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

Abstract

The title fullerenes have been reduced under conditions (Zn, conc. HCl, toluene solution, 1h, N₂, dark, room temp.) that give C₆₀H₃₆ from [60]fullerene and C₇₀H_36–40 from [70]fullerene. Reduction of [76]fullerene gives C₇₆H_46–50, [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 C₈₄H_48–52. In each case, reduction of the higher fullerenes is accompanied by cage breakdown to C₆₀H₃₆ and C₇₀H_36–40 the relative proportions of which vary with the starting fullerene. Thus reduction of [76]fullerene gave only a trace of C₇₀H_30–40, whereas [78]fullerene gave considerably more. Reduction of [84]fullerene over an extended period (5h) 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 C₇₀H_36–40. By contrast, on the same column and under the same conditions, the parent fullerenes elute more slowly the higher the molecular weight.