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Synthesis and Characterization of Hexapole [7]Helicene, A Circularly Twisted Chiral Nanographene Yanpeng Zhu, Zeming Xia, Zeying Cai, Ziyong Yuan, Nianqiang Jiang, Tao Li, Yonggen Wang, Xiaoyu Guo, Zhihao Li, Shuang Ma, Dingyong Zhong, Yang Li, and Jiaobing Wang J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b01447 • Publication Date (Web): 14 Mar 2018 Downloaded from http://pubs.acs.org on March 14, 2018
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Journal of the American Chemical Society
Yanpeng Zhu*, Zeming Xia*, Zeying Cai+, Ziyong Yuan*, Nianqiang Jiang*, Tao Li*, Yonggen Wang*, Xiaoyu Guo*, Zhihao Li*, Shuang Ma*, Dingyong Zhong+, Yang Li±, Jiaobing Wang * *
School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, China
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School of Physics, Sun Yat-Sen University, Guangzhou 510275, China
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Instrumental Analysis and Research Center, Sun Yat-Sen University, Guangzhou 510275, China
Supporting Information Placeholder ABSTRACT: We report the synthesis and characterization of two hexapole [7]helicenes (H7Hs). Single crystal X-ray diffraction unambiguously confirms the molecular structure. H7H absorbs light, with distinct Cotton effect, from ultraviolet to the near infrared (λmax = 618 nm). Cyclic voltammetry reveals nine reversible redox states, consecutively from -2 to +6. These chiroptical and electronic properties of H7H are inaccessible from helicene’s small homologues.
Since the first synthesis and resolution of [6]helicene by Newman in the 1950s,1 helicene has received considerable attention due to its unusual distorted structure and attractive chiroptical and electronic properties.2 However, it can be expected that the synthesis and characterization of higher [n]helicenes would be increasingly challenging, because it is difficult to stitch together multiple ortho-fused phenyl rings in a controlled manner along an extended helical arrangement. This envision is reinforced by the fact that it took 60 years for the field to evolve from [6]helicene,1 composed of 26 conjugated carbon atoms (26-C), to the 66-C higher-homologue, [16]helicene.3 In addition, an oxa[19]helicene has been documented very recently.4 In contrast to the [n]helicenes, the synthesis of multiple helicenes has recently witnessed a rapid development.5-9 Taking advantages of the flexible synthetic approaches, various multiple helicenes, such as quintuple [6]Helicene8 and hexapole [5]helicenes,9d, 9e have been prepared, which provide new opportunity in exploring chiral conjugated compounds, and may prove useful in materials science as the curved synthetic nanographenes.10,11 Herein, we report the synthesis and characterization of the first hexapole [7]helicene (H7H, Figure 1), which embeds six [7]helicenes in a propeller-shaped structure and comprises 150 conjugated carbon atoms. H7H was characterized using matrixassisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS), nuclear magnetic resonance (NMR) spectroscopy, and single crystal X-ray diffraction. Optically pure H7H was obtained by using chiral high performance liquid chroma-tography (HPLC). It absorbs light, with distinct Cotton effect, covering the whole spectral window from the ultraviolet (UV) to the near infrared (NIR). Moreover, electrochemical techniques identify nine reversible redox states, consecutively from -2 to +6. The rich chiroptical and electronic properties of H7H are
unusual compared with either helicene’s small homologs, or other established optically active nanocarbon compounds and materials, such as chiral fullerenes,12 asymmetric graphene quantum dots,13 and resolved chiral carbon nanotubes.14
Figure 1. Structure and synthesis of H7H. (A) Space-filling molecular models of the H7H enantiomers. (B) Synthetic scheme with different structural subunits and the newly formed C-C bonds labeled. Note, for clarity, both the ter-butyl (blue star) and ether substituents (red star) are removed in the models, which are optimized using molecular mechanics.
