Isolation and characterisation of C60F4, C60F6, C60F8, C60F7CF3 and C60F2O, the smallest oxahomofullerene; the mechanism of fluorine addition to fullerenes

Boltalina, Olga V., Darwish, Adam D., Street, Joan M., Taylor, Roger and Wei, Xian-Wen (2002) Isolation and characterisation of C60F4, C60F6, C60F8, C60F7CF3 and C60F2O, the smallest oxahomofullerene; the mechanism of fluorine addition to fullerenes. Journal of the Chemical Society, Perkin Transactions 2, (2), 251-256. (doi:10.1039/b108832g).

Abstract

From the reaction of [60]fullerene with K2PtF6 at 470 degreesC, we have isolated C60F4, C60F6 (mixed with C60F7CF3), C60F8 and C60F2O. The F-19 NMR spectrum of C60F2O comprises a single line at -69.3 ppm, consistent with it being the simplest oxahomofullerene. The AA'BB' spectrum for C60F4 (double doublets at -141.82 and -142.78 ppm) shows it to be isostructural with C60H4, the addends in each case being in a 1,2,3,4-arrangement. The spectrum for C60F6 consists of doublets at -124.39 and -142.41 and a triplet at -139.78 ppm (coupling confirmed by a 2D spectrum), showing the fluorines to be in a previously-conjectured S-shaped motif, giving the molecule overall C-2 symmetry. The C60F8 spectrum comprises five peaks in a 1 : 2 : 2 : 2 : 1 ratio, so that the molecule has C-s symmetry based on a T-shaped motif, also conjectured previously. The peak couplings and symmetry indicate that the structure is created by addition of three pairs of fluorines across contiguous double bonds, followed by 1,8-addition of the final fluorine pair; this unique latter step is attributed to the ability of a pentagon containing three sp(3) carbons to accommodate a double bond, due to the reduction in strain. The C60F8 structure is part of the motif of C60F16 and C60F18, indicating it to be an intermediate on the pathway to formation of these compounds. The spectrum for C60F7CF3 shows the presence of one major and one minor isomer, the probable structures of which are deduced.

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