DOI: 10.1002/asia.201500521
Communication
Fullerenes
Capturing C90 Isomers as CF3 Derivatives: C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18 Nadezhda B. Tamm and Sergey I. Troyanov*[a] Abstract: High-temperature trifluoromethylation of a C90 isomeric mixture with CF3I followed by HPLC separation of C90(CF3)n isomers resulted in the isolation of several individual C90(CF3)14¢18 compounds. Single crystal X-ray diffraction with the use of synchrotron radiation resulted in the structure determination of C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18. Their addition patterns are discussed and compared with the known isomers C90(30)(CF3)18 and C90(35)(CF3)14, respectively. The presence of the most stable C90 isomer, C90(45), in the fullerene soot has been confirmed for the first time.
The investigation of the chemistry of higher fullerenes and even their identification is hampered by the low abundance in the fullerene soot, by the existence of numerous cage isomers, and the difficulties of their separation. The classical identification method by 13C NMR spectroscopy fails for higher fullerenes above C90.[1] Direct X-ray diffraction methods are useful, if the cage mobility (rotation or libration) is restrained by cocrystallization, for example, with metal porphyrinates.[2] Derivatization of higher fullerenes followed by separation of derivatives and their structural investigation proved its efficiency not only for identification but also for investigation of higher fullerene reactivity in cases of C76–C90,[3a,b] C94,[3c] C96,[3d] and C100.[3e] Because of elaborated synthesis and separation methods, most investigated are chlorido and perfluoroalkyl derivatives of higher fullerenes. C90 fullerene has 46 topologically possible IPR (isolated pentagon rule)-obeying isomers.[4] In an early 13C NMR spectroscopic study of a C90 fraction, the presence of at least five C90 isomers with C1 (one), C2 (three), and C2v (one) symmetry was suggested, however, without any further assignment.[5] X-ray diffraction studies allowed unambiguous identification of isomers D5h-C90(1), C1-C90(30), and C1-C90(32) (isomer numbers in parentheses according to the spiral algorithm[4]) as co-crystals with NiII(OEP) (OEP = octaethylporphyrin).[6a,b] The cage connec-
[a] Dr. N. B. Tamm, Prof. Dr. S. I. Troyanov Chemistry Department Moscow State University Leninskie gory, 119991, Moscow (Russia) E-mail: [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201500521. Chem. Asian J. 2015, 10, 1622 – 1625
tivity of D5h-C90(1) was also confirmed by a single-crystal X-ray study of a solvate with CS2.[6c] A trifluoromethylated derivative of C90, C90(CF3)12, was suggested to contain a C1-C90(32) cage on the basis of its 19F NMR spectrum.[3a] Recently, two other CF3 derivatives, C90(30)(CF3)18 and C90(35)(CF3)14, have been isolated and crystallographically characterized.[7] Single-crystal X-ray investigations of C90 chlorides, C90Cl22¢32, evidenced the presence of six C90 isomers, C2C90(28), C1-C90(30), C1-C90(32), Cs-C90(34), Cs-C90(35), and C2vC90(46), in the fullerene soot.[8] It was found that high-temperature chlorination of C2-C90(28) can proceed under cage shrinkage via a C2 loss and formation of chlorides with a non-classical (NC) cage, C88(NC)Cl22/24.[9] Several theoretical calculations have been performed to establish the relative stability of C90 isomers and estimate their relative populations in the experimental mixtures.[10] According to ref. [10a], the stability of C90 isomers in the ground state decreases in the order: 45, 46, 35, 18, and 9. Based on both thermodynamic and kinetic stabilities computed at the B3LYP/631G level, a somewhat different order of stability, 45, 46, 35, 30, 28, 40, 32, was concluded.[10b] Later on, a different stability sequence, 45 > 46 1 35 > 30 32 > 28 > 29 31 > 27 34, was obtained by using the PM3 method.[10c] It is noteworthy that most of the theoretically predicted isomers have been experimentally confirmed except the most stable C2-C90(45). The present communication further contributes to the chemistry of C90 isomers. Trifluoromethylation of a mixture of C90 isomers followed by HPLC separation and X-ray diffraction study allowed structural characterization of C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18. Significantly, while other CF3 and chlorido derivatives of C90(30) and C90(35) were known from previous studies, isomer C90(45) has been captured for the first time, thus evidencing the presence of the most stable C90 isomer in the fullerene soot. Trifluoromethylation of a C90 HPLC fraction with gaseous CF3I was carried out in a quartz ampoule at 450 8C for 1.5 h following a procedure described previously.[11] The product containing C90(CF3)14-18 was dissolved in n-hexane and subjected to HPLC separation using a Buckyprep column (10 Õ 250 mm, Nacalai Tesque Inc.) and n-hexane as the eluent at a flow rate of 4.6 mL min¢1. A total of 5 of the 32 fractions, with retention times of 4–85 min (see the Supporting Information for more details), gave small crystals upon recrystallization from toluene or p-xylene. An X-ray diffraction study with the use of synchrotron radiation revealed the structures of C90(30)(CF3)14,
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Communication C90(35)(CF3)16/18, C90(45)(CF3)16, and C90(45)(CF3)18, the latter containing an admixture of C90(46)(CF3)18.[12] Three of five structurally characterized C90(CF3)n molecules, C1-C90(30)(CF3)14, C1-C90(35)(CF3)16, and C1-C90(45)(CF3)16, are shown in Figure 1. While the carbon cage of C1-C90(30) is asymmetric, the cages of Cs-C90(35) and C2-C90(45) possess mirror
Figure 3. Schlegel diagrams of C1-C90(35)(CF3)16 and Cs-C90(35)(CF3)18. Cage pentagons are highlighted with gray. Black triangles denote the positions of the attached CF3 groups. Isolated benzenoid rings and isolated C=C bonds are also indicated. The Schlegel diagram of the known C1-C90(35)(CF3)14[7] corresponds to that of C1-C90(35)(CF3)16 after removal of two CF3 groups encircled by a small oval.
