Exclusive Formation of Bridge-Substituted [2.2]Paracyclophane by

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Exclusive Formation of Bridge-Substituted [2.2]Paracyclophane by Topochemical Photocycloaddition Reaction of Unsymmetrical Substituted p‑Quinodimethane Takahito Itoh,*,† Fumiaki Kondo,† Takahiro Uno,† Masataka Kubo,† Norimitsu Tohnai,‡ and Mikiji Miyata⊥ †

Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurimamachiya-cho, Tsu-shi, Mie 514-8507, Japan ‡ Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan ⊥ The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan S Supporting Information *

ABSTRACT: Unsymmetrical 7-(2′-bromoethoxycarbonyl)7,8,8-tris(methoxycarbonyl)-p-quinodimethane (2) underwent a quantitative intermolecular [6 + 6] photocycloaddition reaction through a single crystal-to-single crystal transformation to afford a bridge-substituted [2.2]paracyclophane (3). The crystal structure of 2 indicates that the bromoethoxy groups conveniently form σhalogen bonds with the carboxyl groups to yield 2-fold helical assemblies of an isolated pair of 2. 3 has a relatively long distance between bridged carbon−carbon bonds in comparison with the known ones. Such bonds caused an one-side insertion reaction of molecular oxygen in solution to afford the peroxide bridgesubstituted [2.2]paracyclophane in a quantitative yield.

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tris(methoxycarbonyl)-p-quinodimethane (2) was designed and attempted for the polymerization. Surprisingly, crystals of 2 did not afford its polymer, but afforded exclusively bridgesubstituted [2.2]paracyclophane (3) by a solid-state photochemical reaction (Figure 1(iv)). To our knowledge, this is the first example of [6 + 6] photocycloaddition reaction in the solid state, compared to well-known [2 + 2] and [4 + 4] photocycloaddition reactions in the solid states.36−45 This article reports quantitative conversion of 2 to 3 by topochemical [6 + 6] photocycloaddition reaction based on the specified molecular arrangement. X-ray crystallographic analysis indicates that this interesting behavior is ascribed to the formation of 2-fold helical assemblies of an isolated pair of 2 through interaction between the σ-hole of bromine atom and the oxygen atom of carbonyl group (Br···OC) in crystals. 2 was synthesized by the Knoevenagel condensation of 4[di(methoxycarbonyl)methylene]cyclohexanone (4) with 2bromoethyl methyl malonate using titanium tetrachloride and pyridine as a dehydrating system to give 1-[(2′-bromoethoxycarbonyl) (methoxycarbonyl)methylene]-4-[di(methoxycarbonyl)methylene]cyclohexane (5) (54% yield). Oxidation of 5 with activated manganese dioxide in benzene

oncovalent intermolecular interactions play an important role not only for functional biomolecules such as DNA and proteins but also for designed supramolecules.1−4 In addition to the usual hydrogen bonds,5,6 various weak interactions such as halogen bonds,7−9 π−π and CH−π interactions10,11 have been widely examined. The resulting specified molecular arrangements led to unique solid-state cycloaddition reactions12−14 and polymerization reactions.15−19 So far, we have studied supramolecular crystals of pquinodimethane derivatives to acquire specified arrangements and reactions. As shown in Figure 1, the crystals of symmetrically substituted ones brought us notable results: (i) 7,7,8,8-tetrakis(methoxycarbonyl)-p-quinodimethane (1a)20,21 for 1,6-trans-type topochemical polymerization through a slide-parallel mode by the interaction (HC−H···OC), (ii) 7,7,8,8-tetrakis(2′-bromoethoxycarbonyl)-p-quinodimethane (1b)22 for 1,6-trans-type topochemical single crystal-to-single crystal polymerization through a slide-parallel mode by the halogen bonds (Br···Br and HC-H···Br), and (iii) 7,7,8,8tetrakis(ethoxycarbonyl)-p-quinodimethane (1c)23,24 for cisaddition reaction of molecular oxygen with alternating copolymerization through a 2-fold rotation parallel mode by the interaction (HC−H···OC), respectively. Such a research directed us to unsymmetrical substituted pquinodimethanes toward asymmetric-induced polymerizations.25−35 Among them, 7-(2′-bromoethoxycarbonyl)-7,8,8© XXXX American Chemical Society

