Synthesis and structures of trifluoromethyl derivatives of fullerenes C84(16) and C84(18)

Abstract

Trifluoromethyl derivatives of fullerene C 84 minor cage isomers C s C 84 (16) and C 2v C 84 (18) of general formulas C 84 (16)(CF 3 ) 2m (2m = 8, 10, 12, 14, 18) and C 84 (18)(CF 3 ) 2m (2m = 10, 12) were isolated by a multi step HPLC from the products of high temperature trifluoromethyla tion of a mixture of higher fullerenes. Molecular structures of these compounds were deter mined by single crystal X ray diffraction using synchrotron radiation. The experimentally ob tained structural data and the results of quantum chemical calculations were discussed in terms of general regularities of trifluoromethylation of C 84 isomers in a wide range of compositions. The addition patterns of CF 3 groups in C 84 (16/18)(CF 3 ) 2m molecules were found to depend on particular structural features of isomeric C 84 cages.To date, the most studied is the chemistry of fullerenes C 60 and C 70 , which is primarily due to a predominance of these compounds in the fullerene soot. 1 A third predo minant (and the first among higher fullerenes) is fullerene C 84 . It is known 2 that the synthesis of fullerenes leads only to those of them which obey an empirical isolated penta gon rule (IPR), i.e. do not have adjacent five membered rings in the cage. The absence of the fused five membered rings decreases steric strain of the carbon cage of fullerenes, which leads to greater thermodynamic stability and chem ical inertness of such fullerenes, resulting in their accu mulation in the course of the synthesis.Unlike fullerenes C 60 and C 70 , each of which is repre sented by the only IPR isomer, fullerene C 84 can exist as 24 IPR isomers. 2 By now, the presence in the fullerene soot of ten different C 84 isomers is experimentally con firmed, with the D 2 C 84 (22) and D 2d C 84 (23) cage iso mers (a consecutive number of isomer according to the spiral algorithm 2 is given in parentheses) being the major representatives in accordance with their higher thermo dynamic stability. 3,4 The remaining (minor) C 84 isomers are present in much smaller amounts. 5 Fullerenes are commonly separated by HPLC, where as 13 C NMR spectroscopy is a conventional method for their identification. These means were used 6 to confirm the existence of minor isomers No. 4 (D 2d ), No. 5 (D 2 ), No. 11 (C 2 ), No. 14 (C s ), No. 16 (C s ), 5 No. 19 (D 3d ), and No. 24 (D 6h ) for fullerene C 84 . However, the 13 C NMR data showed that in this case the assignment of chromato graphic peaks of C s C 84 (14) and C s C 84 (16) isomers was not unambiguous because of the same symmetry. 5 After wards, the use of X ray diffraction method for the deter mination of the cage structures of fullerenes (only for C s C 84 (14) 7 ) or their derivatives confirmed the existence of all the indicated isomers except C 84 (19) and C 84 (24). The presence in the mixtures of C 2v C 84 (18) isomer was confirmed 8 by the crystal and molecular structures of its C 84 (18)(C 2 F 5 ) 12 derivative.Like fullerenes, their derivatives can be subjected to HPLC separation and in this case it can be more ...

Synthesis, isolation, and X-ray structural characterization of trifluoromethylated C78 fullerenes: C78(2)(CF3)10/12 and C78(3)(CF3)12/14

“…Structural relations between C 78 (2)(CF 3 ) 10 and C 78 (2)(CF 3 ) 12 molecules are very similar to those reported for C 84 (18)(CF 3 ) 10 and C 84 (18)(CF 3 ) 12 [18]. The addition pattern of C s -C 84 (18)(CF 3 ) 10 contains a single p 9 ribbon which is very similar to that in C s -C 78 (2)(CF 3 ) 10 .…”

“…Two different starting higher fullerene mixtures were used for trifluoromethylation with gaseous CF 3 I in quartz ampules following a previously described procedure [16][17][18]. The mixture of higher fullerenes C 76 -C 96 (45 mg; MER Corp.) was trifluoromethylated at 560…”

“…The addition pattern of C s -C 84 (18)(CF 3 ) 10 contains a single p 9 ribbon which is very similar to that in C s -C 78 (2)(CF 3 ) 10 . Though the experimentally determined structure of C s -C 84 (18)(CF 3 ) 12 is characterized by the attachment of twelve CF 3 groups in all pentagons (with two additional groups in a separate p-C 6 (CF 3 ) 2 hexagon), a theoretically predicted structure with a p 12 loop (84(18)/12 − 3 in [18]), i.e., an analog of C 78 (2)(CF 3 ) 12 , is only 6 kJ·mol −1 less stable so that its presence in the trifluoromethylation products of C 84 (18) cannot be excluded. In fact, the only example of addition-free pentagons in the molecule with more than 12 addends on a fullerene cage has been reported for C 88 (17)Cl 16 containing two such pentagons [21].…”

New Isolated‐Pentagon‐Rule Isomers of Fullerene C96 Captured as Chloro Derivatives

“…As has been found in the course of long standing fullerene studies, the abundance and the number of different IPR isomers which are present in the fullerene soot are larger for fullerenes containing (60 + 6 k ) carbon atoms in the cage, which was also supported by theoretical considerations . Indeed, in spite of the significant progress in the investigation of higher fullerenes in a wide range of cage sizes, the number of structurally characterized isomers of (60 + 6 k ) fullerenes such as C 84 (10 isomers),[6b], C 90 (8),[5a], [5b], [6a], [6ba], and C 96 (9)[5d], , remains larger than for their 6 n ± 2 neighbors (2–5). [3d], [6d], At present, a discovery of new isomers of higher fullerenes became a more challenging task thus requiring the use of more efficient separation and investigation methods.…”

Chloro‐ and Trifluoromethyl Derivatives of Fullerene C82, C82Cl14 and C82(CF3)14

“…A mixture of higher fullerenes C 76 −C 96 , also containing small amounts of C 60 and C 70 , (MER Corp.) was used for trifluoromethylation with gaseous CF 3 I in quartz ampoules at 530 °C as described elsewhere . Trifluoromethylation products, a mixture of fullerene(CF 3 ) n , was separated chromatographically in n ‐hexane affording fractions of trifluoromethylated fullerenes including C 82 (CF 3 ) 12‐20 (see Supporting Information for details).…”