Figure 1. Views of the C1-C90(30)(CF3)14, C1-C90(35)(CF3)16, and C1-C90(45)(CF3)16 molecules; the latter two are presented parallel to the mirror plane and the C2 axis of the corresponding carbon cages, respectively.
and C2 axial symmetry, respectively. Symmetry lowering of the whole C90(CF3)16 molecules results from asymmetric additions of CF3 groups. The addition of two CF3 groups in CsC90(35)(CF3)18 restores mirror symmetry, whereas the C1C90(45)(CF3)18 molecule remains asymmetric. Schlegel diagrams of C1-C90(30)(CF3)14 and the known C1C90(30)(CF3)18 molecule[7] are shown in Figure 2. The addition
Figure 2. Schlegel diagrams of C1-C90(30)(CF3)14 and the known C1C90(30)(CF3)18.[7] Cage pentagons are highlighted with gray. Black triangles denote the positions of the attached CF3 groups. Nearly isolated benzenoid rings and isolated C=C bonds are also indicated.
patterns of both molecules contain 12 common positions of CF3 attachment so that the former is nearly a substructure of the latter. All CF3 groups in the C1-C90(30)(CF3)14 molecule are attached in para positions in C6(CF3)2 hexagons. Its addition pattern contains a nearly isolated benzenoid ring and one isolated C=C bond, whereas there are three isolated C=C bonds in the C1-C90(30)(CF3)18 molecule. Schlegel diagrams of the C1-C90(35)(CF3)16 and CsC90(35)(CF3)18 molecules are presented in Figure 3. The addition pattern of C1-C90(35)(CF3)16 contains two isolated C=C bonds and two benzenoid rings, one of which (the outer hexagon) is nearly isolated. The mirror symmetrical addition pattern of the Cs-C90(35)(CF3)18 molecule has two benzenoid rings and three Chem. Asian J. 2015, 10, 1622 – 1625
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isolated C=C bonds. The addition pattern of the known C1C90(35)(CF3)14[7] can be produced from that of C1-C90(35)(CF3)16 by the removal of two CF3 groups which are indicated in Figure 3. Therefore, three C90(35)(CF3)14/16/18 molecules are related with each other by simple addition (removal) of two CF3 groups which allows the suggestion that the lower derivatives are precursors of the higher ones in the course of trifluoromethylation. Similar relations have been reported for the experimentally isolated isomers of C84(22)(CF3)12/14/16,[11a] C84(23)(CF3)10/12,14/16,[11b] and C88(33)(CF3)16/18/20.[11c] Figure 4 shows Schlegel diagrams of the C1-C90(45)(CF3)16 and C1-C90(45)(CF3)18 molecules which are the first experimental evidence of the presence of isomer C2-C90(45) in the fullerene
Figure 4. Schlegel diagrams of C1-C90(45)(CF3)16 and C1-C90(45)(CF3)18. Cage pentagons are highlighted with gray. Black triangles denote the positions of the attached CF3 groups. Isolated benzenoid rings and isolated C=C bonds are also indicated. Dashed lines on the Schlegel diagram of C1-C90(45)(CF3)18 indicate the alternative position of the isolated C=C bond due to the presence of C1-C90(46)(CF3)18 in the same crystallographic site.
