Multinuclear N M R spectroscopy and conductivity measurements showed that the 1 -ethyl-3-methylimidazolium cation, [emim] +, not only forms strong hydrogen bonds (using all three ring protons H2, H4 and H5) with halide ions in polar molecular solvents (e.g. ethanenitrile) and ionic liquids, but that it exists in a quasi-molecular state, [emim]X, in non-polar solvents (e.g. trichloro-and dichloromethane), showing a conventional aromatic stacking phenomenon.Over the past ten years the perception of the ability of the 1ethyl-3-methylimidazolium cation, [emim] + , 1,2 to enter into hydrogen bonds with halide ions has developed from not p ~s s i b l e , ~ through contr~versial,~ to widely a ~c e p t e d . ~. ~ However, the strongest evidence for these claims has always rested upon solid-state X-ray crystallographic determinations of the structures of both [emim]+ 4,7 and [edmim]+ (edmim = 1ethyl-2,3-dimethylimidazolium) salts.* A number of first-class solution studies have been reported, 5*6*9 yet no incontrovertible evidence has yet been presented that the [emim]' cation is capable of forming hydrogen bonds in solution. Proton NMR spectra of room-temperature [emim]C1-A1C13 ionic liquids are known to be very composition dependent, particularly in the basicIn particular, the H2 proton is very sensitive, moving significantly upfield with increasing acidity. This has been widely interpreted in terms of a stacked oligomeric model 3,5 in which anions and cations alternate, the anions being associated with the imidazolium ring both directly above and below its plane. Nevertheless, a 'H NMR study l 1 of several imidazole and imidazolium derivatives in CD,Cl, has shown that the chemical shift of the H2 proton was sensitive to the nature of the anion present, and hydrogen bonding between discrete ion pairs was postulated to explain this result. We thus decided to undertake a definitive study of the NMR characteristics of [emim]X (X = CI, Br or I) in molecular solvents, free of the aporia associated with ionic liquids. We demonstrate here, using principally the techniques of multinuclear NMR spectroscopy and conductivity measurements, that [emim] + not only forms strong hydrogen bonds (using all three ring protons H2, H4 and H5) with halide ions in polar molecular solvents (e.g. ethanenitrile, MeCN) and ionic liquids, but that it exists in a quasi-molecular state, [emim]X, in non-polar solvents (e.g. CHCl, and CH,Cl,), showing a conventional aromatic stacking phenomenon. Experiment a1N M R Studies.-Deuterium oxide (99%) was distilled in O ~U O before use; CD3CN and CD2C12 were distilled from calcium hydride under dry dinitrogen. Samples of [emim]X (X = C1, Br

Reaction of an excess of iodine monochloride with Cm, in either benzene or toluene at room temperature, gives a quantitative yield of CgoCls, the 13C NMR spectrum of which indicates that it is isostructural with CmBrs.The specific derivatisation of Cm is a key target in the development of its chemistry. Because halogeno compounds are generally important synthons, preparation and characterisation of halogenofullerenes is of particular significance.

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The potential of the heteroleptic heavier alkaline-earth hexamethyldisilazides [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ae{N(SiMe3)2}(THF)](Ae = Ca, Sr, Ba) as kinetically-stable reagents for further protolytic reaction chemistry has been assessed. Only the previously reported calcium complex was found to be stable to solution dismutation and dynamic ligand exchange. The barium complex was isolated in sufficient purity to enable characterisation by an X-ray analysis. Reactions of the kinetically robust calcium complex with cyclohexylamine and tert-butylamine resulted in displacement of THF and formation of solvated structures, which could be characterised by 1H NMR spectroscopy. Attempts to isolate these solvated complexes were unsuccessful due to redistribution to the homoleptic complex [{HC(C(Me)2N-2,6-iPr2C6H3)2}2Ca]. In contrast, the more acidic amine [H2NCH2CH2OMe] was cleanly deprotonated resulting in the isolation of the first well defined primary amido derivative of a heavier alkaline-earth element, [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{NHCH2CH2OMe}]2, which retains its dimeric constitution in solution and is stable to further intermolecular ligand exchange. Reactions of [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{N(SiMe3)2}(THF)] with a variety of ortho-disubstituted anilines also resulted in immediate protonation of the hexamethyldisilazide ligand. Only the most sterically demanding 2,6-diisopropylphenyl anilide derivative possessed sufficient kinetic stability to allow isolation of the heteroleptic complex. The crystal structure of [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{N(H)-2,6-iPrC6H3}(THF)] was shown to exist as a mononuclear, pseudo-five-coordinate complex in which the coordinative unsaturation of the calcium centre is relieved by a Ca...H-C agostic-type interaction to one of the ortho isopropyl groups of the anilide ligand. This interaction is not maintained in solution however and the complex slowly redistributes to the homoleptic beta-diketiminato species and ill-defined polymeric calcium anilido products.

Fullerene-C6, and fullerene-C,, have been reduced by various methods to di-and tetra-hydro derivatives. Reduction by diimide is the most satisfactory method with regard to both yield and ease of carrying out of the reaction. The 'H NMR chemical shifts are highly solvent dependent, and are ca. 1 ppm further downfield in carbon disulfide than in benzene; the shifts for C60Hn compounds are downfield compared with those for C, , Hn compounds, due possibly to differences in strain between the cages and/or a field effect operating across the cage void. 1,2,3,4-TetrahydrofuIlerene-C, is the main product from reduction of fullerene-C,, with diimide, and all other tetrahydro derivatives that can be produced by addition across the high order bonds appear to be present, together with more highly hydrogenated derivatives. Eight products are obtained on diimide reduction of fullerene-C,,; two have been characterised as 1 ,5,6,9-tetrahydrofullerene-C,, and 1 ,7,8,9-tetrahydrofullerene-C,,, and two others are the 1,9-and 7,8-dihydrofullerenes obtained by reduction with diborane. The other four derivatives may be the other tetrahydro isomers which can be obtained by addition across the 1,9-bond and its other equivalents. The hydrogenated fullerenes are more soluble in carbon disulfide than in either benzene or toluene, thus facilitating observation of the 13C satellites of 1,2dihydrofullerene-60 in the 'H NMR spectrum. The C-H and H-H coupling constants are 141.2 and 15.7 Hz respectively; a 13C-12C isotope shift of -17 ppb is also observed. Coupling constants for interhexagon (6:5) bonds range from 9.3-9.8 Hz, whilst those for interpentagon (6:6) bonds range from 13.9-1 6.3 Hz. The latter are exceptionally large, and the differentiation between the two types should prove a valuable aid in structure determination of hydrogenated fullerenes and derivatives thereof.

Fluorination of C60 at 550 degrees C leads to milligram quantities of two stable fullerene derivatives with 58-carbon cage structures: C58F18 and C58F17CF3. The compounds were characterized by mass spectrometry and fluorine nuclear magnetic resonance spectroscopy, and the data support a heptagonal ring in the framework. The resulting strain, which has hindered past attempts to prepare these smaller quasi-fullerenes, is mitigated here by hybridization change of some of the carbons in the pentagons from sp2 to sp3 because of fluorine addition. The loss of carbon from C60 is believed to occur via sequential fluorine addition to a CC single bond and an adjacent CC bond, followed by loss of a:CF2 carbene.

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