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H7H is a carbon-based molecular propeller with six DBP (dibenzo[e,l]pyrene) blades attached to a central HBC (hexabenzo-coronene) core. Both the DBP and HBC subunits are twisted uniformly in a helical manner to meet the steric requirements. In this way, a virtual [7]helicene (Figure 1B, colored in cyan) nests between each two neighboring DBP blades. As a whole, six [7]helicenes are fused together, side by side, circularly around the central helical axis, forming an extremely large chiral π-structure with 150 conjugated carbon atoms. We synthesized two H7H derivatives (H7H1, H7H2), with the same chiral carbon skeleton, from the HPB (hexaphenylbenzene) based polyphenylene precursors15 (P1, P2). As shown in Figure 1B, a cyclotrimerization reaction of the alkyne dirivative 1, or 2, catalyzed by Co2(CO)8,16 afforded the key precursor compound P1, or P2 (yield >90%), which contains 25 phenyl rings organized on a HPB platform. Scholl oxidation of P1, or P2, in the presence of DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone) and MSA (methanesulfonic acid), converted the HPB and TPB (terphenyl benzene) subunits of the precursors into HBC core and DBP blade, respectively, providing the target H7H product. The yield of Scholl oxidation for dehydrocyclization is not high (H7H1 46%, H7H2 18%), but remarkable, considering that 18 C-C bonds are formed in one step to stitch together 25 phenyl rings in a chiral arrangement. Detailed synthesis of H7Hs and the precursors are provided in the supporting information (SI). Currently, it remains unclear whether there is an exact sequence in the 18-fold dehydrocyclization reaction. The reaction did not stop at a specific intermediate state even if insufficient amount of oxidant (e.g. 12 eq. of DDQ) was utilized. According to the literature,9b the Scholl oxidation might initiate from the alkoxylated phenyl rings on the TPB subunit, in which the electron-donating alkoxyl groups facilitate the formation of cationic radical and therefore promote coupling with the neighboring phenyl rings to form new C-C bond. Preorganization of the precursors on a HPB platform is paramount for the successful implementation of the synthesis. It is noteworthy that HPB intrinsically has a dynamic propeller conformation,17 which is expected to guide the dehydrocyclization process, and to be transferred to the propeller-shaped H7H product featuring (M)-, or (P)-form of helicity. In other words, once a C-C bond is formed in the HPB moiety, helical sense of the H7H product is determined. Steric crowding in the polyphenylene precursor prohibits the formation of other potential diastereoisomers.6a
Figure 2. Mass (A) and 1H-NMR (B, in CDCl3) spectra of H7H1. Inset of (A), simulated and measured isotope pattern. MALDI-TOF MS result (Figure 2A) of H7H1 indicates that the Scholl oxidation removes 36 hydrogen atoms from the precursors, agreeing with the expected formation of 18 C-C bonds during the cyclodehydrogenation process. The measured isotope pattern matches that of the simulated one. 1H NMR measurement (Figure 2B) shows four resonance signals appeared in the down-field at 5.9, 7.2, 7.7, and 9.4 ppm, which are assigned to protons H1-H4 (Figure 1B), using a combination of two-dimensional NMR spectroscopic techniques (see SI). Specifically, proton H2, at 5.9 ppm, experiences a strong shielding effect because it sits above the neighboring aromatic DBP blade. In addition, the OCH2-protons of H7H1 manifest a group of two resonance signals (4.3, 4.4 ppm), consistent with its asymmetric environment nearby. Single crystals of H7H2 suitable for X-ray crystallography were grown by slow evaporation of n-hexane into a solution of H7H2 in carbon disulfide. X-ray diffraction data unambiguously discloses the propeller structure of a circularly twisted chiral nanographene (Figure 3, S1, S2), in agreement with the calculated structure (Table S2). Six DBP blades, attached to the HBC core, tilt uniformly at the periphery around the central chiral axis, resulting in the P- or M-form of helicity. The mean plane of each DBP blade and that of the HBC core intersect with an average dihedral angle (DA) of ca. 35°.
Figure 3. X-ray crystal structure of H7H2 (CCDC number: 1563001) with one embedded [7]helicene colored in cyan (A). In each unit cell (B), both enantiomers are deposited, the (M)-, and (P)-form isomers are colored in grey, and blue, respectively. There is no π-π stacking between neighboring H7H2 molecules. Note, for clarity, the ter-butyl and methoxy groups are removed. HOMA values for the representative rings are shown in red.
