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

Abstract

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 C₇₀H_36/38. 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 C₇₀H_36/38 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.