soot. The addition pattern of C1-C90(45)(CF3)16 is characterized by the presence of two benzeniod rings (one is partially isolated) and two isolated C=C bonds, whereas the C1-C90(45)(CF3)18 molecule contains three benzenoid rings (two are partially isolated) and three isolated C=C bonds. The attachment positions of 14 CF3 groups are common in both molecules. In C1C90(45)(CF3)18, the average C¢C bond length of benzenoid rings is 1.397 æ; the average length of C=C bonds is 1.32 æ. The structure determination of C1-C90(45)(CF3)18 revealed that one of the isolated C=C bonds is disordered between two positions related by a rotation by approximately 908 which re-
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Communication sembles a Stone–Wales rearrangement (SWR) in the carbon cage (dashed lines on the Schlegel diagram). In fact, the disorder of a C=C bond indicates the presence of a C90(46)(CF3)18 molecule in the same crystallographic site (with ca. 30 % occupancy). While the carbon cages of C2-C90(45) and C2v-C90(46) are connected by one SWR, the addition patterns of all 18 CF3 groups are exactly the same. Thus, similar shapes of both molecules are responsible for identical (or very close) retention times during HPLC separation and for their capability for mutual substitution in the crystal packing. Similar co-crystallization phenomena of the derivatives of higher fullerenes with the same addition patterns but different cage isomers have been also found in the crystal structures of C78(2,3)Br18,[13a] C84(11,14,16)Cl22,[13b] C90(34,46)Cl32,[13c] and C104(811,812)Cl24.[13d] A comparison of the molecular structures of C90(CF3)14¢18 with carbon cages of C90(30), C90(35), and C90(45) demonstrates some common features of their addition patterns. Most of additions of CF3 groups occur in para positions with the formation of chains of adjacent C6(CF3)2 hexagons. The length of the chains is limited because further addition in a para position would require an attachment to the carbon atoms in THJs (triple hexagon junctions), which is energetically unfavorable. The stabilizing factor is the formation of one, two or three isolated C=C bonds in the molecules with 14, 16, or 18 attached CF3 groups, respectively. Further stabilization occurs due to formation of aromatic substructures, isolated or nearly isolated benzenoid rings, on the carbon cages. The addition patterns of the C90(CF3)14,16,18 molecules exhibit similar features as the most extensively studied CF3 derivatives of C84 (isomers 16, 18, 22, and 23), in which the addition to THJ has not been observed.[11] However, the addition of two CF3 groups in THJs was established in the overcrowded molecule of C94(61)(CF3)20.[14a] Several C76(1)(CF3)14¢18 molecules contain one or two CF3 groups in THJs.[14b] In the latter cases, the presence of additions in THJs can be explained by the simultaneous formation of isolated benzenoid rings or/and isolated butadiene fragments on the C76 carbon cage. An important result of the present work is the first confirmation of the presence of isomer C90(45) in the fullerene soot, which was highly expected to be isolated experimentally as the most stable isomer of C90 according to quantum chemical calculations by different methods.[10] Now the set of seven experimentally confirmed isomers of C90 includes all isomers of high (nos. 45, 46, 1) or middle relative stability (nos. 35, 30, 32, 28).[10c] Interestingly, carbon cages of these isomers (except D5hC90(1)) are interconnected by only one or two SWRs of the pyracylene type.[1, 8] In particular, two-step pathways between isomers C90(30), C90(35), and C90(45) include isomer C1-C90(32) as an intermediate cage. Isomer C90(46) can be transformed into C90(35) or C90(45) by only one SWR, the latter pathway having been discussed above and shown in Figure 4. In summary, the high-temperature trifluoromethylation of a C90 isomeric mixture with CF3I followed by HPLC separation of C90(CF3)n isomers resulted in the isolation and structure determination of several CF3 derivatives of C90(30), C90(35), and C90(45) with 14–18 attached CF3 groups. Therefore, the structural chemistry of trifluromethylated isomers of C90 is signifiChem. Asian J. 2015, 10, 1622 – 1625
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cantly extended allowing the formulation of general rules concerning their addition patterns. More importantly, isomer C90(45) has been captured as two CF3 derivatives, thus confirming the earlier predictions about its presence in the fullerene soot based on its highest relative stability among the 46 topologically possible isomers of C90 fullerene. It is also remarkable that isomer C90(45) has been captured as a result of trifluoromethylation and HPLC separation, but not by the chlorination method, which was widely used for the first identification of numerous isomers of higher fullerenes.
