Regioselective Oxidation of Fused-Pentagon Chlorofullerenes

Jan 4, 2016 - Synopsis. Two representative monoxides, #271C50Cl10O and #913C56Cl10O, featured with fused pentagons, were obtained to demonstrate ...
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Regioselective Oxidation of Fused-Pentagon Chlorofullerenes Zhen-Qiang Zhang, Shu-Fen Chen, Cong-Li Gao, Ting Zhou, Gui-Juan Shan, Yuan-Zhi Tan,* Su-Yuan Xie,* Rong-Bin Huang, and Lan-Sun Zheng Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory for Physical Chemistry of Solid Surfaces, and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China S Supporting Information *

endohedral non-IPR fullerene, La@#10612C72 with one pair of fused pentagons was regioselectively added to a dichlorophenyl group at the ortho-site of its fused pentagon unit,29 and non-IPR La2@#10611C72 showed that the carbon atoms at the ortho-site of fused pentagons are easier to be attacked by the adamantylidene carbene addition.30 All of these chemical modifications of nonIPR fullerenes revealed the fused-pentagon-relevant regioselectivity. In the aspect of fullerene oxidation, compared with the flourish of IPR fullerene oxides, the oxidation of non-IPR fullerenes was merely predicted by theoretical investigations heretofore.31−33 Here, we show two representative non-IPR chlorofullerene oxides, i.e., #271C50Cl10O and #913C56Cl10O. Both oxides have an epoxy structure on the cage located at the orthosite of the double-fused-pentagon unit, which was clearly determined by crystallography. Detailed structural comparison reveals that the oxidation in both #271C50Cl10O and #913C56Cl10O prefers to occur at the localized olefinic bond of their corresponding chlorofullerenes. Both monoxides, #271C50Cl10O and #913C56Cl10O, are obtained by slow oxidation of purified #271C50Cl10 and #913C56Cl10 under ambient conditions by the oxygen in the air (Figure 1). In Figure 1a and b, it clearly shows an additional peak emerged in HPLC after three months of slow oxidation under ambient conditions, which was identified as #271C50Cl10O and #913C56Cl10O in terms of mass spectra (Figure 1c,d), respectively. The yield of oxidation is relatively low (less than 5%), but both #271C50Cl10O and #913 C56Cl10O are the only isolatable product of the oxidation, showing good selectivity (Figure 1a,b). We proposed that the subsequent oxidation of #271C50Cl10 and #913C56Cl10 in carbonaceous soot during the storage and separation process would also lead the formation of both monoxides, which is similar to the case of oxidation of Ih-C60.8,9 Successfully, both #271C50Cl10O and #913 C56Cl10O were also isolated by multistage HPLC separations from the carbonaceous soot extraction (SI S1 and S2). Furthermore, we carried out the intentional chemical oxidation of #271C50Cl10O and #271C50Cl10O using O2 as oxidant. However, we found that the epoxidation of #271C50Cl10O and #913C56Cl10O did not occur either by photo-oxygenation or by thermal oxygenation for relatively short reaction time (shorter than 2 days) (SI S3), suggesting that the epoxidation of #271C50Cl10O and #913C56Cl10O was kinetically very slow, similar to the epoxidation of C60(CF3)10.34 We performed the multistage mass spectra (MSn) characterization of #271C50Cl10O and #913C56Cl10O (Figure 1c,d), where

ABSTRACT: Two monoxides of typical smaller chlorofullerenes, #271C50Cl10O and #913C56Cl10O, featured with double-fused-pentagons, were synthesized to demonstrate further regioselective functionalization of non-IPR (IPR = isolated pentagon rule) chlorofullerenes. Both non-IPR chlorofullerene oxides exhibit an epoxy structure at the ortho-site of fused pentagons. In terms of the geometrical analysis and theoretical calculations, the principles for regioselective epoxy oxidation of non-IPR chlorofullerenes are revealed to follow both “fused-pentagon ortho-site” and “olefinic bond” rules, which are valuable for prediction of oxidation of non-IPR chlorofullerenes. xidation is crucial for π-conjugated nanocarbons,1−3 such as fullerenes and carbon nanotubes, as well as graphenes, because oxygenous groups introduced by oxidation not only modulate the inherent chemical and physical properties of nanocarbons, but also provide a versatile platform for the further functionalization.4−6 In the field of fullerenes, since the macroscopic synthesis of fullerenes,7 many efforts have been devoted to the synthesis of fullerene oxides by a range of methods, including arc-discharge, combustion, organic synthesis, etc.6,8−11 In 1991, the first fullerene monoxide, C70O, was isolated from fullerene soot by Diederich et al.,8 and then, C60O was synthesized by Creegan et al.9 On the other hand, fullerene oxides exhibit rich chemical properties and are easy to be converted into other fullerene derivatives, such as fulleroid alcohols, aldehydes, and ethers,6,11−13 which are potentially useful in electronics, biomaterials, and others.11,14 To date, a growing number of various fullerene oxides, e.g., C60On (1 ≤ n ≤ 13),10,15−17 C60FxOy (x all even and x ≤ 18, x + 2y ≤ 58),18−20 C60F17O·OH,21 C60Me5O2OH,22 C60(O)n(OOtBu)4 (n = 1, 2),23,24 and C70O,25,26 have come into reality. However, the studies of fullerene oxides were still limited to the IPR (IPR = Isolated Pentagon Rule) fullerenes such as Ih-C60 and D5h-C70 so far, simply owing to their feasible availability. By contrast, fullerenes with fused-pentagons, so-called nonIPR fullerenes, are scarce due to their instable nature. In the past decade, non-IPR fullerenes, which can be obtained in terms of exohedral or endohedral stabilization, have shown their unique reactivity subjecting to further chemical modification. For example, non-IPR #1809C60Cl8 can be selectively converted into #1809 C60Cl4(C6H5)4 through a Friedel−Crafts reaction.27 The higher non-IPR fullerene, #23863C78Cl8, also exhibited a regioselective nucleophilic substitution.28 For the cases of

