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Fragmentation of the 60 fullerene cage during bromination
No full textHeating [60]fullerene with Br-2/FeCl3/benzene under reflux for 24 h yields in addition to the previously observed phenylated fullerenes, two bromine-containing open-cage products of 768/770 and 848 amu, each of which fragments to decacyclene during El mass spectrometry. This provides an example of the reverse of the [60]fullerene synthesis from aromatic precursors
Electrophilic substitution of C60F18 into phenols: HF elimination between OH and a 1,3-shifted fluorine giving benzofurano[2',3':10,26]hexadecafluro[60]fullerene and derivatives
No full textThe reaction of C60F18 with phenol, 2-naphthol and quinol in the presence of ferric chloride leads to initial electrophilic substitution (aryldefluorination). This occurs at both ortho and para positions for phenol, at the ortho position for quinol, and at the relatively hindered but most reactive 1-position for 2-naphthol. It is followed, where sterically favourable, by HF loss either between the OH group and F (rendered adjacent as a result of a 1,3-shift) or to attack of the OH group at an adjacent double bond with loss of a beta-fluorine, giving benzofurano[2',3':10,26]hexadecafluoro[60]fullerene derivatives. The reaction is accompanied by some complete defluorination leading, in reaction with phenol and with 2-naphthol, to the formation of benzofurano[2',3':1,2][60]fullerene and naphtho[2,1:b]furano[d:1,2][60]-fullerene, respectively. The mechanism of base-catalysed reaction of phenols with C60Cl6 is re-evaluated
Isolation and characterisation of C60F4, C60F6, C60F8, C60F7CF3 and C60F2O, the smallest oxahomofullerene; the mechanism of fluorine addition to fullerenes
No full textFrom 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
C60F14OFPh3, a fluoroxy derivative of C60F15Ph3; evidence for the presence of 'missing' fluorine through restricted rotation of a phenyl group
No full textFrom the reaction of C60F18 with benzene in the presence of SbCl5 we have isolated a compound of 1252 amu indicated to be C60F14OFPh3, a fluoroxyfullerene. Temperature-variable H-1 NMR shows that one phenyl group suffers restricted rotation on cooling to 218 K, attributed to the presence of the OF group which, as in the case of the recently characterised C60F17OF, fails to give a signal for this group in the F-19 NMR. We have isolated also, C60F14O2FPh3 (1268 amu) a mixture of oxahomo derivatives Of C60F14OFPh3 arising from oxygen insertion into FC-CF bonds. Theoretical calculations for C60F14OFPh3 indicate that the phenyl group nearest to the OF group is twisted out of the plane containing the other two
C2 isomers of C84F40 and C84F44 are cuboid and contain benzenoid and naphthalenoid aromatic patches
No full textA 1:1 mixture of C84F40 and C84F44, both derived from the D2(IV) isomer, has been isolated from the fluorination of [84]fullerene with either MnF3 or CoF3 at 500 °C. The 1D and 2D COSY 19F NMR spectra showed that each derivative is cuboid, having benzenoid rings at four of the six octahedral sites; the two remaining sites have naphthalenoid rings for C84F40, and two slightly offset benzenoid rings for C84F44. The benzenoid rings each have six adjacent sp3-hybridised carbon atoms whilst the naphthalenoid moieties have eight, thus facilitating full delocalisation. In terms of the number and size of aromatic patches, C84F44 is the most aromatic fullerene derivative yet isolated
Formation of methylene derivatives of [60]-, [70]-, [78]- and [84]-fullerenes by reaction of fullerene-containing soot extract with tetrahydrofuran
No full textIf a mixture of carbon clusters extracted from soot produced by the arc-discharge procedure is either heated or sonicated with tetrahydrofuran (THF), a range of methylene derivatives Cm[CH2]n, where m is 60, 70, 78 or 84 and n is variously 1-6 are produced. These results constitute the first formation of [78]fullerene derivatives; [76]fullerene does not appear to react under these conditions. Species with n = 3 are dominant, believed to be due to addition of trimethylene chains, through loss of formaldehyde from THF. This conclusion is supported by the prominence of [CH2]4 adducts in the product if [60]fullerene is heated under reflux with dihydropyran. Reaction of pure [60]fullerene with THF results in the addition of up to 10 methylene groups to the cage.</p
Polyhydrogenation of [60]- and [70]-fuilerenes
