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 C(76)Me(2)(one of C(s) symmetry due to 1,6-C(76)Me(2)) and C(76)(CH(2))(n)(n= 2-4), together with corresponding mono-oxides. The single line (1)H NMR spectrum of mono-oxide C(76)Me(2)O 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 C(76)Me(4)O(2) is the first bis oxahomo[76]fullerene to be isolated and gives two equal-intensity lines in the (1)H 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 C(84)Me(2) derivatives were isolated, two of them in quantities sufficient to show the symmetries as C(1), and either C(2) or C(s).