio and Tetraseleno[8]circulenes: Synthesis, Structures, and Properties
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Tetrathio and Tetraseleno[8]circulenes: Synthesis, Structures, and Properties Xiaodong Xiong,[a] Chun-Lin Deng,[a] Boris F. Minaev,[c] Gleb V. Baryshnikov,[c] Xiao-Shui Peng,[a, b] and Henry N. C. Wong*[a, b]
applications as electronic materials. The antiaromatic nature of tetrathio[8]circulene and tetraselenium[8]circulene was studied by computational methods, and the NICS computational results reveal that the central eight-membered ring has highly antiaromatic character.
Abstract: Novel sulfur and selenium-bridged [8]circulenes were prepared from octabromotetraphenylene. Structures of these compounds were unambiguously confirmed by X-ray crystallographic analyses. Photophysical and electrochemical investigations of these [8]circulenes suggest their potential
Introduction In the family of polycyclic aromatic compounds, [n]circulenes are macrocyclic arenes produced by benzene rings being completely surrounded and fused around central n-sided polygons.[1] Only four members of this homologous series of compounds have been successfully prepared up to 2013: [4]circulene (quadrannulene),[2] [5]circulene (corannulene),[3] [6]circulene (coronene),[4] and [7]circulene (pleiadannulene).[5] The conspicuous geometric features of these circulenes change from a bow (quadrannulene and corannulene) through a plane (coronene) to a saddle (pleiadannulene). Recently, the synthesis of the parent [8]circulene 1 (in Figure 1 without side substituents for clarity) has been reported by Wu and coworkers.[6a] [8]Circulene 1 had been predicted previously to be aromatic but with nonplanar tub-shaped geometry belonging to D2d symmetry, and with alternating single and double bonds.[7] Computational studies are consistent with the newly prepared [8]circulene derivative 2, in which the saddle structure was unambiguously confirmed by an X-ray crystallographic study.[6b, c] By contrast,
Figure 1. Representative examples of [8]circulenes.
the corresponding tetraoxa[8]circulene 3 has been known for a long time, and was firstly prepared in 1968 by treatment of 1,4-benzoquinone with a strong acid. X-ray diffraction results suggest that its central eight-membered ring is constrained to adopt a planar structure.[8] Recently, a number of tetraoxa[8]circulene derivatives[9] and their planar analogs, such as tetracyclopenta[def,jkl,pqr,vwx]-tetraphenylene (TCT) 4,[10] octathio[8]circulene 5,[11] nitrogen atom containing diazadioxa[8]circulene 6,[12] and tetrathiotetraseleno[8]circulene[13] have been successfully prepared. Analyses of their experimental and computational data show that these planarized cyclooctatetraenes are antiaromatic.[12, 14] As antiaromatic compounds often display unique electrochemical and optical properties on the entire pconjugated systems, studies of the geometry and aromatic/antiaromatic properties of heterocyclic [8]circulene have inevitably attracted an increasing attention from many chemists.[15] Moreover, these [8]circulenes are potential candidates as DNA intercalators,[9b] liquid crystalline materials,[9c, h] stable cation-
[a] Dr. X. Xiong, C.-L. Deng, Dr. X.-S. Peng, Prof. Dr. H. N. C. Wong Department of Chemistry, State Key Laboratory of Synthetic Chemistry Center of Novel Functional Molecules, and Institute of Molecular Functional Materials The Chinese University of Hong Kong Shatin, New Territories, Hong Kong SAR (China) Fax: (+ 852) 26035315 E-mail: [email protected] [b] Dr. X.-S. Peng, Prof. Dr. H. N. C. Wong Shenzhen Center of Novel Functional Molecules Shenzhen Research Institute The Chinese University of Hong Kong No.10, Second Yuexing Road, Shenzhen 518507 (China) [c] Prof. Dr. B. F. Minaev, Dr. G. V. Baryshnikov Bohdan Khmelnytsky National University 18301, Cherkasy (Ukraine) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201403028. Chem. Asian J. 2014, 9, 1 – 8
