Letter pubs.acs.org/OrgLett
Synthesis of Dibenzo[h,rst]pentaphenes and Dibenzo[fg,qr]pentacenes by the Chemoselective C−O Arylation of Dimethoxyanthraquinones Yusuke Suzuki,† Kohei Yamada,† Kentaro Watanabe,† Takuya Kochi,† Yutaka Ie,‡,§ Yoshio Aso,‡ and Fumitoshi Kakiuchi*,†,§ †
Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan ‡ The Institute of Science and Industrial Research (ISIR) Osaka University, 8-1, Mihogaoka, Ibaraki, Osaka 567-0047, Japan § JST, ACT-C, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan S Supporting Information *
ABSTRACT: A convenient method for the syntheses of dibenzo[h,rst]pentaphenes and dibenzo[fg,qr]pentacenes via the rutheniumcatalyzed chemoselective C−O arylation of 1,4- and 1,5-dimethoxyanthraquinones is described. Dimethoxyanthraquinones reacted selectively with arylboronates at the ortho C−O bonds to give diarylation products. An efficient two-step procedure consisting of a Corey−Chaykofsky reaction and subsequent dehydrative aromatization afforded derivatives of dibenzo[h,rst]pentaphenes and dibenzo[fg,qr]pentacenes. Hole-transporting characteristics were observed for a device with a bottom-contact configuration that was fabricated from one of these polycyclic aromatic hydrocarbons.
C
Scheme 1. Projected Synthetic Routes of PAHs 1 and 2
onsiderable interest has developed regarding the use of polycyclic aromatic hydrocarbons (PAHs) as organic semiconductors because these compounds have unique properties as electronic and optical materials, including being lightweight and highly flexible.1 A variety of PAHs have been synthesized for this purpose, and their properties have been investigated. The classes of PAHs that have been extensively studied include those containing linearly fused aromatic rings2 such as acenes and phenacenes and those possessing two-dimensionally extended πsystems3−6 such as perylenes, pyrenes, and coronenes. Further expansion of the π-systems by the synthesis of benzo-fused versions of PAH cores has also been explored.2,3 We have been studying catalytic arylations of unreactive C−H,7 C−O,8 and C−N9 bonds in aromatic ketones with arylboronates and have applied these reactions to the concise synthesis of substituted linearly fused PAHs such as anthracenes, pentacenes, dibenzoanthracenes, and picenes.10 Anthraquinone was used as a template for the syntheses of highly substituted acenes, and C−H/ C−O functionalization at all four ortho positions of the carbonyl groups was the key step.10a,c Catalytic C−O functionalization11 has also been applied to the syntheses of PAH derivatives by other groups such as Campaña et al.12 We envisioned that if the chemoselective arylation of ortho C− OMe bonds in preference to C−H bonds could be achieved for anthraquinone derivatives, the use of an anthraquinone derivative possessing methoxy groups at appropriate positions as substrates would allow us to prepare anthracene derivatives with π-systems expanded toward the desired directions. To pursue this possibility, we chose dibenzo[h,rst]pentaphenes 113 and dibenzo[fg,qr]© 2017 American Chemical Society