No full textReduction with Zn-conc. HC1 in either benzene or toluene solution, results in rapid and quantitative conversion of [60]- and [70]-fullerenes into mainly C60H36 and C70H36/38. Significant amounts of more highly hydrogenated derivatives are also formed. Mass spectra under EI conditions can be obtained free of peaks due to either less-hydrogenated species or the parent fullerenes, provided they are obtained immediately, since both compounds undergo rapid light-catalysed degradation in the presence of oxygen, to give the parent fullerenes, oxygen-containing derivatives (fullerenols) and lower hydrides; C60H18 is the main product from C60H36. Formation of reduced fullerenes up to C60D44 and C70D48 on reaction of [60]- and [70]-fullerenes with Zn-conc. DCl, is attributed to the higher stability of CD compared with C-H bonds, which provides greater compensation for the loss of resonance energy and the greater steric compression that accompanies reduction beyond the 36 H level. Laser-desorption time-of-flight mass spectrometry indicates that the absence of the corresponding higher hydrides (as opposed to deuterides) is not due to decomposition during EI mass spectrometry. The hydrides do not undergo hydrogen exchange with D2O either alone or in the presence of either sodium hydrogen carbonate or sodium hydroxide. C60H36 has considerable thermal stability but that for C70H36/38 is lower. HPLC chromatograms, as well as IR, UV-VIS,1H NMR, and mass spectra have been obtained for both compounds. Each appears to be highly resistant to further reduction by hydrogen-catalyst, but shows a surprising tendency to form trimethylene adducts, by an unknown mechanism.</p
Arylation of [60]fullerene with Br<sub>2</sub>/FeCl<sub>3</sub>/PhH: Formation of C<sub>58</sub> derivatives via CO loss
No full textHeating a mixture of [60]fullerene, bromine, ferric chloride and benzene under reflux for 24 h produces a range of phenylated [60]fullerene derivatives. The main product is C60Ph5H, but other components identified by mass spectrometry (and in some cases separated by HPLC) are: C60Phn (n = 4, 6, 8, 10, 12), C60PhnO2 (n = 4, 6, 8, 10, 12), C60PhnOH (n = 7, 9, 11), C60PhnH2 (n = 4, 10), C60Ph4H4, C60Ph5H3, C60PhnO2H (n = 5, 9), C60Ph4C6H4O2, C60Ph9OH3, and C60Ph11O3H2. In the corresponding reaction with toluene, the crude reaction mixture contained C60(MeC6H4)4 as a main product; C60(ClC6H4)5H was obtained from the reaction with chlorobenzene. Formation of these derivatives is believed to involve radical bromination of the fullerene, followed by electrophilic substitution of the halogenofullerene into the aromatic, accompanied in some case by hydrolysis, elimination and epoxide formation; oxidation may also introduce ketone/dioxetane functionality. The EI mass spectra of C60Ph4O2 and C60Ph8O2 show degradation to C58Phn (n = 0 - 8), having structures believed to be related to the pseudofofullerenes C68Phn (n = 0 - 8) reported recently. These results suggest that some derivatisations of fullerenes confer stability, due to the relief of strain.</p
Formation of [18]trannulenes derived via Bingel reactions between C60F18O isomers and CHBr(CO2Et)(2) and between C60F18 and CHX(CO2R)(2) (X = Br, Cl; R = Me, Et)
No full textThrough extended S(N)2' nucleophilic substitution of three fluorine atoms in two isomers of C60F18O by alkyl halogenomalonate anions -CBr(CO2Et)(2), (obtained from diethyl bromomalonate in the presence of DBU) we have prepared and characterised the [18]trannulenes, C60F15O[CBr(CO2Et)(2)](3). Likewise we have prepared [18]trannulenes by the reactions between C60F18 and either -CBr(CO2Me)(2) or -CCl(CO2Et)(2) (obtained from the corresponding esters 1, 2 and DBU). The formation of the trannulenes from either 1 or 2 shows that the CBr(CO2Me)(2) and CCl(CO2Et)(2) substituents, though smaller than CBr(CO2Et)(2) are still large enough to bring about the extended S(N)2' substitution, rather than direct nucleophilic substitution. The products from the oxides show that oxygen does not inhibit trannulene formation either sterically or electronically. Each derivative has the brilliant emerald-green colour of the corresponding [18]trannulene prepared from C60F18 and diethyl bromomalonate, arising from the presence of bands at ca. 615 and 660 nm; minor variations in wavenumber and relative intensities occur according to the derivative. Under less forcing conditions, mono- and bis-substitution products were obtained from the more available symmetrical oxide and from the reaction of the chloro- and bromo-esters with C60F18
Reaction of [70]fullerene with benzyne
No full textUp to ten equivalents of benzyne can be added to [70]fullerene; the possible sites of addition are considered.</p
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