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Full Paper radical salts,[7d] organic light-emitting diodes,[9f] and organic semiconductors.[13, 14b, 15h, i] Therefore, syntheses of [8]circulenes are always synthetically important. Experimentally, incorporation of triple bonds into eightmembered rings, annulation of small-membered rings, and fusion of rigid planar p-systems to tetraphenylenes could all make their central cyclooctatetraene rings planar.[8–12, 16] As a result of the planarity, considerable antiaromatic paratropicity could be detected.[14b, 15a, 17] In this field, Hçgberg,[8, 9a] Nishinaga,[14b] and Pittelkow[9e–g, 12] synthesized a class of planar antiaromatic cyclooctatetraenes by introducing heteroatom bridges. Very recently, we also reported the synthesis and studies of dioxo-, diaza-, dithio-, and diseleno-bridged partially planar tetraphenylenes.[18] Inspired by these encouraging results, we envisioned that the synthesis of tetraseleno[8]circulene 7 and tetrathio[8]circulene 8 could be achieved by insertion of selenium and sulfur bridges in the bay regions of tetraphenylene. Herein, we describe the first synthesis of [8]circulenes 7 and 8, as well as studies of their electrochemical, photophysical, and antiaromatic properties.
with NBS in trifluoroacetic acid to afford octabromide 10 in 58 % yield. Then 10 was treated with an excess of nBuLi, resulting in its complete lithiation. Addition of selenium powder in one portion to the resulting lithium salt led to the formation of the polyselenium tetraphenylene intermediate, which, when subjected to thermal deselenation with copper powder at 250 8C, afforded the desired [8]circulene 7 in 19 % yield (Scheme 1). In a similar strategy, [8]circulene 8 was obtained in an overall 15 % yield, starting also from octabromotetraphenylene 10. Structures of 7 and 8 were confirmed by X-ray crystallographic studies. In this manner, we have developed an effective method to construct these intriguing molecular architectures. As shown in Table 1, while X-ray crystallographic analyses indicate that tetraphenylene 9[19] and [8]circulene 7 are saddleshaped, [8]circulene 8 can be shown to possess a cyclic 8p electron central eight-membered ring in an essentially planar conformation. As regarding the inner angles of the central eight-membered ring, the average values in the crystal structures of 7 and 8 are found to be 134.2 and 134.98, respectively, which are larger than the inner angle of a regular tetraphenylene [viz. 9 (122.78)]. However, the average bent angles (a) of 7 and 8 are 4.08 and 0.18, respectively, which are substantially less than that of 9 (52.18). Consequently, the eight-membered ring of 7 is less puckered than that of tetraphenylene 9. As can
Results and Discussion In view of the possibility that it is difficult to directly lithiate octamethoxytetraphenylene 9[19] according to a known procedure,[20] we therefore utilized an indirect method by introducing eight bromine atoms to 9. Thus, 9 underwent bromination
Table 1. Selected structural data analysis of heterocyclic [8]circulenes.[a]! 9 X-ray
7 X-ray
8 Calcd. X-ray
Calcd.
Bond 1.39/ length[] 1.49/
1.49/ 1.45/
1.49/ 1.45/
1.47/ 1.43/
1.48/ 1.44/
1.42/ 1.88
1.42/ 1.72
1.42/ 1.74
r1/r2/r3/r4 1.40/– 1.42/ 1.86 Bond angle[8] C1-C2-C3 122.38 134.19 C2-C3-C4 123.04 134.53 Torsion angle[8] C1-C20.81 16.74 C3-C4 C1-C279.52 0.22 C5-C6 Dihedral – 8.56 angle A/ B[8] Dihedral 60.45 9.62 angle A/ C[8] Bent 52.13 4.01 angle a[8]
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24.99
0.55
0.12
1.99 0.29
7.50
2.01
0.40
17.15
3.65
0.28
6.24
0.07
0.04
[a] The geometric calculations were performed with density functional theory using Gaussian 09 program package at the B3LYP/6-311 + + G(d,p) level.