Acknowledgements This work was supported by the the Russian Foundation for Basic Research (15-03-04464 and 13-03-91332). Keywords: C90 · fullerenes · HPLC · structure elucidation · trifluoromethylation [1] T. Minami, Y. Miyake, K. Kikuchi, Y. Achiba in The 18th Fullerene General Symposium, The Fullerene Research Association of Japan, Okazaki, 2001, p. 42. [2] a) Z. Wang, H. Yang, A. Jiang, Z. Liu, M. M. Olmstead, A. L. Balch, Chem. Commun. 2010, 46, 5262; b) H. Yang, H. Jin, Y. Che, B. Hong, Z. Liu, J. A. Gharamaleki, M. M. Olmstead, A. L. Balch, Chem. Eur. J. 2012, 18, 2792. [3] a) I. E. Kareev, A. A. Popov, I. V. Kuvychko, N. B. Shustova, S. F. Lebedkin, V. P. Bubnov, O. P. Anderson, K. Seppelt, S. H. Strauss, O. V. Boltalina, J. Am. Chem. Soc. 2008, 130, 13471; b) K. S. Simeonov, K. Yu. Amsharov, M. Jansen, Chem. Eur. J. 2008, 14, 9585; c) N. B. Tamm, S. Yang, T. Wei, S. I. Troyanov, Inorg. Chem. 2015, 54, 2494; d) S. Yang, T. Wei, E. Kemnitz, S. I. Troyanov, Angew. Chem. Int. Ed. 2012, 51, 8239; Angew. Chem. 2012, 124, 8364; e) M. A. Fritz, E. Kemnitz, S. I. Troyanov, Chem. Commun. 2014, 50, 14577. [4] P. W. Fowler, D. E. Manolopoulos, An Atlas of Fullerenes, Clarendon Press, Oxford, UK, 1995. [5] Y. Achiba, K. Kikuchi, Y. Aihara, T. Wakabayashi, Y. Miyake, M. Kainosho in The Chemical Physics of Fullerenes 10 (and 5) Years Later (Ed.: W. Andreoni), Kluwer, Dordrecht, 1996, p. 139. [6] a) H. Yang, C. M. Beavers, Z. Wang, A. Jiang, Z. Liu, H. Jin, B. Q. Mercado, M. M. Olmstead, A. L. Balch, Angew. Chem. Int. Ed. 2010, 49, 886; Angew. Chem. 2010, 122, 898; b) H. Yang, B. Q. Mercado, H. Jin, Z. Wang, A. Jiang, Z. Liu, C. M. Beavers, M. M. Olmstead, A. L. Balch, Chem. Commun. 2011, 47, 2068; c) F. L. Bowles, B. Q. Mercado, K. B. Ghiassi, M. M. Olmstead, H. Yang, Z. Liu, A. L. Balch, Cryst. Growth Des. 2013, 13, 4591. [7] N. B. Tamm, S. I. Troyanov, Nanosyst. Phys. Chem. Math. 2014, 5, 39. [8] S. I. Troyanov, S. Yang, C. Chen, E. Kemnitz, Chem. Eur. J. 2011, 17, 10662. [9] I. N. Ioffe, O. N. Mazaleva, L. N. Sidorov, S. Yang, T. Wei, E. Kemnitz, S. I. Troyanov, Inorg. Chem. 2013, 52, 13821. [10] a) Z. Slanina, X. Zhao, S.-L. Lee, E. O˜sawa, Scr. Mater. 2000, 43, 733; b) G. Sun, Chem. Phys. 2003, 289, 371; c) M. Watanabe, D. Ishimaru, N. Mizorogi, M. Kiuchi, J. Aihara, THEOCHEM 2005, 726, 11. [11] a) K. Chang, M. A. Fritz, N. B. Tamm, A. A. Goryunkov, L. N. Sidorov, C. Chen, S. Yang, E. Kemnitz, S. I. Troyanov, Chem. Eur. J. 2013, 19, 578; b) N. A. Romanova, M. A. Fritz, K. Chang, N. B. Tamm, A. A. Goryunkov, L. N. Sidorov, C. Chen, S. Yang, E. Kemnitz, S. I. Troyanov, Chem. Eur. J. 2013, 19, 11707; c) M. A. Lanskikh, K. Chang, N. B. Tamm, E. Kemnitz, S. I. Troyanov, Mendeleev Commun. 2012, 22, 136. [12] Synchrotron X-ray data were collected at 100 K at the BESSY storage ring (BL14.2, PFS, Berlin, Germany) using a MAR225 CCD detector; l = 0.8950 and 0.8856 æ. C90(30)(CF3)14·0.5 C6H5CH3 : triclinic, P1¯, a = 14.192(1) æ, b = 19.861(1) æ, c = 29.348(3) æ, a = 93.080(10)8, b = 91.614(10)8, g = 104.479(10)8, V = 7990.5(11) æ3, Z = 4, R1(F)/wR2(F2) = 0.195/0.448 for 13169/29035 reflections and 2736 parameters. C90(35)(CF3)16·1.86 C6H5CH3 : monoclinic, C2/c, a = 24.051(1) æ, b =
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Communication 15.568(1) æ, c = 43.921(3) æ, b = 97.034(6)8, V = 16321.4(17) æ3, Z = 8, R1(F)/wR2(F2) = 0.117/0.210 for 6189/17612 reflections and 1536 parameters. C90(35)(CF3)18·1.17 p-C6H4(CH3)2 : monoclinic, P21/c, a = 14.278(1) æ, b = 24.542(2) æ, c = 25.588(2) æ, b = 104.88(1)8, V = 8665.6(12) æ3, Z = 4, R1(F)/wR2(F2) = 0.143/0.343 for 10213/18169 reflections and 1710 parameters. C90(45)(CF3)16·1.43 C6H4CH3 : monoclinic, P21/c, a = 13.622(1) æ, b = 14.203(1) æ, c = 41.953(4) æ, b = 93.31(1)8, V = 8103.2(11) æ3, Z = 4, R1(F)/ wR2(F2) = 0.150/0.363 for 12223/16633 reflections and 1576 parameters. C90(45)(CF3)18·0.8 p-C6H4(CH3)2 : monoclinic, C2/c, a = 46.108(4) æ, b = 18.420(1) æ, c = 21.321(1) æ, b = 115.624(8)8, V = 16327(2) æ3, Z = 8, R1(F)/ wR2(F2) = 0.084/0.205 for 7294/16318 reflections and 1729 parameters. CCDC 1401674 (C90(30)(CF3)14), 1401675 (C90(35)(CF3)16), 1401676 (C90(35)(CF3)18), 1401677 (C90(45)(CF3)16), and 1401678 (C90(45)(CF3)18) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre.
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[13] a) S. I. Troyanov, E. Kemnitz, Eur. J. Org. Chem. 2003, 3916; b) M. A. Lanskikh, N. B. Tamm, L. N. Sidorov, S. I. Troyanov, Inorg. Chem. 2012, 51, 2719; c) E. Kemnitz, S. I. Troyanov, Angew. Chem. Int. Ed. 2009, 48, 2584; Angew. Chem. 2009, 121, 2622; d) S. Yang, T. Wei, E. Kemnitz, S. I. Troyanov, Chem. Asian J. 2014, 9, 79. [14] a) N. B. Tamm, L. N. Sidorov, E. Kemnitz, S. I. Troyanov, Angew. Chem. Int. Ed. 2009, 48, 9102; Angew. Chem. 2009, 121, 9266; b) M. A. Lanskikh, Yu. M. Belova, N. B. Tamm, K. Chang, E. Kemnitz, S. I. Troyanov, Crystallogr. Rep. 2011, 56, 1047.
