Chemical Generation of C602- 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 = C 6 H 5 CH 2 and x = 1 for R = o -xylyl) by the reaction of C 60 2- with benzyl bromide or α,α‘-dibromo- o -xylene. Theoretical calculations predict that the 1,4-isomer of (C 6 H 5 CH 2 ) 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.