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Journal of the American Chemical Society Like [7]helicene, the neighboring phenyl rings-iii overlap with each other, and the shortest distance between the opposite carbon atoms is about 3.0 Å, well below the sum of van der Waals radius of two carbon atoms (3.4 Å). The phenyl rings-i, which fuse, and are shared by, the DBP and HBC subunits, are twisted due to steric repulsion with an average torsion angle of 31° along Ce-CbCc-Cf. At the stretched inner edge of the embedded [7]helicene, Cc-Cd bond (average bond length, 1.445 Å) is the most elongated, and the average DA along Ca-Cb-Cc-Cd is found to be 29°. Details on the crystal structure are provided in the SI (Figure S1-2, Table S1-2). To our knowledge, H7H2 is by far the largest conjugated polycyclic nanocarbon compounds, which were ever characterized crystallographically, including the planar, curved, and spherical versions, both chiral and achiral.18 Based on bond lengths in the crystal structure, the local aromaticity of individual rings in H7H2 was evaluated using the harmonic oscillator model of aromaticity (HOMA).19 In general, the HOMA values varies, in an alternating manner, from the center of HBC core to the edge of DBP blade. The new rings, formed by dehydrocyclization (each with one new C-C bond, Figure 1B), shows lower aromaticity than that of the original ones. This result is consistent with the Clar structure of H7H (Figure S3), in which both the HBC and DBP moieties feature a “fully benzenoid” πsystem,20 and altogether 25 aromatic sextets are present.
Figure 4. (A) UV-vis and CD (5.0 µM, in CH2Cl2) spectra of H7H1, inset, chiral HPLC trace of H7H1 (eluent, nhexane/ethanol, 95/5, v/v, UV detector: 300 nm) and a visualized picture of the H7H1 solution. (B) STM image of the resolved (P)H7H1 on a gold substrate. The arrow indicates the direction of the helicity. Exceptionally large conjugated structure of H7H enables it to absorb light from the ultraviolet to the near infrared. The absorption spectrum of H7H shows four major bands at 289, 334, 413, and 618 nm (Figure 4A). The strong absorption around 618 nm (ε = 92000 M-1cm-1) gives the green-cyan color of the H7H solution. H7H has no fluorescence. The electronic characteristic of H7H was rationalized by using density functional theory (DFT)
calculation, which reproduces well the observed absorption features (Figure S4, S5). The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are calculated, at the B3LYP/6-31G (d) level of theory, as -4.35 and -2.34 eV, respectively. Chiral resolution and assignment of the helicity are achieved by using chiral HPLC and scanning tunneling microscopy (STM) in conjunction (Figure S6, S7). A semipreparative SCDP column enables a baseline separation of H7H1 (Figure 4A, inset). Circular dichroism (CD) spectra of the H7H1 enantiomers obtained thereby display a perfect mirror image of each other (Figure 4A). The optically pure H7H1 samples are further utilized for the STM investigation. Disc-shaped nanoscale objects of ca. ~2 nm in width are uniformly deposited on the gold substrate (Figure S7). A zoom-in observation offers more elaborate structure (Figure 4B), which features a six-blade propeller configuration in agreement with the crystal data. The brightness of the lobe,21 which reflects the height of the structural