Manuscript received: May 20, 2015 Accepted article published: June 10, 2015 Final article published: June 25, 2015
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Communication
Fullerenes
Capturing C90 Isomers as CF3 Derivatives: C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18 Nadezhda B. Tamm and Sergey I. Troyanov*[a] Abstract: High-temperature trifluoromethylation of a C90 isomeric mixture with CF3I followed by HPLC separation of C90(CF3)n isomers resulted in the isolation of several individual C90(CF3)14¢18 compounds. Single crystal X-ray diffraction with the use of synchrotron radiation resulted in the structure determination of C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18. Their addition patterns are discussed and compared with the known isomers C90(30)(CF3)18 and C90(35)(CF3)14, respectively. The presence of the most stable C90 isomer, C90(45), in the fullerene soot has been confirmed for the first time.
The investigation of the chemistry of higher fullerenes and even their identification is hampered by the low abundance in the fullerene soot, by the existence of numerous cage isomers, and the difficulties of their separation. The classical identification method by 13C NMR spectroscopy fails for higher fullerenes above C90.[1] Direct X-ray diffraction methods are useful, if the cage mobility (rotation or libration) is restrained by cocrystallization, for example, with metal porphyrinates.[2] Derivatization of higher fullerenes followed by separation of derivatives and their structural investigation proved its efficiency not only for identification but also for investigation of higher fullerene reactivity in cases of C76–C90,[3a,b] C94,[3c] C96,[3d] and C100.[3e] Because of elaborated synthesis and separation methods, most investigated are chlorido and perfluoroalkyl derivatives of higher fullerenes. C90 fullerene has 46 topologically possible IPR (isolated pentagon rule)-obeying isomers.[4] In an early 13C NMR spectroscopic study of a C90 fraction, the presence of at least five C90 isomers with C1 (one), C2 (three), and C2v (one) symmetry was suggested, however, without any further assignment.[5] X-ray diffraction studies allowed unambiguous identification of isomers D5h-C90(1), C1-C90(30), and C1-C90(32) (isomer numbers in parentheses according to the spiral algorithm[4]) as co-crystals with NiII(OEP) (OEP = octaethylporphyrin).[6a,b] The cage connec-
[a] Dr. N. B. Tamm, Prof. Dr. S. I. Troyanov Chemistry Department Moscow State University Leninskie gory, 119991, Moscow (Russia) E-mail: [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201500521. Chem. Asian J. 2015, 10, 1622 – 1625
tivity of D5h-C90(1) was also confirmed by a single-crystal X-ray study of a solvate with CS2.[6c] A trifluoromethylated derivative of C90, C90(CF3)12, was suggested to contain a C1-C90(32) cage on the basis of its 19F NMR spectrum.[3a] Recently, two other CF3 derivatives, C90(30)(CF3)18 and C90(35)(CF3)14, have been isolated and crystallographically characterized.[7] Single-crystal X-ray investigations of C90 chlorides, C90Cl22¢32, evidenced the presence of six C90 isomers, C2C90(28), C1-C90(30), C1-C90(32), Cs-C90(34), Cs-C90(35), and C2vC90(46), in the fullerene soot.[8] It was found that high-temperature chlorination of C2-C90(28) can proceed under cage shrinkage via a C2 loss and formation of chlorides with a non-classical (NC) cage, C88(NC)Cl22/24.[9] Several theoretical calculations have been performed to establish the relative stability of C90 isomers and estimate their relative populations in the experimental mixtures.[10] According to ref. [10a], the stability of C90 isomers in the ground state decreases in the order: 45, 46, 35, 18, and 9. Based on both thermodynamic and kinetic stabilities computed at the B3LYP/631G level, a somewhat different order of stability, 45, 46, 35, 30, 28, 40, 32, was concluded.[10b] Later on, a different stability sequence, 45 > 46 1 35 > 30 32 > 28 > 29 31 > 27 34, was obtained by using the PM3 method.[10c] It is noteworthy that most of the theoretically predicted isomers have been experimentally confirmed except the most stable C2-C90(45). The present communication further contributes to the chemistry of C90 isomers. Trifluoromethylation of a mixture of C90 isomers followed by HPLC separation and X-ray diffraction study allowed structural characterization of C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18. Significantly, while other CF3 and chlorido derivatives of C90(30) and C90(35) were known from previous studies, isomer C90(45) has been captured for the first time, thus evidencing the presence of the most stable C90 isomer in the fullerene soot. Trifluoromethylation of a C90 HPLC fraction with gaseous CF3I was carried out in a quartz ampoule at 450 8C for 1.5 h following a procedure described previously.[11] The product containing C90(CF3)14-18 was dissolved in n-hexane and subjected to HPLC separation using a Buckyprep column (10 Õ 250 mm, Nacalai Tesque Inc.) and n-hexane as the eluent at a flow rate of 4.6 mL min¢1. A total of 5 of the 32 fractions, with retention times of 4–85 min (see the Supporting Information for more details), gave small crystals upon recrystallization from toluene or p-xylene. An X-ray diffraction study with the use of synchrotron radiation revealed the structures of C90(30)(CF3)14,
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Communication C90(35)(CF3)16/18, C90(45)(CF3)16, and C90(45)(CF3)18, the latter containing an admixture of C90(46)(CF3)18.[12] Three of five structurally characterized C90(CF3)n molecules, C1-C90(30)(CF3)14, C1-C90(35)(CF3)16, and C1-C90(45)(CF3)16, are shown in Figure 1. While the carbon cage of C1-C90(30) is asymmetric, the cages of Cs-C90(35) and C2-C90(45) possess mirror
Figure 3. Schlegel diagrams of C1-C90(35)(CF3)16 and Cs-C90(35)(CF3)18. Cage pentagons are highlighted with gray. Black triangles denote the positions of the attached CF3 groups. Isolated benzenoid rings and isolated C=C bonds are also indicated. The Schlegel diagram of the known C1-C90(35)(CF3)14[7] corresponds to that of C1-C90(35)(CF3)16 after removal of two CF3 groups encircled by a small oval.