pentacenes 214 as our target molecules, because the synthesis and electronic properties for these compounds have received limited attention. The projected synthetic routes are shown in Scheme 1. The chemoselective C−O arylation of 1,4-dimethoxyanthraquinone (3) with arylboronate 4 using RuH2(CO)(PPh3)3 (5) as a catalyst would be expected to give 1,4-diarylanthraquinone 6, Received: June 2, 2017 Published: July 13, 2017 3791
DOI: 10.1021/acs.orglett.7b01666 Org. Lett. 2017, 19, 3791−3794
Letter
Organic Letters
hydride at room temperature for 1 h gave the corresponding diepoxide 9a.15 The screening of various Lewis acid catalysts showed that InCl316 was effective for the dehydrative aromatization of 9a to give 3,12-dimethyldibenzo[h,rst]pentaphene 1a (38% yield from 6a) (eq 2). After examining the reaction
which could then be converted into 1 in a short sequence taking advantage of the presence of carbonyl groups. Similarly, 1,5dimethoxyanthraquinone (7) could be transformed into 2. While 1 can be seen as a benzo-fused version of pentaphene or pyrene, 2 may be regarded as a benzo-fused pentacene or a perylene derivative. We report herein the convenient syntheses of PAHs 1 and 2 using the Ru-catalyzed chemoselective C−O arylation of dimethoxyanthracenes with arylboronates. An efficient two-step procedure for converting the diarylated anthraquinones to 1 and 2 was also established. The C−O arylation of 1,4-dimethoxyanthraquinone (3) was first examined. The reaction of 3 with 2.5 equiv of 4methylphenylboronate 4a in the presence of 10 mol % of catalyst 5 in refluxing toluene for 10 h proceeded chemoselectively and afforded 1,4-diarylanthraquinone 6a in 75% isolated yield (Table 1, entry 1). The reaction proceeds smoothly with arylboronates
conditions, 1a was obtained in 40% yield from 6a by using DMSO/THF as a solvent at 50 °C for the epoxide formation and conducting the dehydrative aromatization without purifying epoxide 9a by silica gel column chromatography, which could have caused the partial degradation of 9a (Table 2, entry 1). This
Table 1. Ruthenium-Catalyzed Chemoselective C−O Arylation of 1,4-Dimethoxyanthraquinone (3)a
Table 2. Two-Step Conversion of 1,4-Diarylanthraquinones 6 to Dibenzo[h,rst]pentaphenes 1a
entry
4
R
6
yield (%)
1 2 3 4 5 6 7
4a 4b 4c 4d 4e 4f 4g
Me n-C6H13 n-C12H25 i-Pr i-Bu O(n-C6H13) O(n-C12H25)
6a 6b 6c 6d 6e 6f 6g
75 85 78 72 89 74 85
a
Reaction conditions: 3 (1 equiv), 4 (2.5 equiv), 5 (10 mol %), toluene (5 mL per 1 mmol of 3), 120 °C, 10 h.
entry
6
R
1
yield of 1 (%, from 6)
1 2 3b 4 5 6c 7
6a 6b 6c 6d 6e 6f 6g
Me n-C6H13 n-C12H25 i-Pr i-Bu O(n-C6H13) O(n-C12H25)
1a 1b 1c 1d 1e 1f 1g
40 60 12 42 47 17 48
a Reaction conditions: 6 (0.3 mmol), Me3SI (3 mmol), NaH (4.5 mmol), DMSO (6 mL), THF (6 mL), 50 °C, 1 h, then InCl3 (0.036 mmol), 1,2-dichloroethane (DCE) (7.5 mL), reflux, 12 h. bThe Corey−Chaykovsky reaction was performed at rt. cThe Corey− Chaykovsky reaction was performed for 30 min.
bearing various para substituents such as 4-n-hexyl- (4b), 4-ndodecyl- (4c), 4-iso-propyl- (4d), 4-iso-butyl- (4e), 4-n-hexyloxy(4f), and 4-n-dodecyloxy (4g) groups to give the corresponding 1,4-diarylanthraquinones 6b-g in 72−89% yields (entries 2−7). The C−O arylation of 3 also proceeds with 2-thienylboronates 4h and 4i, and the corresponding dithienylanthraquinones 6h and 6i were obtained in 54% and 55% yields, respectively, when 20 mol % of catalyst 5 was used (eq 1).
