Hydrogenation of [76]-, [78]- and [84]-fullerenes: Cage degradation

The title fullerenes have been reduced under conditions (Zn, cone. HCl, toluene solution, 1 h, N-2, dark, room temp.) that give C60H36 from [60]fullerene and C70H36-40 from [70]fullerene. Reduction of [76]fullerene gives C76H46-50' [78]fullerene gives a broader spectrum of reduction products (consistent with the diverse isomeric composition of the parent fullerene), the most abundant species being C78H36 and C78H48 (main component), and [84]fullerene yields mainly CH84H48-52. In each case, reduction of the higher fullerenes is accompanied by cage breakdown to C60H36 and C70H36-40, the relative proportions of which vary with the starting fullerene. Thus reduction of [76]fullerene gave only a trace of C70H36-40, whereas [78]fullerene gave considerably more. Reduction of [84]fullerene over an extended period (5 h) resulted in complete degradation to C60H36. HPLC separation of the hydrogenated fullerenes on a Cosmosil column (toluene eluent), showed them to elute more rapidly the larger the cage, as found previously for C60H36 and C70H36-40. By contrast, on the same column and under the same conditions, the parent fullerenes elute more slowly the higher the molecular weight.