Formation of hydrides of fullerene-C60 and fullerene-C70

Abstract

Fullerene-C₆₀ and fullerene-C₇₀ 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 ¹H NMR chemical shifts are highly solvent dependent, and are ca. 1 ppm further downfield in carbon disulfide than in benzene; the shifts for C₆₀H_n compounds are downfield compared with those for C₇₀H_n compounds, due possibly to differences in strain between the cages and/or a field effect operating across the cage void. 1,2,3,4-Tetrahydrofullerene-C₆₀ is the main product from reduction of fullerene-C₆₀ 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-C₇₀; two have been characterised as 1,5,6,9-tetrahydrofullerene-C₇₀ and 1,7,8,9-tetrahydrofullerene-C₇₀, 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 1,2-dihydrofullerene-60 in the ¹H 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 13.9–16.3 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.