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© XXXX American Chemical Society

Received: September 30, 2015

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DOI: 10.1021/acs.inorgchem.5b02239 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

Figure 2. ORTEP structures and Schlegel diagrams of the chlorofullerene monoxides. (a, b) #271C50Cl10O; (c, d) #913C56Cl10O. The thermal ellipsoids are drawn at 50% probability level. The fusedpentagon units are highlighted in cyan. The exohedral chlorine atoms and oxygen atom are represented as green and red dots in the Schlegel diagrams. Four types of carbon in #271C50 cage are labeled with a Roman numeral. The C16 fragment in #913C56Cl10O is indicated by orange dash line.

Figure 1. HPLC of purified (black) and oxidized (red) #271C50Cl10 (a), HPLC of purified (black) and oxidized (red) #913C56Cl10 (b), and respective multistage mass spectra of #271C50Cl10O and #913C56Cl10O (c, d). Inserts show the experimental and simulated mass spectra of #271 C50Cl10O and #913C56Cl10O.

the #271C50Cl10O or #913C56Cl10O molecules collide with highenergy helium in an ion trap. Of interest, the MSn of #271C50Cl10O and #913C56Cl10O (Figure 1c,d) show a stepwise detachment of chlorine instead of oxygen (Figure 1c,d), which would be attributed to the stronger C−O bond and smaller collision cross section of the oxygen atom compared with chlorine. The difficulty of detachment of oxygen in #271C50Cl10O and #913 C56Cl10O is similar to the case of epoxide C60O, suggesting these two monoxides #271C50Cl10O and #913C56Cl10O would also have an epoxy structure. The detailed structures of #271C50Cl10O and #913C56Cl10O were disclosed by single crystal X-ray diffraction (SI S4). Shown in Figure 2a,b is the structure of #271C50Cl10O depicted in ORTEP and Schlegel format. #271C50 stabilized as #271C50Cl10 is the first small fullerene synthesized macroscopically. 35 #271 C50Cl10O here presents the first experimental example of the derivatization of #271C50Cl10. The most distinguished characteristic of #271C50Cl10O is the oxygen at the ortho-position of the fused-pentagon unit (Figure 2a,b) in comparison with the parental #271C50Cl10. The oxidation structure of #271C50Cl10O is an epoxy group, the same as the oxidation of Ih-C60 or D5h-C70, whereas the previously reported oxidation of halogenated fullerenes (C60F18) produced the intramolecular ester.19 Compared with the regioselective addition reaction of non-IPR endofullerenes La@#10612C7229 and La2@#10611C72,30 the oxidation addition of #271C50Cl10 also located at the ortho-position of fused pentagons, hinting that the ortho-positions of fused pentagons are more ready to be attacked during chemical modification, which was further corroborated by the oxidation of #913 C56Cl10 (vide inf ra). The oxidation of olefin in principle occurs at the double bond to afford epoxy products, which was verified in the cases of previously reported epoxidation of C60 derivatives.22,34,36 Similarly, the oxidation of #271C50Cl10 to epoxide #271C50Cl10O should occur at the bond with most double-bond character.22,34,36 Indeed, the oxidation site of #271C50Cl10O is exactly at the shortest bond (CIII−CIII, 1.380 Å, Table S2) in #271C50Cl10.

