Chemical Generation of C₆₀^2- and Electron Transfer Mechanism for the Reactions with Alkyl Bromides

Abstract

A simple solution-phase method that uses chemically generated p-benzoquinone dianions (Q2-) as the reductant in the selective generation of either C60•- or C602- is described. The electron transfer reduction of C60 by Q2- occurs via stepwise electron transfer from the Q2- to C60 in acetonitrile or benzonitrile. The C602- thus generated is used as the starting material in the synthesis of RxC60 (where x = 2 for R = C6H5CH2 and x = 1 for R = o-xylyl) by the reaction of C602- 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 Q2- to C60 as well as the subsequent reactions between C602- and the alkyl bromides. The comparison of the observed rate constants of the reactions of C602- with those of electron transfer from tetramethylsemiquinone radical anion to the same alkyl bromide indicates that the formation of RxC60 proceeds via the rate-determining electron transfer from C602- to the alkyl bromide.