Scheme 1. Synthesis of 7 and 8.
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133.54 135.04 135.00 133.54 134.76 135.00
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Full Paper be seen, these heteroatom bridges are able to effectively force the adjacent benzene rings to become nearly planar, which is further supported by the smaller dihedral angles (A/B, 8.68 and 9.48; A/C, 9.68 and 3.78, respectively). Investigation of bond lengths in the cyclooctatetraene rings of 7 and 8 reveal that although their average bond lengths are close to the corresponding value of 9, only minor bond length alterations are observed (the deviation value is about 0.04 ), making the central eight-membered ring a conjugated arene rather than a normal cyclooctatetraene. Because the CSe bond length (1.86 ) is longer than that of the corresponding CS bond (1.72 ), the sulfur bridges cause the eight-membered core ring of 8 to be much more planar. The DFT computational results (B3LYP/6-31G + + G(d,p)) correlate well with the experimental results obtained from X-ray crystallographic studies (Table 1), with the exception of the maximum deviation of the torsional and the dihedral angle of 7 (16.7 vs. 25.08; 9.6 vs. 17.28, respectively). In the crystal structures of 7 and 8, the presence of eight methoxyl groups prohibits the intermolecular face-to face p-p stacking interaction (Figure 2 and 3). In the case of 8, both the Figure 3. Packing observed in the X-ray crystal structure of 8.
Optical properties of 7, 8, and 9 were investigated by UV/Vis and fluorescence spectroscopy. In comparison with 9, compounds 7 and 8 exhibit a sharp red-shifted lmax (by ca. 37 and 31 nm, respectively). The absorption spectra of these two heterocyclic [8]circulenes are similar; both of them show a strong absorption in the UV region (near 266 nm). Moreover, a moderate absorption band in the longer-wavelength region, ranging from 331 to 450 nm and 320 to 420 nm, respectively, was observed for 7 and 8 (Figure 4). According to theoretical calculations, this long-wavelength absorption could be attributed to p!p* excitation with the electron density shift from the sulfur or selenium atoms to the pconjugated tetraphenylene framework (HOMO, HOMO-1! LUMO, Figures S1 and S2, Supporting Information). The fluorescence spectra of 7, 8, and 9 were recorded in CH2Cl2 and are shown in Figure 4. In comparison with 9, a distinct red-shift was observed in the emission spectra of 7 and 8. Compound 7 shows blue fluorescence at 489 nm, while 8 displays fluorescence at 464 nm with two shoulders at 447 nm and 485 nm. In contrast to 9, the widths of the emission band of 7 and 8 are narrow (ca. 200 nm) and the fluorescence intensities are relatively weak, whereas the centers of emission bands are greatly red-shifted by about 108 nm and 83 nm, respectively. A comparative analysis between the dibenzo analogs [2,3,7,8-tetramethoxydibenzo[b,d]selenophene (11)[21] and [22] 2,3,7,8-tetramethoxydibenzo[b,d]thiophene (12), Figure 5] and these two heterocyclic [8]circulenes (7, 8) was also carried out. Both the longest absorption maximum (lmax, by ca. 18 and 15 nm, respectively) and the center of emission bands (by ca. 129 and 103 nm, respectively) of 7 and 8 are bathochromically shifted compared with those of 11 and 12 (Figure 4), which may suggest the existence of p-conjugation between the two corresponding dibenzo units in the heteroatom-bridged tetraphenylene framework.
Figure 2. Packing observed in the X-ray crystal structure of 7.
bend angle a and dihedral angle (A/B) values greatly decrease to 0.1 and 7.58, and the benzothiophene units and parent eight-membered ring are almost completely planar when compared with that of 7 (4.0 and 8.68, respectively). The molecular structure of 7 is slightly bent into a tub-shaped structure (7 shows a pseudo-planar structure). Adjacent molecules of 8 are found to overlap via weak C H···p interaction (2.82 and 2.88 ) between the carbon atoms of the eight-membered ring (C12 and C20) and the hydrogen atoms of the methoxy group (C20 A and C30 A) from neighboring molecules. Similarly, the crystal structure of 7 exhibits a weak CH···p interaction between molecules in a distance of 3.00 . Chem. Asian J. 2014, 9, 1 – 8
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Figure 6. Cyclic voltammogram of 7 and 8 recorded from a solution in CH3CN.