Received: April 24, 2017 Revised: June 9, 2017

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DOI: 10.1021/acs.cgd.7b00580 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Figure 1. Crystalline supramolecules and reactions of p-quinodimethane derivatives: (i) 1,6-trans-type polymerization of 1a, (ii) 1,6-trans-type polymerization of 1b, (iii) cis-addition alternating copolymerization of 1c with molecular oxygen, and (iv) photocycloaddition reaction of 2 in the present study.

at reflux afforded 2 (21% yield), which was recrystallized from a mixture of benzene and hexane to afford a yellow columnar crystal. Crystals of 2 were subjected to reaction in vacuo by irradiation with a high-pressure Hg lamp at 30 °C. When yellow crystal 2 was exposed to UV light at 30 °C for 12 h, the yellow columnar crystal faded to afford a white one with retaining initial crystal shape in appearance in a quantitative yield (Figure 2).

Figure 3. X-ray powder diffraction patterns of (a) crystal 2 and (b) white crystal after UV irradiation.

(Supporting Information). Single crystals of 2 suitable for Xray structure determination were obtained by recrystallization from a mixture of benzene and hexane (5.5/4.5 v/v). The yellow color of single columnar crystal 2 faded completely within 1 min after direct UV irradiation to crystal 2 at 296 K, indicating that the photoreaction in a single crystal took place at a faster speed. The molecular packings of crystal 2 and white crystal are shown in Figure 4. Crystal 2 belongs to the space group of P21/c (No. 14) and has monoclinic unit cell with a = 7.7080(2), b = 18.0002(6), c = 13.6100(4) Å, and β = 92.3150(15)°, where four molecules are included. The reacting molecules, which are related by the center of inversion, make a pair, where the molecules are arranged parallel to each other in a head-to-tail orientation, and also a pair of reacting molecules is isolated from the neighboring pairs. Moreover, the molecules form a 2-fold helical assemblies along the b-axis direction through a weak halogen bond (3.33 Å) between the σ-hole of bromine atom and the oxygen atom of the carbonyl group (Figure 4a,c). The distance of exomethylene carbons between a pair of reacting molecules is 3.88 Å, which is within a distance (3.5−4.2 Å) topochemically allowed for [2 + 2] photocycloaddition in the solid state14 and the distance (about 4 Å) suitable for topochemical polymerization of the substituted p-quinodimethanes.20,21 White crystal obtained by UV irradiation belongs to the space group P21/c (No. 14), which is same for that of crystal 2, and has a monoclinic unit cell with a = 8.1443(8), b = 16.908(3), c = 12.8583(17) Å, and β =

Figure 2. Photographs of (a) crystal 2 and (b) white crystal after UV irradiation.

White crystal after UV irradiation was dissolved in THF to determine its molecular weight by gel permeation chromatography (GPC) measurement (Supporting Information). Crystal 2 showed a peak at the molecular weight of 410, and white crystals showed only a sharp peak with a molecular weight of 600, and peaks of unreacted crystal 2 and a product with higher molecular weight than 600 were not observed. This indicates that the white crystals are not oligomers and polymers of 2, but a pure product with molecular weight close to a dimer of 2. X-ray powder diffraction (XRD) patterns of crystal 2 and white crystal after UV irradiation are shown in Figure 3. The reaction product showed a very sharp diffraction pattern, indicating that high crystallinity is maintained during the photoreaction; that is, the reaction proceeds through crystal-tocrystal transformation. To determine a chemical structure of white crystal, we investigated crystal structures of crystal 2 and white crystal after direct UV irradiation by X-ray crystallographic analysis B



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Figure 4. Molecular packing structures along the b-axis and 21 axes of (a) crystal 2 and (b) white crystal after direct UV irradiation, and along the caxis on glide planes of (c) crystal 2 and (d) white crystal. An exomethylene carbon distance (dcc = 3.88 Å) and a halogen bond (Br···OC, 3.33 Å) between neighboring molecules, and the ethylene bridge distance (1.68 Å) in white crystal are shown.

Figure 5. Spectral changes in 1H NMR and 13C NMR spectra in chloroform-d at air exposure times of 0, 16, and 54 h.