components relative to the substrate, changes unidirectionally around the chiral axis. Thereby, we can assign the helicity of the samples: the second eluted enantiomer of H7H1 ([α]D28 = +500°×c = 0.001; CH2Cl2), which manifests a positive Cotton effect at the wavelength above 420 nm, has a (P)-helicity. A similar method applies to its (M)form enantiomer (Figure S7). The observed CD spectrum and the assignment of helicity are further supported by DFT calculations (Figure S5). H7H has a remarkable thermostability, resisting racemization and decomposition at high temperature. Heating of the optically pure H7H1 at 270 in diphenyl ether in a sealed Schlenk tube for 12 hours under an inert atmosphere does not result in evident change in the 1H-NMR, UV-vis, and CD spectra (Figure S11). DFT calculation resulted in an energy barrier of 52.1 kcal/mol for the isomerization of H7H from the (M,M,M,M,M,M)- to the (P,M,M,M,M,M)-isomer (Figure S12). This energy barrier is higher than the corresponding value of [7]helicene, 42.5 kcal/mol.22
Figure 5. CV (black solid) and DPV (red dash) diagrams of H7H2 (vs Fc*/Fc*+, Fc* = decamethylferrocene) in CH2Cl2. Six reversible oxidation waves are identified at 0.28, 0.46, 0.70, 0.87, 0.94, and 1.05V, respectively. Inset, two reversible reduction waves at the potential of -1.41 and -1.57V. Supporting electrolyte: 0.1 M n-Bu4NPF6. Working electrode: Pt disk. Counter electrode: Pt wire. Reference electrode: Ag/Ag+. Scan rate: 50 mV/s. Note, CV diagrams recorded at different scanning rates support the reversibility of the redox process, see SI. Cyclic voltammetry (CV, Figure 5) of H7H2 in CH2Cl2 shows eight reversible redox waves from -1.57 to 1.05 V (E, all vs Fc*/Fc*+). Differential pulse voltammetry (DPV) confirms the single-electron nature of each redox process. HOMO-LUMO gap calculated from the onset potentials (1.58 eV) agrees with the
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optical gap (1.51 eV), see SI. Compared with the HBC (Eox = 1.02 V)23 and DBP (Eox = 1.07 V, Figure S9) structural subunits, H7H (Eox1 = 0.28 V) displays a significantly enhanced capability to stabilize the oxidized species, due to its extensively conjugated πsystem, in which both the through-bond and through-space24 electron delocalization should exist. In conclusion, we have prepared two 150-C propeller-shaped H7Hs by stitching together 25 phenyl rings of the HPB based polyphenylene precursors under Scholl conditions. The structure of H7H was unambiguously confirmed using single crystal X-ray crystallography. Optically pure H7H displays high thermostability and a wealth of remarkable chiroptical and electronic properties. The readily accessible nanoscale chiral carbon compounds might have broad applications in different fields such as sensors, chiroptical and electronic devices.25
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The Supporting Information is available free of charge on the ACS Publications website. Synthesis, chiral HPLC data, NMR spectra, DFT studies, electrochemical studies, X-ray crystallography data (PDF) Single crystal X-ray diffraction data of H7H2 (CIF)
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[email protected] The authors declare no competing financial interests.