Table 2. Reduction and oxidation potentials for heteroatom-bridged tetraphenylenes referenced against the Fc/Fc + couple obtained by using square wave voltammetry.[a] Compound 7 8 13 14
Potential [V] vs. Fc/Fc +
2.51
2.21 2.13 2.47 2.34
0.77 0.86 1.12 1.19
[a] Conditions: 0.1 m in CH3CN with Bu4NBF4 as the supporting electrolyte at the scan rate of 50 mV s1. Figure 4. UV/Vis absorption (top) and fluorescence spectra (bottom) of 7, 8, 9, 11, and 12 recorded in CH2Cl2.
energy levels are in reasonable agreement with the experimental values determined by cyclic voltammetry (Table S1, Supporting Information). The aromaticity/antiaromaticity of 7 and 8 were analyzed with the nucleus-independent chemical shift (NICS) criterion at the B3LYP/6-311 + G(d,p) level of theory (Figure 7). The NICS(0) values of selenophene B (7.9 ppm) and benzene ring A (9.3 ppm) in 7, and of both rings A (8.9 ppm) and B (10.3 ppm) in 8 indicate their highly aromatic character. However, the NICS(0) values for the central eight-membered rings in 7 and 8 were calculated to be 8.2 ppm and 7.0 ppm, respectively, which could be clearly distinguished from 9 (2.3 ppm), which means that the inner eight-membered core of 7 and 8 exhibits antiaromatic character. By contrast, the NICS(0) values of A, B, and the eight-membered core rings in diselenobridged tetraphenylenes 13,[18] 15, and dithio-bridged tetraphenylenes 14[18] and 16 are smaller than those of 7 and 8. Computational studies of dications of 7, 8, 13,[18] 14,[18] 15, and 16 indicate that their inner eight-membered ring retains antiaromatic, but becomes aromatic in the dianionic state, which is a general property of other hetero[8]circulenes.[14d, e, 15d] Moreover, the rest of the benzene, thiophene, and selenophene rings of 7, 8, 13,[18] 14,[18] 15, and 16 possess aromatic character in most of the dianion and dication species.
Figure 5. Structures of 11 and 12.
The electrochemical behavior of these heterocyclic [8]circulenes (7, 8) were evaluated by using cyclic voltammetry and DFT methods. As shown in Figure 6, the cyclic voltammogram of 7 shows one irreversible oxidation wave with a peak potential at 0.77 V and a reversible reduction wave with a half-wave reduction potential at 2.21 V versus ferrocenium/ferrocene. From these potentials, the HOMO energy level (EHOMO) and LUMO energy level (ELUMO) for 7 are estimated as 5.87 eV and 2.89 eV, respectively.[23] The values of ELUMO and EHOMO of 7 are almost the same as those of 8, indicating that both compounds have similar electrochemical properties. In comparison with the previous results of diseleno-bridged tetraphenylene 13 and dithio-bridged tetraphenylene 14 (3.59 eV and 3.53 eV, respectively),[18] the HOMO and LUMO energy gaps of 7 and 8 become narrower (Table 2), suggesting that these heterocyclic [8]circulenes (7, 8) are potential candidates for p-type semiconductors.[24] Furthermore, the calculated HOMO and LUMO &
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Full Paper a 30 min period. The reaction mixture was then stirred at room temperature for 4 h and poured into ice water (50 mL). The organic layer was separated, and the aqueous layer was extracted with CH2Cl2 (20 mL 3). The combined organic layer was washed with brine, dried over MgSO4, and filtered. Next, the solvent was evaporated under reduced pressure, and the resulting residue was purified by column chromatography on silica gel (hexane/ethyl acetate 10:1) to give 10 (677.2 mg, 58 %) as a white solid. M.p.: 356.1– 358.2 8C; 1H NMR (400 MHz, CDCl3): d = 3.86 ppm (s, 24 H). 13C NMR (100 MHz, CDCl3): d = 150.8, 137.2, 119.0, 60.9 ppm; HRMS (ESI) m/z calcd for C32H24O8Br8 : 1175.4856 [M] + ; found: 1175.4861.
