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

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 C-76(CH2)(n) (n = 2-4), together with corresponding mono-oxides. The single line H-1 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-C(76)Me(2)giving a product of C-2 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 H-1 NMR spectrum showing that it must also have C-2 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 C-1, and either C-2 or C-s.