Scheme 1. Reaction of 3 with Molecular Oxygen in Solution

92.775(10)°, where two molecules are included. X-ray crystallographic analysis indicates obviously the formation of the bridge-substituted [2.2]paracyclophane (3) (1,9-bis(2′bromoethoxycarbonyl)-1,2,2,9,10,10-hexa(methoxycarbonyl) [2.2]paracyclophane) (Figure 4b), which was also confirmed by 1 H NMR, 13C NMR, IR, and MS spectroscopies and elemental analysis. In the crystal structure of 3, the σ-halogen bonds between bromine atoms and oxygen ones of carbonyl groups observed in crystal 2 disappear, and bromine atoms of bromoethoxy groups are taken into a space generated by neighboring three methyl groups due to a rotation of bromoethoxy groups. Moreover, one-dimensional columns of

achiral molecular assemblies by the glide plane symmetry operation are formed along the c-axis (Figure 4c,d). Exclusive product 3 is considered to be formed through an intermolecular [6 + 6] photocycloaddition reaction of crystal 2. [2 + 2] and [4 + 4] photocycloaddtiton reactions in the solids state are wellknown, but [6 + 6] photocycloaddition reaction in the solid state is the first example to our knowledge. Changes in the lattice lengths and the volume on the photochemical reaction from crystal 2 to crystal 3 are +5.7%, −6.1%, and −5.5% for the a-axis, b-axis, and c-axis, respectively, and −6.3% for the volume, and these changes are relatively small. Therefore, it is C



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considered that such small changes allow a single crystal-tosingle crystal transformation. When 3 was dissolved in chloroform-d and the resulting solution was placed in an open air for a long time, we noticed that their spectral changes in the 1H NMR and 13C NMR charts took place. New peaks at 7.20, 6.98, and 6.91 ppm in the 1H NMR spectrum and at 89.5 and 89.3 ppm and 72.1 and 71.9 ppm in the 13C NMR spectrum appeared and increased slowly with air exposure time. The spectral changes of the aromatic region (7.4−6.0 ppm) in the 1H NMR spectrum and of the side-chain quaternary carbon region (70−93 ppm) in the 13C NMR spectrum with air exposure time are shown in Figure 5. The quaternary carbons of the side-chain at 74.3 and 74.1 ppm in the 13C NMR spectrum decreased with air exposure time, but new peaks at 89.5 and 89.3 ppm and 72.1 and 71.9 ppm increased. Previously, we reported that quaternary carbons (−C(COOEt)2−O-O−) of an alternating copolymer of 1c with molecular oxygen appear at 89.4 ppm.23,24 Therefore, new peaks at 89.5 and 89.3 ppm are assigned to quaternary carbons next to oxygen atom, indicative of the formation of peroxide bridge-substituted [2.2]paracyclophane by the reaction of 3 with molecular oxygen (Scheme 1). After complete reaction with molecular oxygen, reaction product was isolated as white crystals in a quantitative yield. The peroxide bridge-substituted [2.2]paracyclophane formation was also confirmed by the reaction of 3 with oxygen gas in benzene and by 1H NMR, 13C NMR, IR, and MS spectroscopies and elemental analysis. As we obtained successfully 3, it was compared with [2.2]paracyclophane in the viewpoint of the chemical structure. The molecular structure of 3 viewed along the phenylene planes is shown in Figure 6, and their parameters are summarized in Table 1, together with corresponding ones of [2.2]paracyclophane.46,47

The intramolecular nonbonded distance (c) between the para carbon atoms is 2.73 Å. The intramolecular separation (d) between the central carbon atoms of the two benzene rings is 2.92 Å as well as the corresponding one (3.09 Å) of [2.2]paracyclophane, which is considerably shorter than the normal van der Waals separation between parallel benzene rings (3.4 Å). The para carbon atoms bend 12.40° (α) and 10.40° (α′), respectively, out of the least-squares planes formed by four carbon atoms in each of the facing benzene rings. The bond length (b) (1.68 Å) of the ethylene bridge carbons is a little longer than that (1.59 Å) in [2.2]paracyclophane. Moreover, the torsion angle about the ethylene bridge carbons (δ) (12.34°) is larger than that (6°) of [2.2]paracyclophane. These differences may come from the presence of four substituents because the bond length (b) of the ethylene bridge becomes longer than that of [2.2]paracyclophane (0.09 Å) in order to minimize steric repulsion between the substituents on the ethylene bridge carbons and to induce reduction in electron density on the ethylene bridge bond by electron-accepting ester groups. The longer length of d and the greater angles of α, β, and γ in 3 indicate that it has a larger strained energy caused by sterically constrained structure and a torsion about two ethylene bridge carbons caused by a deformation of benzene rings in comparison with that of [2.2]paracyclophane. This larger strained energy facilitates the reaction of 3 with molecular oxygen to afford a peroxide bridgesubstituted [2.2]paracyclophane, in contrast to addition reactions of molecular oxygen into the benzene moiety of benzo[2.2]paracyclophane,48 [2.2]paracyclophane-1,9-diene,49 and [2.2.2.2](1,2,4,5)cyclophane.50 In conclusion, unsymmetrical 2 underwent a quantitative intermolecular [6 + 6] photocycloaddition reaction through a single crystal-to-single crystal transformation to afford 3. The crystal structure of 2 indicated that σ-halogen bonds between the bromine atoms of bromoethoxy groups and oxygen ones of the carbonyl groups effectively exert the formation of 2-fold helical assemblies of an isolated pair of 2. The insertion reaction of molecular oxygen into the strained bridge bonds of 3 occurred to afford a peroxide bridge-substituted [2.2]paracyclophane in a quantitative yield.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.7b00580.