2,3,5,6,8,9,11,12-Octamethoxytetraphenyleno[1,16-bcd:4,5b’c’d’:8,9-b’’c’’d’’:12,13-b’’’c’’’d’’’]tetrakis(selenophene) (7) To octabromotetraphenylene 10 (583.8 mg, 0.5 mmol) in dry THF (40 mL) was added dropwise nBuLi (3.0 mL, 4.8 mmol, 1.6 m in hexane) at 78 8C, and the mixture was stirred for 3 h at the same temperature. Then Se powder (257.4 mg, 3.3 mmol) was added in one portion at 78 8C, and the mixture was stirred for 2 h at this temperature. The resulting mixture was then allowed to warm to room temperature and stirred overnight. The reaction was quenched with water (20 mL), and the aqueous solution was extracted with CH2Cl2 (25 mL 3). The combined organic phases were dried over MgSO4 and filtered, and the solvent was evaporated under reduced pressure to afford a residue, which was used directly for next step without purification. A mixture of the above residue and copper powder (800.1 mg, 12.5 mmol) was slowly heated to 250 8C and kept at this temperature for 4 h under argon. After cooling to room temperature, the reaction mixture was washed with CH2Cl2 (60 mL). The solution was concentrated and further purified by column chromatography on silica gel (hexane/ethyl acetate 5:1) to give 7 (81.3 mg, 19 % yield for two steps) as a pale yellow solid. M.p.: 324.2–325.3 8C; 1H NMR (400 MHz, CDCl3): d = 4.21 ppm (s, 24 H). 13C NMR (100 MHz, CDCl3): d = 142.5, 137.6, 132.8, 60.7 ppm; HRMS (ESI) m/z calcd for C32H24O8Se4 : 855.8132 [M] + ; found: 855.8136.
Figure 7. NICS(0) values calculated for 7–9 and 13–16.
Conclusions In summary, the first synthetic protocols for tetraseleno[8]circulene 7 and tetrathio[8]circulene 8 were developed, starting from octamethoxytetraphenylene 9. Computational results show that the central eight-membered rings in 7 and 8 impart a remarkably high antiaromatic character. The HOMO energy level of these two heterocyclic [8]circulenes suggest 7 and 8 to be potential candidates for electronic materials.
Experimental Section 2,3,5,6,8,9,11,12-Octamethoxytetraphenyleno[1,16-bcd:4,5b’c’d’:8,9-b’’c’’d’’:12,13-b’’’c’’’d’’’]tetrathiophene (8)
General Experimental Procedures All reagents and solvents were reagent grade. Further purification and drying by standard methods were employed when necessary. The plates used for thin-layer chromatography (TLC) were E. Merck silica gel 60 F254 (0.24 nm thickness) precoated on aluminum plates, and then visualized under UV light (365 nm and 254 nm) or through staining with acidic ceric ammonium molybdate and subsequent heating. Column chromatography was performed using E. Merck silica gel (230–400 mesh). NMR spectra were recorded on a Bruker Advance III 400 spectrometer (400.19 MHz for 1H and 100.62 MHz for 13C) and a Bruker 400 MHz NMR AV400Q (400.19 MHz for 1H and 100.62 MHz for 13C) at room temperature. Mass spectra (ESI, EI and FAB) were obtained with a ThermoFinnigan MAT 95 XL spectrometer and determined at an ionized voltage of 70 eV unless otherwise stated.