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This research was supported by the 1000 Young Talent Program, the National Natural Science Foundation of China (21372264), the Foundation of Guangzhou Science and Technology (201504010021), and the Program for Changjiang Scholars and Innovative Research Team in University of China (IRT1298).
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(1) Newman, M. S.; Lednicer, D. J. Am. Chem. Soc. 1956, 78, 4765. (2) (a) Shen, Y.; Chen, C. F. Chem. Rev. 2012, 112, 1463; (b) Gingras, M. Chem. Soc. Rev. 2013, 42, 968; (c) Gingras, M.; Felix, G.; Peresutti, R. Chem. Soc. Rev. 2013, 42, 1007; (d) Gingras, M. Chem. Soc. Rev. 2013, 42, 1051; (e) Chen, C.-F.; Shen, C.-Y. Helicene Chemistry, From Synthesis to Applications; Springer, Berlin, 2017. (3) Mori, K.; Murase, T.; Fujita, M. Angew. Chem. Int. Ed. 2015, 54, 6847. (4) Nejedlý, J.; Šámal, M.; Rybáček, J.; Tobrmanová, M.; Szydlo, F.; Coudret, C.; Neumeier, M.; Vacek, J.; Vacek Chocholoušová, J.; Buděšínský, M.; Šaman, D.; Bednárová, L.; Sieger, L.; Stará, I. G.; Starý, I. Angew. Chem. Int. Ed. 2017, 56, 5839. (5) For recent double helicenes, see: (a) Fujikawa, T.; Segawa, Y.; Itami, K. J. Am. Chem. Soc. 2015, 137, 7763; (b) Sakamaki, D.; Kumano, D.; Yashima, E.; Seki, S. Angew. Chem. Int. Ed. 2015, 54, 5404; (c) Katayama, T.; Nakatsuka, S.; Hirai, H.; Yasuda, N.; Kumar, J.; Kawai, T.; Hatakeyama, T. J. Am. Chem. Soc. 2016, 138, 5210; (d) Wang, X. Y.; Narita, A.; Zhang, W.; Feng, X.; Müllen, K. J. Am. Chem. Soc. 2016, 138, 9021; (e) Wang, X. Y.; Wang, X. C.; Narita, A.; Wagner, M.; Cao, X. Y.; Feng, X.; Müllen, K. J. Am. Chem. Soc. 2016, 138, 12783; (f) Ferreira, M.; Naulet, G.; Gallardo, H.; Dechambenoit, P.; Bock, H.; Durola, F. Angew. Chem. Int. Ed. 2017, 56, 3379; (g) Hu, Y.; Wang, X. Y.; Peng, P. X.; Wang, X. C.; Cao, X. Y.; Feng, X.; Müllen, K. Narita, A. Angew. Chem. Int. Ed. 2017, 56, 3374. (6) For recent triple helicenes, see: (a) Pradhan, A.; Dechambenoit, P.; Bock, H.; Durola, F. Angew. Chem. Int. Ed. 2011, 50, 12582; (b) Yanney,
M.; Fronczek, F. R.; Henry, W. P.; Beard, D. J.; Sygula, A. Eur. J. Org. Chem. 2011, 2011, 6636; (c) Pradhan, A.; Dechambenoit, P.; Bock, H.; Durola, F. J. Org. Chem. 2013, 78, 2266; (d) Meng, D.; Fu, H.; Xiao, C.; Meng, X.; Winands, T.; Ma, W.; Wei, W.; Fan, B.; Huo, L.; Doltsinis, N. L.; Li, Y.; Sun, Y.; Wang, Z. J. Am. Chem. Soc. 2016, 138, 10184; (e) Saito, H.; Uchida, A.; Watanabe, S. J. Org. Chem. 2017, 82, 5663. (7) For quadruple helicene, see: Fujikawa, T.; Segawa, Y.; Itami, K. J. Am. Chem. Soc. 2016, 138, 3587. (8) For quintuple helicene, see: Kato, K.; Segawa, Y.; Scott, L. T.; Itami, K. Angew. Chem. Int. Ed. 2018, 57, 1337. (9) For hexapole helicenes, see: (a) Xiao, S.; Myers, M.; Miao, Q.; Sanaur, S.; Pang, K.; Steigerwald, M. L.; Nuckolls, C. Angew. Chem. Int. Ed. 2005, 44, 7390; (b) Yang, Y.; Yuan, L.; Shan, B.; Liu, Z.; Miao, Q. Chem. Eur. J. 2016, 22, 18620; (c) Chen, Y.; Marszalek, T.; Fritz, T.; Baumgarten, M.; Wagner, M.; Pisula, W.; Chen, L.; Müllen, K. Chem. Commun. 2017, 53, 8474; (d) Berezhnaia, V.; Roy, M.; Vanthuyne, N.; Villa, M.; Naubron, J. V.; Rodriguez, J.; Coquerel, Y.; Gingras, M. J. Am. Chem. Soc. 2017, 139, 18508; (e) Hosokawa, T.; Takahashi, Y.; Matsushima, T.; Watanabe, S.; Kikkawa, S.; Azumaya, I.; Tsurusaki, A.; Kamikawa, K. J. Am. Chem. Soc. 2017, 139, 18512. (10) (a) Chen, L.; Hernandez, Y.; Feng, X.; Müllen, K. Angew. Chem. Int. Ed. 2012, 51, 7640; (b) Kawasumi, K.; Zhang, Q.; Segawa, Y.; Scott, L. T.; Itami, K. Nat. Chem. 2013, 5, 739; (c) Narita, A.; Wang, X. Y.; Feng, X.; Müllen, K. Chem. Soc. Rev. 2015, 44, 6616; (d) Ball, M.; Zhong, Y.; Wu, Y.; Schenck, C.; Ng, F.; Steigerwald, M.; Xiao, S.; Nuckolls, C. Acc. Chem. Res. 2015, 48, 267; (e) Segawa,Y.; Ito, H.; Itami, K. Nat. Rev. Mater. 