Chemical generation of C₆₀^2- and electron transfer mechanism for the reactions with alkyl bromides

A simple solution-phase method that uses chemically generated p-benzoquinone dianions (Q^2-) as the reductant in the selective generation of either C₆₀^•- or C₆₀^2- is described. The electron transfer reduction of C₆₀ by Q^2- occurs via stepwise electron transfer from the Q^2- to C₆₀ in acetonitrile or benzonitrile. The C₆₀^2- thus generated is used as the starting material in the synthesis of R_xC₆₀ (where x = 2 for R = C₆H₅CH₂ and x = 1 for R = o-xylyl) by the reaction of C₆₀^2- with benzyl bromide or α,α′-dibromo-o-xylene. Theoretical calculations predict that the 1,4-isomer of (C₆H₅CH₂)₂C₆₀ should be selectively formed, and this is confirmed by single-crystal X-ray diffraction studies. UV-visible and near-IR spectroscopy were used to monitor the progress of electron transfer from the Q^2- to C₆₀ as well as the subsequent reactions between C₆₀^2- and the alkyl bromides. The comparison of the observed rate constants of the reactions of C₆₀^2- with those of electron transfer from tetramethylsemiquinone radical anion to the same alkyl bromide indicates that the formation of R_xC₆₀ proceeds via the rate-determining electron transfer from C₆₀^2- to the alkyl bromide.