On the formation of epoxide, the bond length of CIII-CIII with the epoxy group was elongated to 1.511 Å. By DFT calculations (SI S6), as shown in Figure S5, we found that the shortest CIII−CIII bond had the highest HOMO occupancy rate, indicating that the CIII−CIII bond is most feasible to the oxidation, consistent with the structural analysis. C56 is the most abundant small fullerene, and three isomers of C56 (#864, 913, and 916)37−39 have already been captured and characterized. Among them, #913C56, captured as #913C56Cl10, was the first isomer reported.37 Under similar conditions with #271 C50Cl10, #913C56Cl10 can be oxidized to produce the sole product #913C56Cl10O (Figure 1b). As revealed by crystallography (Figure 2c,d), #913C56Cl10O has an epoxy structure at the orthoposition of the fused pentagons, the same as the case of #271 C50Cl10O and in agreement well with our proposal that regioselective oxidation of non-IPR chlorofullerenes prefers to occur at the ortho-position of fused pentagons. In #913C56Cl10, there are four kinds of C−C bonds (Figure 2d and Table S3) at the ortho-position of fused pentagons, three of which exhibit a typical olefinic character with bond length from 1.349 to 1.362 Å (Table S3). The oxidation of #913C56Cl10 would take place at these olefinic bonds. Indeed, the epoxy group in #913C56Cl10O was added at the shortest olefinic bond of the C16 fragment (Figure 2d). We further calculated the HOMO structure of #913C56Cl10 by DFT computation (SI S6), which is responsible to the oxidation reactivity. The HOMO structure of #913C56Cl10 clearly shows that the olefinic bond at the C16 fragment, where the epoxidation occurs, possesses the highest HOMO occupancy rate (Figure S6), consistent with the geometrical analysis. Therefore, supported by the structures of #271C50Cl10O and #913C56Cl10O, we found the epoxy oxidation tended to occur at the short olefinic bonds at the ortho-position of fused pentagon unit, which can be a general rule to predict the regioselective oxidation of non-IPR chlorofullerenes. B

DOI: 10.1021/acs.inorgchem.5b02239 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