Figure 6. Molecular structure of 3.

Experimental procedures, synthesis procedure, characterization of all new compounds (PDF)

Table 1. Bond Lengths, Angles, and Intermolecular Nonbonded Distances of 3 and [2.2]Paracyclophane compounds

3

[2.2]Paracyclophane46,47

a (Å) a′ (Å) b (Å) c (Å) d (Å) α (deg) α′ (deg) β (deg) β′ (deg) γ (deg) γ′ (deg) δ (deg)

1.54 1.53 1.68 2.73 2.92 12.40 10.40 10.03 8.35 110.48 108.80 12.34

1.51

Accession Codes

CCDC 1528452−1528453 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

1.59 2.78 3.09 12.6

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AUTHOR INFORMATION

Corresponding Author

113.7

*E-mail: [email protected]. ORCID

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Takahito Itoh: 0000-0002-8613-5699 D



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Notes

(35) Itoh, T.; Tachino, K.; Akira, N.; Uno, T.; Kubo, M.; Tohnai, N.; Miyata, M. Macromolecules 2015, 48, 2935−2947. (36) Woodward, R. B.; Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1969, 8, 781−853. (37) Ramamurthy, V.; Venkatesan, K. Chem. Rev. 1987, 87, 433−481. (38) Hasegawa, M.; Maekawa, Y.; Kato, S.; Saigo, K. Chem. Lett. 1987, 16, 907−910. (39) Maekawa, Y.; Kato, S.; Hasegawa, M. J. Am. Chem. Soc. 1991, 113, 3867−3872. (40) MacGillivray, L. R.; Reid, J. L.; Ripmeester, J. A. J. Am. Chem. Soc. 2000, 122, 7817−7818. (41) Coates, G. W.; Dunn, A. R.; Henling, L. M.; Ziller, J. W.; Lobkovsky, E. B.; Grubbs, R. H. J. Am. Chem. Soc. 1998, 120, 3641− 3649. (42) Liu, J.; Wendt, N. L.; Boarman, K. J. Org. Lett. 2005, 7, 1007− 1010. (43) Kohmoto, S.; Ono, Y.; Masu, H.; Yamaguchi, K.; Kishikawa, K.; Yamamoto, M. Org. Lett. 2001, 3, 4153−4155. (44) Yamada, S.; Kawamura, C. Org. Lett. 2012, 14, 1572−1575. (45) Khatri, B. B.; Vrubliauskas, D.; Sieburth, S. M. Tetrahedron Lett. 2015, 56, 4520−4522. (46) Hope, H.; Bernstein, J.; Trueblood, K. N. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1972, 28, 1733−1743. (47) Vögtle, F. Cyclophane Chemistry, Synthesis, Structures and Reactions; John Wiley & Sons: New York, 1993; pp 57−216. (48) Wasserman, H. H.; Keehn, P. M. J. Am. Chem. Soc. 1972, 94, 298−300. (49) Erden, I.; Gölitz, P.; Näder, R.; de Meijere, A. Angew. Chem., Int. Ed. Engl. 1981, 20, 583−585. (50) Gray, R.; Boekelheide, V. J. Am. Chem. Soc. 1979, 101, 2128− 2136.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research is partially supported by a Grant-in-Aid for Scientific Research (No. 15K05518) from JSPS, Japan. REFERENCES

