Methylation of [70]fullerene

Abstract

Methylation of [70]fullerene by different methods yields products indicative of two reduction manifolds. One involves addition principally at the polar region, the other involves addition around the equator, this diverse behaviour paralleling that found previously in hydrogenation; different steric requirements of the reagents are probably responsible. Methylation by reduction with Al–Ni alloy–NaOH–dioxane–THF followed by reaction with MeI gives C₇₀Me_n (n = 2, 4, 6, 8, 10) (equatorial addition). These products are isostructural with the corresponding C₇₀Ph_n species despite being formed via a different reaction type (the eight-fold addend being also the most abundant in each reaction), indicating that a fundamental property governs [70]fullerene addition. Methylation by reaction with lithium followed by quenching with methyl iodide gives C₇₀Me_n containing up to twenty-six methyl groups, C₇₀Me₆ being the most abundant species. The isolated C₇₀Me₂ consists mainly of a 3.4 ∶ 1 ratio of the 1,2- and 5,6-isomers (polar addition), together with smaller amounts of five other unsymmetrical isomers. One of these latter (together with a further isomer) is produced from nucleophilic substitution of C₇₀Cl₁₀ by MeLi which also gives C₇₀Me_n (n = 4, 6, 8) as mixtures of uncharacterised isomers in low yields. Like their phenylated counterparts, both C₇₀Me₈ and C₇₀Me₁₀ are fluorescent; C₇₀Me₈ forms a tetra-oxide on standing in air and light as does C₇₀Ph₈.