To a solution of octabromotetraphenylene 9 (467.1 mg, 0.4 mmol) in dry THF (40 mL) was added dropwise nBuLi (2.4 mL, 3.8 mmol, 1.6 m in hexane) at 78 8C, and the mixture was stirred for 3 h at this temperature. Then S powder (256.4 mg, 8.1 mmol) was added in one portion at - 78 8C, and the mixture was stirred for 2 h at the same temperature. The resulting mixture was allowed to warm to room temperature and stirred overnight. The reaction was quenched with water (20 mL), and the aqueous solution was extracted with CH2Cl2 (15 mL 3). The combined organic phase was dried over MgSO4 and filtered, and the solvent was evaporated under reduced pressure to give a residue which was used directly for next step without purification. A mixture of the crude product and copper powder (665.6 mg, 10.4 mmol) was slowly heated to 250 8C and kept at this temperature for 4 h under argon. After cooling to room temperature, the reaction mixture was washed with CH2Cl2 (40 mL). The solution was concentrated and further purified by column chromatography on silica gel (hexane/ethyl acetate 4:1) to give 8 (39.8 mg, 15 % yield for two steps) as a pale yellow solid. M.p.: 374.5–375.4 8C; 1H NMR (400 MHz, CDCl3): d = 4.29 ppm (s, 24 H). 13C NMR (100 MHz, CDCl3): d = 141.9, 135.1, 127.8, 61.1 ppm; HRMS (ESI) m/z calcd for C32H24O8S4 : 664.0354 [M] + ; found: 664.0359.
1,4,5,8,9,12,13,16-Octabromo-2,3,6,7,10,11,14,15-octamethoxytetraphenylene (10) Trifluoroacetic acid (30 mL), tetraphenylene 9 (544.2 mg, 1 mmol) and 98 % concentrated sulfuric acid (0.1 mL) were placed into a 50 mL round-bottomed flask. The mixture was stirred vigorously at 0 8C, and NBS (1.7 g, 9.6 mmol) was added in portions over Chem. Asian J. 2014, 9, 1 – 8
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Full Paper Crystallographic data for 8. C32H24O8S4 (664.75), Monoclinic, P21/n, 0.50 0.40 0.30 mm3, a = 9.5023(15), b = 21.924(3), c = 13.429(2) , a = 90.0, b = 95.912(3), g = 90.08, T = 173(2) K, V = 72 782.7(8) 3, Z = 4, 52 171/5048 reflections collected. The final R1 = 0.0320 (I > 2s(I)), and the final R1 = 0.0371 (for all data). The goodness of fit on F2 was 1.074.
2,3,7,8-Tetramethoxydibenzo[b,d]selenophene (11) To a solution of 2,2’-diiodo-4,4’,5,5’-tetramethoxy-1,1’-biphenyl (105.2 mg, 0.2 mmol) in dry THF (25 mL) was added dropwise nBuLi (0.3 mL, 0.48 mmol, 1.6 m in hexane) at 78 8C, and the mixture was stirred for 2 h at this temperature. Then Se powder (96.4 mg, 1.2 mmol) was added in one portion at 78 8C, and the mixture was stirred for 2 h at the same temperature. The resulting mixture was allowed to warm to room temperature and stirred overnight. The reaction was quenched with water (20 mL), and the aqueous solution was extracted with CH2Cl2 (15 mL 3). The combined organic phase was dried over MgSO4 and filtered, and the solvent was evaporated under reduced pressure to give an orange residue which was used directly for next step without purification. A mixture of the crude product and copper powder (345.6 mg, 5.4 mmol) was slowly heated to 250 8C and kept at this temperature for 2 h under argon. After cooling to room temperature, the reaction mixture was washed with CH2Cl2 (40 mL). The solution was concentrated and further purified by column chromatography on silica gel (hexane/ethyl acetate 3:1) to give 11 (60.5 mg, 86 % yield for two steps) as a white solid. M.p.: 178.4–179.3 8C; 1H NMR (400 MHz, CDCl3): d = 7.39 (s, 2 H), 7.30 (s, 2 H), 4.03 ppm (s, 6 H), 3.96 ppm (s, 6 H). 13C NMR (100 MHz, CDCl3): d = 148.6, 148.3, 131.4, 130.7, 108.1, 104.6, 56.4, 56.3 ppm; HRMS (ESI) m/z calcd for C16H16O4Se: 352.0214 [M] + ; found: 352.0221.