(15) Heymann, D.; Bachilo, S. M.; Weisman, R. B.; Cataldo, F.; Fokkens, R. H.; Nibbering, N. M. M.; Vis, R. D.; Chibante, L. P. F. J. Am. Chem. Soc. 2000, 122, 11473. (16) Weisman, R. B.; Heymann, D.; Bachilo, S. M. J. Am. Chem. Soc. 2001, 123, 9720. (17) Taliani, C.; Ruani, G.; Zamboni, R.; Danieli, R.; Rossini, S.; Denisov, V. N.; Burlakov, V. M.; Negri, F.; Orlandi, G.; Zerbetto, F. J. Chem. Soc., Chem. Commun. 1993, 3, 220. (18) Taylor, R.; Langley, G. J.; Brisdon, A. K.; Holloway, J. H.; Hope, E. G.; Kroto, H. W.; Walton, D. R. M. J. Chem. Soc., Chem. Commun. 1993, 3, 875. (19) Boltalina, O. V.; Troshin, P. A.; de La Vaissiere, B.; Fowler, P. W.; Sandall, J. P. B.; Hitchcock, P. B.; Taylor, R. Chem. Commun. 2000, 14, 1325. (20) Boltalina, O. V.; Lukonin, A. Y.; Avent, A. G.; Street, J. M.; Taylor, R. J. Chem. Soc., Perkin Trans. 2000, 2, 683. (21) Darwish, A. D.; Abdul-Sada, A. a. K.; Avent, A. G.; Street, J. M.; Taylor, R. J. Fluorine Chem. 2003, 121, 185. (22) Al-Matar, H.; Hitchcock, P. B.; Avent, A. G.; Taylor, R. Chem. Commun. 2000, 14, 1071. (23) Yao, J. Y.; Yang, D. Z.; Xiao, Z.; Gan, L. B.; Wang, Z. M. J. Org. Chem. 2009, 74, 3528. (24) Huang, S. H.; Xiao, Z.; Wang, F. D.; Zhou, J.; Yuan, G.; Zhang, S. W.; Chen, Z. F.; Thiel, W.; Schleyer, P. v. R.; Zhang, X.; Hu, X. Q.; Chen, B. C.; Gan, L. B. Chem. - Eur. J. 2005, 11, 5449. (25) Smith, A. B.; Strongin, R. M.; Brard, L.; Furst, G. T.; Atkins, J. H.; Romanow, W. J.; Saunders, M.; Jiménez-Vázquez, H. A.; Owens, K. G.; Goldschmidt, R. J. J. Org. Chem. 1996, 61, 1904. (26) Heymann, D.; Bachilo, S. M.; Weisman, R. B. J. Am. Chem. Soc. 2002, 124, 6317. (27) Tan, Y. Z. L.; Liao, Z.-J.; Qian, Z. Z.; Chen, R. T.; Wu, X.; Liang, H.; Han, X.; Zhu, F.; Zhou, S. J.; Zheng, Z. P.; Lu, X.; Xie, S. Y.; Huang, R. B.; Zheng, L. S. Nat. Mater. 2008, 7, 790. (28) Tan, Y. Z.; Li, J.; Zhou, T.; Feng, Y. Q.; Lin, S. C.; Lu, X.; Zhan, Z. P.; Xie, S. Y.; Huang, R. B.; Zheng, L. S. J. Am. Chem. Soc. 2010, 132, 12648. (29) Wakahara, T.; Nikawa, H.; Kikuchi, T.; Nakahodo, T.; Rahman, G. M. A.; Tsuchiya, T.; Maeda, Y.; Akasaka, T.; Yoza, K.; Horn, E.; Yamamoto, K.; Mizorogi, N.; Slanina, Z.; Nagase, S. J. Am. Chem. Soc. 2006, 128, 14228. (30) Lu, X.; Nikawa, H.; Tsuchiya, T.; Maeda, Y.; Ishitsuka, M. O.; Akasaka, T.; Toki, M.; Sawa, H.; Slanina, Z.; Mizorogi, N.; Nagase, S. Angew. Chem., Int. Ed. 2008, 47, 8642. (31) Xu, X. F.; Shang, Z. F.; Wang, G. C.; Cai, Z. S.; Pan, Y. M.; Zhao, X. Z. J. Mol. Struct.: THEOCHEM 2002, 589-590, 265. (32) Liang, C.; Yang, J.; Hao, C.; Li, S. M.; Li, Y.; Jin, Y. F. J. Mol. Struct.: THEOCHEM 2008, 851, 342. (33) Xu, X. F.; Xing, Y. M.; Yang, X.; Wang, G. C.; Cai, Z. S.; Shang, Z. F.; Pan, Y. M.; Zhao, X. Z. Int. J. Quantum Chem. 2005, 101, 160. (34) Whitaker, J. B.; Shustova, N. B.; Strauss, S. H.; Boltalina, O. V. Acta Chim. Slov. 2013, 60, 577. (35) Xie, S. Y.; Gao, F.; Lu, X.; Huang, R. B.; Wang, C. R.; Zhang, X.; Liu, M. L.; Deng, S. L.; Zheng, L. S. Science 2004, 304, 699. (36) Kareev, I. E.; Shustova, N. B.; Kuvychko, I. V.; Lebedkin, S. F.; Miller, S. M.; Anderson, O. P.; Popov, A. A.; Strauss, S. H.; Boltalina, O. V. J. Am. Chem. Soc. 2006, 128, 12268. (37) Tan, Y. Z.; Han, X.; Wu, X.; Meng, Y. Y.; Zhu, F.; Qian, Z. Z.; Liao, Z. J.; Chen, M. H.; Lu, X.; Xie, S. Y.; Huang, R. B.; Zheng, L. S. J. Am. Chem. Soc. 2008, 130, 15240. (38) Tan, Y. Z.; Li, J.; Zhu, F.; Han, X.; Jiang, W. S.; Huang, R. B.; Zheng, Z.; Qian, Z. Z.; Chen, R. T.; Liao, Z. J.; Xie, S. Y.; Lu, X.; Zheng, L. S. Nat. Chem. 2010, 2, 269. (39) Zhou, T.; Tan, Y. Z.; Shan, G. J.; Zou, X. M.; Gao, C. L.; Li, X.; Li, K.; Deng, L. L.; Huang, R. B.; Zheng, L. S.; Xie, S. Y. Chem. - Eur. J. 2011, 17, 8529.

In summary, the oxidation of two typical non-IPR chlorofullerenes, #271C50Cl10 and #913C56Cl10, affords the regioselective monoxides #271C50Cl10O and #913C56Cl10O, which present the first case of non-IPR fullerene oxides. By structural analysis and DFT calculations, we proposed the “olefinic bond” and “fused-pentagon ortho-site” rules to account for the regioselective oxidation of these two non-IPR chlorofullerenes, which will be a guideline for the oxidation of non-IPR chlorofullerenes.

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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.inorgchem.5b02239. HPLC isolation of #271C50Cl10O and #913C56Cl10O, mass spectra, detailed geometrical parameter and computation details. (PDF) Crystallographic information. (CIF) Crystallographic information. (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.-Z.T.). *E-mail: [email protected] (S.-Y.X.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the 973 Project (2014CB845601) and National Science Foundation of China (U1205111, 21390390, 21401156, 51572231).

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REFERENCES

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DOI: 10.1021/acs.inorgchem.5b02239 Inorg. Chem. XXXX, XXX, XXX−XXX