Methylation of [76]fullerene and [84]fullerenes; the first oxahomo derivatives of a higher fullerene

Abstract

Methylation of [76]fullerene by reaction with Al–Ni alloy/NaOH followed by quenching of the intermediate anions with methyl iodide gives a mixture of methylated and methylenated products together with oxide derivatives. The major derivatives are five isomers of C₇₆Me₂ (one of C_s symmetry due to 1,6-C₇₆Me₂) and C₇₆(CH₂)_n (n = 2–4), together with corresponding mono-oxides. The single line ¹H NMR spectrum of mono-oxide C₇₆Me₂O shows it is an oxahomofullerene (ether) the first example derived from [76]fullerene, oxygen being inserted between the CMe groups in 1,6-C₇₆Me₂giving a product of C₂ symmetry. The probable structures of the unsymmetrical dimethyl derivatives have been deduced from heats of formation calculated by AM1 and density functional methods. Bis-oxide C₇₆Me₄O₂ is the first bis oxahomo[76]fullerene to be isolated and gives two equal-intensity lines in the ¹H NMR spectrum showing that it must also have C₂ symmetry; probable structures are considered. Methylation of [84]fullerene takes place less readily and only four C₈₄Me₂ derivatives were isolated, two of them in quantities sufficient to show the symmetries as C₁, and either C₂ or C_s.