Figure 1. Views of the C1-C90(30)(CF3)14, C1-C90(35)(CF3)16, and C1-C90(45)(CF3)16 molecules; the latter two are presented parallel to the mirror plane and the C2 axis of the corresponding carbon cages, respectively.
and C2 axial symmetry, respectively. Symmetry lowering of the whole C90(CF3)16 molecules results from asymmetric additions of CF3 groups. The addition of two CF3 groups in CsC90(35)(CF3)18 restores mirror symmetry, whereas the C1C90(45)(CF3)18 molecule remains asymmetric. Schlegel diagrams of C1-C90(30)(CF3)14 and the known C1C90(30)(CF3)18 molecule[7] are shown in Figure 2. The addition
Figure 2. Schlegel diagrams of C1-C90(30)(CF3)14 and the known C1C90(30)(CF3)18.[7] Cage pentagons are highlighted with gray. Black triangles denote the positions of the attached CF3 groups. Nearly isolated benzenoid rings and isolated C=C bonds are also indicated.
patterns of both molecules contain 12 common positions of CF3 attachment so that the former is nearly a substructure of the latter. All CF3 groups in the C1-C90(30)(CF3)14 molecule are attached in para positions in C6(CF3)2 hexagons. Its addition pattern contains a nearly isolated benzenoid ring and one isolated C=C bond, whereas there are three isolated C=C bonds in the C1-C90(30)(CF3)18 molecule. Schlegel diagrams of the C1-C90(35)(CF3)16 and CsC90(35)(CF3)18 molecules are presented in Figure 3. The addition pattern of C1-C90(35)(CF3)16 contains two isolated C=C bonds and two benzenoid rings, one of which (the outer hexagon) is nearly isolated. The mirror symmetrical addition pattern of the Cs-C90(35)(CF3)18 molecule has two benzenoid rings and three Chem. Asian J. 2015, 10, 1622 – 1625
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isolated C=C bonds. The addition pattern of the known C1C90(35)(CF3)14[7] can be produced from that of C1-C90(35)(CF3)16 by the removal of two CF3 groups which are indicated in Figure 3. Therefore, three C90(35)(CF3)14/16/18 molecules are related with each other by simple addition (removal) of two CF3 groups which allows the suggestion that the lower derivatives are precursors of the higher ones in the course of trifluoromethylation. Similar relations have been reported for the experimentally isolated isomers of C84(22)(CF3)12/14/16,[11a] C84(23)(CF3)10/12,14/16,[11b] and C88(33)(CF3)16/18/20.[11c] Figure 4 shows Schlegel diagrams of the C1-C90(45)(CF3)16 and C1-C90(45)(CF3)18 molecules which are the first experimental evidence of the presence of isomer C2-C90(45) in the fullerene
Figure 4. Schlegel diagrams of C1-C90(45)(CF3)16 and C1-C90(45)(CF3)18. Cage pentagons are highlighted with gray. Black triangles denote the positions of the attached CF3 groups. Isolated benzenoid rings and isolated C=C bonds are also indicated. Dashed lines on the Schlegel diagram of C1-C90(45)(CF3)18 indicate the alternative position of the isolated C=C bond due to the presence of C1-C90(46)(CF3)18 in the same crystallographic site.