Acknowledgements This work was supported by an Area of Excellence Scheme established under the Research Grants Council of the Hong Kong SAR, China (Project No. AoE/P-03/08) and a grant to the State Key Laboratory of Synthetic Chemistry from the Innovation and Technology Commission. Grants from the National Natural Science Foundation of China (NSFC No. 21272199), the Chinese Academy of Sciences-Croucher Foundation Funding Scheme for Joint Laboratories, the National Natural Science Foundation of China/Research Grants Council Joint Research Scheme (NCUHK451/13), the Ministry of Education and Science of Ukraine (Project No. 0113U001694), the Shenzhen Basic Research Program (JCYJ20120619151721025) are also gratefully acknowledged. We thank Professor Thomas C.W. Mak and Dr. Chun-Kit Hau (The Chinese University of Hong Kong) for helping to carry out X-ray crystallographic analyses.
2,3,7,8-Tetramethoxydibenzo[b,d]thiophene (12) A Schlenk tube was charged with 2,2’-diiodo-4,4’,5,5’-tetramethoxy-1,1’-biphenyl (105.2 mg, 0.2 mmol), potassium sulfide (54.9 mg, 0.5 mmol), and CuI (7.7 mg, 0.04 mmol), evacuated, and backfilled with argon. Next, CH3CN (3.0 mL) was injected. The reaction mixture was stirred at 140 8C and was monitored by TLC until the starting material disappeared. The cooled reaction mixture was partitioned between CH2Cl2 (30 mL) and water (20 mL), and the aqueous solution was extracted with CH2Cl2 (15 mL 3). The organic layer was washed with water (20 mL) and brine (20 mL), dried over Na2SO4, and concentrated under reduced pressure. The resulting residue was purified by column chromatography on silica gel (hexane/ethyl acetate 3:1) to give 12 (48.6 mg, 80 %) as a white solid. M.p.: 189.1–189.8 8C; 1H NMR (400 MHz, CDCl3): d = 7.42 (s, 2 H), 7.26 (s, 2 H), 4.03 (s, 6 H), 3.97 ppm (s, 6 H). 13C NMR (100 MHz, CDCl3): d = 148.7, 148.06, 131.5, 128.8, 104.9, 103.0, 56.4, 56.3 ppm; HRMS (ESI) m/z calcd for C16H16O4S: 304.0769 [M] + ; found: 304.0773.
Keywords: [8]circulene · antiaromaticity · density functional theory calculation · electrochemistry · photophysics [1] a) J. H. Dopper, H. Wynberg, Tetrahedron Lett. 1972, 13, 763 – 766; b) J. H. Dopper, D. Oudman, H. Wynberg, J. Am. Chem. Soc. 1973, 95, 3692 – 3698; c) J. H. Dopper, H. Wynberg, J. Org. Chem. 1975, 40, 1957 – 1966. [2] a) R. Bharat, T. Bhola, A. Bally, M. K. Valente, L. Cyran´ski, S. Dobrzycki, M. Spain, P. Rempała, M. R. Chin, B. T. King, Angew. Chem. Int. Ed. 2010, 49, 399 – 402; Angew. Chem. 2010, 122, 409 – 412; b) B. Kumar, B. T. King, J. Org. Chem. 2012, 77, 10617 – 10622. [3] a) W. E. Barth, R. G. Lawton, J. Am. Chem. Soc. 1966, 88, 380 – 381; b) W. E. Barth, R. G. Lawton, J. Am. Chem. Soc. 1971, 93, 1730 – 1745; c) A. Sygula, Eur. J. Org. Chem. 2011, 1611 – 1625; d) Y.