Chemical generation of C-60(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 C-60(.-) or C-60(2-) is described. The electron transfer reduction of C-60 by Q(2-) occurs via stepwise electron transfer from the Q(2-) to C-60 in acetonitrile or benzonitrile. The C-60(2-) thus generated is used as the starting material in the synthesis of R(x)C(60) (where x = 2 for R = C6H5CH2 and x = 1 for R = o-xylyl) by the reaction of C-60(2-) with benzyl bromide or alpha,alpha'-dibromo-o-xylene. Theoretical calculations predict that the 1,4-isomer of (C6H5CH2)(2)C-60 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 C-60 as well as the subsequent reactions between C-60(2-) and the alkyl bromides. The comparison of the observed rate constants of the reactions of C-60(2-) with those of electron transfer from tetramethylsemiquinone radical anion to the same alkyl bromide indicates that the formation of R(x)C(60) proceeds via the rate-determining electron transfer from C-60(2-) to the alkyl bromide.