soot. The addition pattern of C1-C90(45)(CF3)16 is characterized by the presence of two benzeniod rings (one is partially isolated) and two isolated C=C bonds, whereas the C1-C90(45)(CF3)18 molecule contains three benzenoid rings (two are partially isolated) and three isolated C=C bonds. The attachment positions of 14 CF3 groups are common in both molecules. In C1C90(45)(CF3)18, the average C¢C bond length of benzenoid rings is 1.397 æ; the average length of C=C bonds is 1.32 æ. The structure determination of C1-C90(45)(CF3)18 revealed that one of the isolated C=C bonds is disordered between two positions related by a rotation by approximately 908 which re-
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Communication sembles a Stone–Wales rearrangement (SWR) in the carbon cage (dashed lines on the Schlegel diagram). In fact, the disorder of a C=C bond indicates the presence of a C90(46)(CF3)18 molecule in the same crystallographic site (with ca. 30 % occupancy). While the carbon cages of C2-C90(45) and C2v-C90(46) are connected by one SWR, the addition patterns of all 18 CF3 groups are exactly the same. Thus, similar shapes of both molecules are responsible for identical (or very close) retention times during HPLC separation and for their capability for mutual substitution in the crystal packing. Similar co-crystallization phenomena of the derivatives of higher fullerenes with the same addition patterns but different cage isomers have been also found in the crystal structures of C78(2,3)Br18,[13a] C84(11,14,16)Cl22,[13b] C90(34,46)Cl32,[13c] and C104(811,812)Cl24.[13d] A comparison of the molecular structures of C90(CF3)14¢18 with carbon cages of C90(30), C90(35), and C90(45) demonstrates some common features of their addition patterns. Most of additions of CF3 groups occur in para positions with the formation of chains of adjacent C6(CF3)2 hexagons. The length of the chains is limited because further addition in a para position would require an attachment to the carbon atoms in THJs (triple hexagon junctions), which is energetically unfavorable. The stabilizing factor is the formation of one, two or three isolated C=C bonds in the molecules with 14, 16, or 18 attached CF3 groups, respectively. Further stabilization occurs due to formation of aromatic substructures, isolated or nearly isolated benzenoid rings, on the carbon cages. The addition patterns of the C90(CF3)14,16,18 molecules exhibit similar features as the most extensively studied CF3 derivatives of C84 (isomers 16, 18, 22, and 23), in which the addition to THJ has not been observed.[11] However, the addition of two CF3 groups in THJs was established in the overcrowded molecule of C94(61)(CF3)20.[14a] Several C76(1)(CF3)14¢18 molecules contain one or two CF3 groups in THJs.[14b] In the latter cases, the presence of additions in THJs can be explained by the simultaneous formation of isolated benzenoid rings or/and isolated butadiene fragments on the C76 carbon cage. An important result of the present work is the first confirmation of the presence of isomer C90(45) in the fullerene soot, which was highly expected to be isolated experimentally as the most stable isomer of C90 according to quantum chemical calculations by different methods.[10] Now the set of seven experimentally confirmed isomers of C90 includes all isomers of high (nos. 45, 46, 1) or middle relative stability (nos. 35, 30, 32, 28).[10c] Interestingly, carbon cages of these isomers (except D5hC90(1)) are interconnected by only one or two SWRs of the pyracylene type.[1, 8] In particular, two-step pathways between isomers C90(30), C90(35), and C90(45) include isomer C1-C90(32) as an intermediate cage. Isomer C90(46) can be transformed into C90(35) or C90(45) by only one SWR, the latter pathway having been discussed above and shown in Figure 4. In summary, the high-temperature trifluoromethylation of a C90 isomeric mixture with CF3I followed by HPLC separation of C90(CF3)n isomers resulted in the isolation and structure determination of several CF3 derivatives of C90(30), C90(35), and C90(45) with 14–18 attached CF3 groups. Therefore, the structural chemistry of trifluromethylated isomers of C90 is signifiChem. Asian J. 2015, 10, 1622 – 1625
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cantly extended allowing the formulation of general rules concerning their addition patterns. More importantly, isomer C90(45) has been captured as two CF3 derivatives, thus confirming the earlier predictions about its presence in the fullerene soot based on its highest relative stability among the 46 topologically possible isomers of C90 fullerene. It is also remarkable that isomer C90(45) has been captured as a result of trifluoromethylation and HPLC separation, but not by the chlorination method, which was widely used for the first identification of numerous isomers of higher fullerenes.
