Adam D. Darwish

FORMATION OF C70PH10 AND C70PH8 FROM THE ELECTROPHILE C70CL10

In the presence of ferric chloride, benzene readily undergoes electrophilic substitution by C70Cl10 to give both yellow C70Ph10 and orange-red C70Ph8, each of which is luminescent. Their structures have been characterised by 1H and 13C NMR spectroscopy [including nOe and two-dimensional (COSY) analysis], and by UV, IR, and mass spectrometry. C70Ph10 is not formed directly from C70Cl10, but rather by further phenylation of the intermediate C70Ph8. The adjacent phenyl groups of C70Ph10 are sterically prevented from rotating at room temperature.

Formation of fullerols via hydroboration of fullerene–C60

Reaction of fullerene–C60 with an excess of BH3–THF complex followed by hydrolysis with either glacial acetic acid, sodium hydroxide/hydrogen peroxide or sodium hydroxide gives water soluble fullerols; oxidation of initially formed C–H bonds is believed to accompany the reaction.

Preparation and 13C NMR spectroscopic characterisation of C60Cl6

Reaction of an excess of iodine monochloride with C60, in either benzene or toluene at room temperature, gives a quantitative yield of C60Cl6, the 13C NMR spectrum of which indicates that it is isostructural with C60Br6.

Phosphorus/buckminsterfullerene intercalation compounds, C60(P4)2

Abstract A novel crystalline compound has been made by combining the two elements, carbon and phosphorus, that form isolated cage allotropes. The material, C 60 (P 4 ) 2 , which consists of disordered tetrahedral P 4 molecules intercalated in a hexagonal C 60 crystal lattice has been prepared by both gas—solid reaction and co-precipitation from benzene solution.

Polyhydrogenation of [60]- and [70]fullerenes with Zn/HCl and Zn/DCl

Abstract Previous work on polyhydrogenation of fullerenes leading to C 60 H 36 and C 70 H 36 as the main products is reviewed. The most probable structures of these species, based on their aromaticities, are presented. Zinc/concentrated HCl is shown to be an excellent and rapid reducing agent for benzene or toluene solutions of fullerenes at room temperature. The polyhydrogenated species are unstable towards light and undergo oxidative degradation, with, in the case of C 60 H 36 , formation of C 60 H 18 as an intermediate. Reduction of these fullerenes by zinc/concentrated DCl gives C 60 H 44 and C 70 H 48 as the highest hydrogenated products; the greater incorporation of deuterium is attributed to the greater C-D bond energy. In the absence of light and oxygen, C 60 H 36 exhibits high thermal stability. Attempted further reduction of C 60 H 36 leads to formation of trimethylene adducts; these are also formed on reduction of [84] fullerenes which gives C 84 H 48 as the main product.

Synthesis and characterisation of the methanofullerenes, C60(CHCN) and C60(CBr2)

Abstract Two new methanofullerenes, C 60 (CHCN) and C 60 (CBr 2 ), have been prepared by treating a mixture of [60]fullerene and either CH 2 BrCN or CHBr 3 respectively with LDA. The products were purified by silica gel column chromatography, characterised by EI-MS and IR, and shown by 13 C NMR to consist solely of 6-6 ring junction adducts.

Formation and characterisation of C70Cl10

[70]Fullerene reacts with ICl in benzene to give C70Cl10, shown by 13C NMR spectroscopy to have Cs symmetry with chlorines located around the cage waist.

Polyhydrogenation of [60]- and [70]-fullerenes

Reduction with Zn–conc. HCl 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. DCI, is attributed to the higher stability of C–D 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.

The Structure of Buckminsterfullerene Compounds

An understanding of the principles required for the preparation of pure buckminsterfullerene (C60) derivatives of known addition number and pattern, and C60 containing materials of known composition and structure, is necessary for the development of C60 chemistry. Single crystal X-ray diffraction is a powerful tool for the determination of the structures of C60 compounds, seven examples of which are described here. C60 is brominated by Br2 in a variety of solvents to give either C60Br6 or C60Br8, depending upon the particular solvent used. Crystals of C60Br6.Br2.CCl4 (1), C60Br6.xBr2 (x ≈ 2) (2), and C60Br8.xBr2 (x ≈2) (3) are obtained from CCl4, C6H6, and CS2 respectively. Cocrystallization of C60 and I2 from C6H5CH3 solution yields the intercalate C60.I2.C6H5CH3 (4), and slow evaporation of C6H6 solutions of C60 gives crystals of the solvate C60.4C6H6 (5). Mixing of saturated C6H6 solutions of C60 and η5-C5H5)2Fe gives a dark red solution from which black crystals of C60.[(η5-C5H5)2Fe]2 (6) are deposited. In a similar manner cocrystallisation of C60 and (η5-C5H5)4Fe4(CO)4 from C6H6 solution yields black crystals of the intercalate C60.(η5-C5H5)4Fe4(CO)4.3C6H6 (7).

[60]- and [70]Fullerenes are trifluoromethylated across 5 : 6-bonds

Trifluoromethylation of [60]- and [70]fullerenes occurs across both 6:6- and 5:6-bonds giving unsymmetrical tetramethyl adducts having four contiguous CF3 groups; both fullerenes give bis adducts which do not involve 6:6-addition, and unsymmetrical hexa-adducts (with contiguous CF3 groups) are also obtained from [60]fullerene.