(1) Lehn, J. -M. Science 1985, 227, 849−856. (2) Vögtle, F. Supramolecular Chemistry: An Introduction; John Wiley & Sons: Chichester, 1989. (3) Lehn, J. -M. Supramolecular Chemistry; Concepts and Perspectives; Wiley-VHC: Weinheim, 1995. (4) Desiraju, G. R.; Vittal, J. J.; Ramanan, A. Crystal Engineering; World Scientific Publishing: Singapore, 2011. (5) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford University Press: Oxford, 1997. (6) Aakeröy, C. B.; Seddon, K. R. Chem. Soc. Rev. 1993, 22, 397−407. (7) Dumas, J. M.; Gomel, M.; Guerin, M. In The Chemistry of Functional Groups, Supplement D; Patai, S., Rappoport, Z. Eds.; John Wiley & Sons: New York, 1983; pp 985−1020. (8) Metrangolo, P.; Resnati, G. Chem. - Eur. J. 2001, 7, 2511−2519. (9) Priimagi, A.; Cavallo, G.; Metrangolo, P.; Resnati, G. Acc. Chem. Res. 2013, 46, 2686−2695. (10) Nishio, M.; Hirota, M.; Umezawa, Y. The CH/π Interaction. Evidence, Nature, and Consequences; Wiley-VCH: New York, 1998. (11) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond: In Structural Chemistry and Biology; Oxford University Press: Oxford, 1999. (12) Kearsley, S. K. in Organic Solid State Chemistry, Desiraju, G. R., Ed.; Elsevier: New York, 1987; pp 69−115. (13) Ramamurthy, V.; Venkatesan, K. Chem. Rev. 1987, 87, 433−481. (14) Schmidt, G. M. J. Pure Appl. Chem. 1971, 27, 647−678. (15) Dilling, W. L. Chem. Rev. 1983, 83, 1−47. (16) Hasegawa, M. Adv. Phys. Org. Chem. 1995, 30, 117−171. (17) Matsumoto, A.; Odani, T. Macromol. Rapid Commun. 2001, 22, 1195−1215. (18) Matsumoto, A. Polym. J. 2003, 35, 93−121. (19) Lauher, J. W.; Fowler, F. W.; Goroff, N. C. Acc. Chem. Res. 2008, 41, 1215−1229. (20) Itoh, T.; Nomura, S.; Uno, T.; Kubo, M.; Sada, K.; Miyata, M. Angew. Chem., Int. Ed. 2002, 41, 4306−4309. (21) Nomura, S.; Itoh, T.; Nakasho, H.; Uno, T.; Kubo, M.; Sada, K.; Inoue, K.; Miyata, M. J. Am. Chem. Soc. 2004, 126, 2035−2041. (22) Itoh, T.; Nomura, S.; Nakasho, H.; Uno, T.; Kubo, M.; Tohnai, N.; Miyata, M. Macromolecules 2015, 48, 5450−5455. (23) Nomura, S.; Itoh, T.; Ohtake, M.; Uno, T.; Kubo, M.; Kajiwara, A.; Sada, K.; Miyata, M. Angew. Chem., Int. Ed. 2003, 42, 5468−5472. (24) Itoh, T.; Nomura, S.; Ohtake, M.; Yoshida, T.; Uno, T.; Kubo, M.; Kajiwara, A.; Sada, K.; Miyata, M. Macromolecules 2004, 37, 8230− 8238. (25) Natta, G.; Porri, L.; Valenti, S. Makromol. Chem. 1963, 67, 225− 228. (26) Farina, M.; Audisio, G.; Natta, G. J. Am. Chem. Soc. 1967, 89, 5071−5071. (27) Miyata, M.; Takemoto, K. Polym. J. 1977, 9, 111−112. (28) Addadi, L.; Lahav, M. J. Am. Chem. Soc. 1978, 100, 2838−2844. (29) Addadi, L.; Lahav, M. J. Am. Chem. Soc. 1979, 101, 2152−2156. (30) Addadi, L.; Lahav, M. Pure Appl. Chem. 1979, 51, 1269−1284. (31) Addadi, L.; Van Mil, J.; Lahav, M. J. Am. Chem. Soc. 1982, 104, 3422−3429. (32) Miyata, M. In Comprehensive Supramolecular Chemistry: Molecular Devices and Applications of Supramolecular Chemistry; Lehn, J.-M. Ed.; Pergamon: Oxford, 1996; pp 557−582. (33) Iizuka, S.; Nakagaki, N.; Uno, T.; Kubo, M.; Itoh, T. Macromolecules 2010, 43, 6962−6967. (34) Nagai, T.; Uno, T.; Kubo, M.; Itoh, T. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 466−479. E


Exclusive Formation of Bridge-Substituted [2.2]Paracyclophane by

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