protocol was then applied to various 1,4-diarylanthraquinones, and the corresponding dibenzo[h,rst]pentaphenes 1b−g were produced in 12−60% isolated yields from 6b−g (Table 2, entries 2−7).17 The synthesis of thiophene-containing dibenzo[h,rst]pentaphene analogs was examined using similar transformations. In this case, the use of InCl3 as a catalyst for the dehydrative aromatization was not successful, and SnCl2 was found to be a superior catalyst. The two-step protocol from 6h using SnCl2 gave a 13% yield of 1h (eq 3). Similarly, n-hexyl derivative 1i was obtained in 6% yield from 6i. The thiophene-containing dibenzo[h,rst]pentaphene core found in 1h and 1i without further π-extension has not been reported. The three-step synthetic strategy for 1 was then applied to the preparation of dibenzo[fg,qr]pentacene derivatives 2 using 1,5dimethoxyanthraquinone (7) as a substrate (Table 3). The C−O arylation of 7 with arylboronates 4a,b,f,i provided the corresponding 1,5-diarylated anthraquinones 8a,b,f,i in 50−
The conversion of 1,4-diarylanthraquinone 6 to PAH derivative 1 was then examined. A survey of various methods revealed that the use of Corey−Chaykovsky reaction and dehydrative aromatization successfully gave the desired PAH derivative 1. The reaction of 6a with trimethylsulfonium iodide and sodium 3792
DOI: 10.1021/acs.orglett.7b01666 Org. Lett. 2017, 19, 3791−3794
Letter
Organic Letters
Table 3. Synthesis of Dibenzo[fg,qr]pentacenes 2 from 1,5Diarylanthraquinones 7a
entry
4
Lewis acid
temp (°C)
8, yield (%)
2, yield (%)
1 2b 3 4c
4a 4b 4f 4i
InCl3 InCl3 InCl3 SnCl2
reflux reflux reflux 60
8a, 64 8b, 68 8f, 80 8i, 50
2a, 55 2b, 38 2f, 48 2i, 19
Figure 1. Crystal structure of 1b. (a) Top view. (b) Side view. The n-hexyl groups are omitted for clarity.
Figure 2. Crystal structure of 2b. (a) The ORTEP drawing at a 50% probability. H atoms are omitted for clarity. (b) Top view. (c) Side view. In (b) and (c), the n-hexyl groups are omitted for clarity.
a
Reaction conditions (7 to 8): 7 (1 equiv), 4 (2.5 equiv), 5 (10 mol %), toluene (5 mL per 1 mmol of 7), 120 °C, 10 h. Reaction conditions (8 to 2): 8 (0.3 mmol), Me3SI (3 mmol), NaH (4.5 mmol), DMSO (6 mL), THF (6 mL), 50 °C, 1 h, then a Lewis acid (0.036 mmol), 1,2-dichloroethane (DCE) (7.5 mL), reflux, 12 h. bThe Corey−Chaykovsky reaction was performed at rt. cThe C−O arylation was performed for 20 h using 20 mol % of 5.
68% yields. The subsequent Corey−Chaykovsky reaction to form diepoxides 10a,b,f,i, followed by Lewis acid catalyzed dehydrative aromatization gave the desired dibenzo[fg,qr]pentacene derivatives 2a,b,f and the thiophene-containing analog 2i in 19−55% yields. The crystal structures of dibenzo[h,rst]pentaphene 1b and dibenzo[fg,qr]pentacene 2b were obtained by X-ray diffraction analysis. In the crystal of 1b, all of the molecules are aligned in parallel and partially π-stacked in a columnar manner, while each molecule points in the opposite direction from the two neighboring molecules in the column (Figure 1). The interplanar distances of the molecules in a column are 3.43 and 3.52 Å. In contrast, dibenzo[fg,qr]pentacene 2b adopts a herringbone structure in which the tilt angle is 75.1° (Figure 2). The interplanar distances of 2b (3.32 and 3.30 Å) were slightly shorter than those of 1b. Disubstituted dibenzo[h,rst]pentaphenes (1) are predicted to exhibit good OFET properties.14 Theoretical calculations by the DFT method at the B3LYP/6-31G(d,p) level suggest that the highest occupied molecular orbital (HOMO) of 1a is delocalized over the molecular surface (Figure 3a) and the HOMO level of 1a was estimated to be −5.07 eV, which is a suitable level to serve as an active material for p-type OFETs. We chose 1b, instead of 1a, for
Figure 3. (a) HOMO surface of 1a. (b) Transfer characteristics of OFET based on 1b at a drain voltage of −100 V. (c) (a) XRD data and (d) AFM image of 1b film on HMDS-modified SiO2.