2016, 1, 15002. (11) For helically coiled graphene nanoribbon, see: (a) Daigle, M.; Miao, D.; Lucotti, A.; Tommasini, M.; Morin, J. F. Angew. Chem. Int. Ed. 2017, 56, 6213; (b) Chalifoux, W. A. Angew. Chem. Int. Ed. 2017, 56, 8048; (c) Evans, P. J.; Ouyang, J.; Favereau, L.; Crassous, J.; Fernández, I.; Perles Hernáez, J.; Martin, N. Angew. Chem. Int. Ed. 2018, doi:10.1002/anie.201800798. (12) (a) Ettl, R.; Chao, I.; Diederich, F.; Whetten, R. L. Nature 1991, 353, 149; (b) Hawkins, J. M.; Meyer, A. Science 1993, 260, 1918; (c) Maroto, E. E.; Izquierdo, M.; Reboredo, S.; Marco-Martinez, J.; Filippone, S.; Martin, N. Acc. Chem. Res. 2014, 47, 2660. (13) Suzuki, N.; Wang, Y.; Elvati, P.; Qu, Z. B.; Kim, K.; Jiang, S.; Baumeister, E.; Lee, J.; Yeom, B.; Bahng, J. H.; Lee, J.; Violi, A.; Kotov, N. A. ACS Nano 2016, 10, 1744. (14) Peng, X.; Komatsu, N.; Bhattacharya, S.; Shimawaki, T.; Aonuma, S.; Kimura, T.; Osuka, A. Nat. Nanotechnol. 2007, 2, 361. (15) The polyphenylene precursor is a derivative of janusarene molecular host, see: Li, T.; Fan, L.; Gong, H.; Xia, Z.; Zhu, Y.; Jiang, N.; Jiang, L.; Liu, G.; Li, Y.; Wang, J. Angew. Chem. Int. Ed. 2017, 56, 9473. (16) Co2(CO)8 is an efficient catalyst for the preparation of different HPB derivatives, see: (a) Pepermans, H.; Willem, R.; Gielen, M.; Hoogzand, C. Bull. Soc. Chim. Belg. 1988, 97, 115; (b) Stabel, A.; Herwig, P.; Müllen, K.; Rabe, J. P. Angew. Chem. Int. Ed. 1995, 34, 1609. (17) Kosaka, T.; Inoue, Y.; Mori, T. J. Phys. Chem. Lett. 2016, 7, 783. (18) (a) Mercado, B. Q.; Jiang, A.; Yang, H.; Wang, Z.; Jin, H.; Liu, Z.; Olmstead, M. M.; Balch, A. L. Angew. Chem. Int. Ed. 2009, 48, 9114; (b) Tan, Y. Z.; Yang, B.; Parvez, K.; Narita, A.; Osella, S.; Beljonne, D.; Feng, X.; Müllen, K.; Nat. Commun. 2013, 4, 2646; (c) Cai, W.; Li, F. F.; Bao, L.; Xie, Y.; Lu, X. J. Am. Chem. Soc. 2016, 138, 6670; (d) Cheung, K. Y.; Chan, C. K.; Liu, Z.; Miao, Q.; Angew. Chem. Int. Ed. 2017, 56, 9003; (e) Pun, S. H.; Chan, C. K.; Luo, J.; Liu, Z.; Miao, Q. Angew. Chem. Int. Ed. 2018, 57, 1581. (19) Krygowski, T. M.; Cyrański, M. K. Chem. Rev. 2001, 101, 1385. (20) Randić, M. Chem. Rev. 2003, 103, 3449. (21) Fasel, R.; Parschau, M.; Ernst, K. H. Nature 2006, 439, 449. (22) Martin, R. H.; Marchant, M. J. Tetrahedron 1974, 30, 347. (23) Herwig, P. T.; Enkelmann, V.; Schmelz, O.; Müllen, K. Chem. Eur. J. 2000, 6, 1834. (24) Intramolecular π-to-π contact between the neighboring DBP blades (~3.0 Å) is observed in the crystal structure of H7H2, which suggests a through-space electron delocalization. See: (a) Liberko, C. A.; Miller, L. L.; Katz, T. J.; Liu, L. J. Am. Chem. Soc. 1993, 115, 2478; (b) Sargent, A. L.; Almolf, J.; Liberko, C. A. J. Phys. Chem. 1994, 98, 6114; (c) Schuster, N. J.; Paley, D. W.; Jockusch, S.; Ng, F.; Steigerwald, M. L.; Nuckolls, C. Angew. Chem. Int. Ed. 2016, 55, 13519. (25) Brandt, J. R.; Salerno, F.; Fuchter, M. J. Nat. Rev. Chem. 2017, 1, 0045.
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