Acknowledgements This work was supported by the the Russian Foundation for Basic Research (15-03-04464 and 13-03-91332). Keywords: C90 · fullerenes · HPLC · structure elucidation · trifluoromethylation [1] T. Minami, Y. Miyake, K. Kikuchi, Y. Achiba in The 18th Fullerene General Symposium, The Fullerene Research Association of Japan, Okazaki, 2001, p. 42. [2] a) Z. Wang, H. Yang, A. Jiang, Z. Liu, M. M. Olmstead, A. L. Balch, Chem. Commun. 2010, 46, 5262; b) H. Yang, H. Jin, Y. Che, B. Hong, Z. Liu, J. A. Gharamaleki, M. M. Olmstead, A. L. Balch, Chem. Eur. J. 2012, 18, 2792. [3] a) I. E. Kareev, A. A. Popov, I. V. Kuvychko, N. B. Shustova, S. F. Lebedkin, V. P. Bubnov, O. P. Anderson, K. Seppelt, S. H. Strauss, O. V. Boltalina, J. Am. Chem. Soc. 2008, 130, 13471; b) K. S. Simeonov, K. Yu. Amsharov, M. Jansen, Chem. Eur. J. 2008, 14, 9585; c) N. B. Tamm, S. Yang, T. Wei, S. I. Troyanov, Inorg. Chem. 2015, 54, 2494; d) S. Yang, T. Wei, E. Kemnitz, S. I. Troyanov, Angew. Chem. Int. Ed. 2012, 51, 8239; Angew. Chem. 2012, 124, 8364; e) M. A. Fritz, E. Kemnitz, S. I. Troyanov, Chem. Commun. 2014, 50, 14577. [4] P. W. Fowler, D. E. Manolopoulos, An Atlas of Fullerenes, Clarendon Press, Oxford, UK, 1995. [5] Y. Achiba, K. Kikuchi, Y. Aihara, T. Wakabayashi, Y. Miyake, M. Kainosho in The Chemical Physics of Fullerenes 10 (and 5) Years Later (Ed.: W. Andreoni), Kluwer, Dordrecht, 1996, p. 139. [6] a) H. Yang, C. M. Beavers, Z. Wang, A. Jiang, Z. Liu, H. Jin, B. Q. Mercado, M. M. Olmstead, A. L. Balch, Angew. Chem. Int. Ed. 2010, 49, 886; Angew. Chem. 2010, 122, 898; b) H. Yang, B. Q. Mercado, H. Jin, Z. Wang, A. Jiang, Z. Liu, C. M. Beavers, M. M. Olmstead, A. L. Balch, Chem. Commun. 2011, 47, 2068; c) F. L. Bowles, B. Q. Mercado, K. B. Ghiassi, M. M. Olmstead, H. Yang, Z. Liu, A. L. Balch, Cryst. Growth Des. 2013, 13, 4591. [7] N. B. Tamm, S. I. Troyanov, Nanosyst. Phys. Chem. Math. 2014, 5, 39. [8] S. I. Troyanov, S. Yang, C. Chen, E. Kemnitz, Chem. Eur. J. 2011, 17, 10662. [9] I. N. Ioffe, O. N. Mazaleva, L. N. Sidorov, S. Yang, T. Wei, E. Kemnitz, S. I. Troyanov, Inorg. Chem. 2013, 52, 13821. [10] a) Z. Slanina, X. Zhao, S.-L. Lee, E. O˜sawa, Scr. Mater. 2000, 43, 733; b) G. Sun, Chem. Phys. 2003, 289, 371; c) M. Watanabe, D. Ishimaru, N. Mizorogi, M. Kiuchi, J. Aihara, THEOCHEM 2005, 726, 11. [11] a) K. Chang, M. A. Fritz, N. B. Tamm, A. A. Goryunkov, L. N. Sidorov, C. Chen, S. Yang, E. Kemnitz, S. I. Troyanov, Chem. Eur. J. 2013, 19, 578; b) N. A. Romanova, M. A. Fritz, K. Chang, N. B. Tamm, A. A. Goryunkov, L. N. Sidorov, C. Chen, S. Yang, E. Kemnitz, S. I. Troyanov, Chem. Eur. J. 2013, 19, 11707; c) M. A. Lanskikh, K. Chang, N. B. Tamm, E. Kemnitz, S. I. Troyanov, Mendeleev Commun. 2012, 22, 136. [12] Synchrotron X-ray data were collected at 100 K at the BESSY storage ring (BL14.2, PFS, Berlin, Germany) using a MAR225 CCD detector; l = 0.8950 and 0.8856 æ. C90(30)(CF3)14·0.5 C6H5CH3 : triclinic, P1¯, a = 14.192(1) æ, b = 19.861(1) æ, c = 29.348(3) æ, a = 93.080(10)8, b = 91.614(10)8, g = 104.479(10)8, V = 7990.5(11) æ3, Z = 4, R1(F)/wR2(F2) = 0.195/0.448 for 13169/29035 reflections and 2736 parameters. C90(35)(CF3)16·1.86 C6H5CH3 : monoclinic, C2/c, a = 24.051(1) æ, b =
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Communication 15.568(1) æ, c = 43.921(3) æ, b = 97.034(6)8, V = 16321.4(17) æ3, Z = 8, R1(F)/wR2(F2) = 0.117/0.210 for 6189/17612 reflections and 1536 parameters. C90(35)(CF3)18·1.17 p-C6H4(CH3)2 : monoclinic, P21/c, a = 14.278(1) æ, b = 24.542(2) æ, c = 25.588(2) æ, b = 104.88(1)8, V = 8665.6(12) æ3, Z = 4, R1(F)/wR2(F2) = 0.143/0.343 for 10213/18169 reflections and 1710 parameters. C90(45)(CF3)16·1.43 C6H4CH3 : monoclinic, P21/c, a = 13.622(1) æ, b = 14.203(1) æ, c = 41.953(4) æ, b = 93.31(1)8, V = 8103.2(11) æ3, Z = 4, R1(F)/ wR2(F2) = 0.150/0.363 for 12223/16633 reflections and 1576 parameters. C90(45)(CF3)18·0.8 p-C6H4(CH3)2 : monoclinic, C2/c, a = 46.108(4) æ, b = 18.420(1) æ, c = 21.321(1) æ, b = 115.624(8)8, V = 16327(2) æ3, Z = 8, R1(F)/ wR2(F2) = 0.084/0.205 for 7294/16318 reflections and 1729 parameters. CCDC 1401674 (C90(30)(CF3)14), 1401675 (C90(35)(CF3)16), 1401676 (C90(35)(CF3)18), 1401677 (C90(45)(CF3)16), and 1401678 (C90(45)(CF3)18) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre.
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[13] a) S. I. Troyanov, E. Kemnitz, Eur. J. Org. Chem. 2003, 3916; b) M. A. Lanskikh, N. B. Tamm, L. N. Sidorov, S. I. Troyanov, Inorg. Chem. 2012, 51, 2719; c) E. Kemnitz, S. I. Troyanov, Angew. Chem. Int. Ed. 2009, 48, 2584; Angew. Chem. 2009, 121, 2622; d) S. Yang, T. Wei, E. Kemnitz, S. I. Troyanov, Chem. Asian J. 2014, 9, 79. [14] a) N. B. Tamm, L. N. Sidorov, E. Kemnitz, S. I. Troyanov, Angew. Chem. Int. Ed. 2009, 48, 9102; Angew. Chem. 2009, 121, 9266; b) M. A. Lanskikh, Yu. M. Belova, N. B. Tamm, K. Chang, E. Kemnitz, S. I. Troyanov, Crystallogr. Rep. 2011, 56, 1047.
Manuscript received: May 20, 2015 Accepted article published: June 10, 2015 Final article published: June 25, 2015
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