examining the OFET properties due to their solubility in chlorobenzene. On the basis of the packing diagram in Figure 1, the intermolecular transfer integral for 1b between HOMOs of πstacked molecules was estimated to be 77 meV using PW91/TZP, as implemented in the Amsterdam Density Functional (ADF) program. This result suggests that 1b has hole-transport characteristics along the π-stacked direction. The OFET performance of 1b was evaluated by employing the bottom-gate bottomcontact configuration. The active layer was prepared on hexamethyldisilazane (HMDS)-modified SiO2/Si substrates by spin-coating from a 1.0 wt % chlorobenzene solution. This 3793
DOI: 10.1021/acs.orglett.7b01666 Org. Lett. 2017, 19, 3791−3794
Letter
Organic Letters
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compound showed typical p-type characteristics, and the hole mobility was found to be 1.4 × 10−3 cm2 V−1 s−1 with an on/off current ratio of 106 and a threshold voltage of −15 V. Its transfer characteristics are shown in Figure 3b. The structural order of 1b in the film state was investigated by X-ray diffraction (XRD) measurements. As shown in Figure 3c, this film displayed a clear diffraction peak, indicating that 1b forms a crystalline structure in thin films. The peak at 2θ = 3.7° corresponds to a d-spacing of 23.9 Å, which is almost equal to the molecular length along the long axis (25.9 Å). This indicates that 1b is aligned in an edge-on orientation on the SiO2 substrate. This is favorable for carrier transport in OFETs. On the other hand, the atomic force microscopy (AFM) image of 1b film showed the presence of large crystalline grains that were several micrometers in size and observable grain boundaries, resulting in moderate hole mobility. In conclusion, we report a convenient synthetic method for preparing dibenzo[h,rst]pentaphenes (1), dibenzo[fg,qr]pentacenes (2), and their thiophene-containing analogs by the ruthenium-catalyzed coupling of 1,4- (3) and 1,5-dimethoxyanthraquinone (7) with aryl- and thienylboronates. The crosscoupling proceeded selectively at the C−O bonds in the anthraquinones to give the corresponding 1,4- and 1,5-diarylated anthraquinones. Transformations of the carbonyl groups in the diarylated anthraquinones to epoxides by the Corey−Chaykovsky reaction, followed by a Lewis acid catalyzed dehydrative aromatization, resulted in the production of 1 and 2. Compound 1b, when fabricated on OFET devices with a bottom-contact configuration, exhibited hole-transporting characteristics.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.7b01666. Full experimental details, characterization data of all new compounds, and X-ray crystallographic data for 1b and 2b (PDF) Crystallographic data for 1b and 2b (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Fumitoshi Kakiuchi: 0000-0003-2605-4675 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported in part by JSPS KAKENHI Grant Numbers JP15H05839 in Middle Molecular Strategy, and CREST and ACT-C (Grant Number JPMJCR12Y8) from the Japan Science and Technology Agency (JST), Japan. T.K. is also grateful for support by JSPS KAKENHI Grant Number 16H01040 (Precisely Designed Catalysts with Customized Scaffolding). Dedicated to Professor Teruaki Mukaiyama in celebration of his 90th birthday (Sotsuju).
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NOTE ADDED AFTER ASAP PUBLICATION Reference 14 was updated on July 21, 2017.
REFERENCES
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DOI: 10.1021/acs.orglett.7b01666 Org. Lett. 2017, 19, 3791−3794