-T. Wu, J. S. Siegel, Chem. Rev. 2006, 106, 4843 – 4867. [4] a) R. Scholl, K. Meyer, Ber. Dtsch. Chem. Ges. A 1932, 65, 902; b) E. Clar, Polycyclic Hydrocarbons, Academic Press, New York, NY, 1964. [5] a) K. Yamamoto, T. Harada, M. Nakazaki, T. Naka, Y. Kai, S. Harada, N. Kasai, J. Am. Chem. Soc. 1983, 105, 7171 – 7172; b) K. Yamamoto, H. Sonobe, H. Matsubara, M. Sato, S. Okamoto, K. Kitaura, Angew. Chem. Int. Ed. Engl. 1996, 35, 69 – 70; Angew. Chem. 1996, 108, 69 – 70; c) K. Yamamoto, T. Harada, Y. Okamoto, H. Chikamatsu, M. Nakazaki, Y. Kai, T. Nakao, M. Tanaka, S. Harada, N. Kasai, J. Am. Chem. Soc. 1988, 110, 3578 – 3584; d) M. Shen, I. S. Ignatyev, Y. Xie, H. F. Schaefer, J. Phys. Chem. 1993, 97, 3212 – 3216. [6] a) C. N. Feng, M. Kuo, Y. Wu, Angew. Chem. Int. Ed. 2013, 52, 7791 – 7794; Angew. Chem. 2013, 125, 7945 – 7948; b) Y. Sakamoto, T. Suzuki, J. Am. Chem. Soc. 2013, 135, 14074 – 14077; c) R. W. Miller, A. K. Duancan, S. T. Schneebeli, D. L. Gray, A. C. Whalley, Chem. Eur. J. 2014, 20, 3705 – 3711. [7] a) T. Liljefors, O. Wennerstrom, Tetrahedron 1977, 33, 2999 – 3003; b) R. Salcedo, L. E. Sansoresa, A. Picazoa, L. Sanson, THEOCHEM 2004, 678, 211 – 215. [8] a) H. G. H. Erdtman, Proc. R. Soc. London Ser. A 1933, 143, 191 – 222; b) H. Erdtman, H. E. Hçberg, Chem. Commun. 1968, 773 – 774; c) H. Erdtman, H. E. Hçberg, Tetrahedron Lett. 1970, 11, 3389 – 3392. [9] a) H. E. Hçberg, Acta Chem. Scand. 1973, 27, 2579 – 2596; b) P. D. J. Grootenhuis, D. C. Roe, P. A. Kollman, I. D. Kuntz, J. Comput.-Aided Mol. Des. 1994, 8, 731 – 775; c) J. Eskildsen, T. Reenberg, J. B. Christensen, Eur.
X-ray crystallography Single-crystal X-ray diffraction was conducted on Agilent SuperNova diffractometer. The crystal structure was solved by direct methods SIR2004 and refined by full matrix least-squares on F2 by means of SHELXL 97. The calculated positions of the hydrogen atoms were included in the final refinement. CCDC 1022491 (7), CCDC 1022490 (8), and CCDC 1022489 (9) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Crystallographic data for 7. C32H24O8Se4 (852.35), Monoclinic, C2/c, a = 11.3080(7), b = 23.2084(15), c= 0.50 0.50 0.50 mm3, 11.0168(7) , a = 90.0(2), b = 94.2(10), g = 90.0(2)8, T = 173 (2) K, V = 2883.4(3) 3, Z = 4, 14651/2615 reflections collected. The final R1 = 0.0190 (I > 2s(I)), and the final R1 = 0.0233 (for all data). The goodness of fit on F2 was 1.046.
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FULL PAPER & Polycycles
Quite a character: Novel sulfur and selenium-bridged [8]circulenes were prepared from octabromotetraphenylene. Computational results show that the central eight-membered rings in these [8]circulenes have a remarkably high antiaromatic character.
X. Xiong, C.-L. Deng, B. F. Minaev, G. V. Baryshnikov, X.-S. Peng, H. N. C. Wong* && – && Tetrathio and Tetraseleno[8]circulenes: Synthesis, Structures, and Properties
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