Redox Reaction of Benzyl Radicals with Aromatic Radical Ions Photogenerated. The Marcus Inverted Region and the Selective Formation of Carbocations or Carbanions

Efficient redox reactions of benzyl-type radicals were achieved by irradiating an aromatic donor/acceptor pair with substituted dibenzyl ketones as a radical precursor in MeOH−MeCN. In this system, the aromatic radical ion pair was generated by photoinduced electron transfer followed by one-electron oxidation and reduction of photogenerated benzyl radicals (R•) by the radical ions to afford benzyl cations (R+) and anions (R-). The cations and anions were trapped by MeOH to yield ROMe and RH, respectively. The relative product ratios were determined for a variety of donor−acceptor pairs, reflecting the relative efficiencies of the redox reaction of benzyl radicals with a steady-state concentration of radical ions. The selective formation of carbocations or carbanions was achieved in some sets of donor/acceptor pairs. Assuming that the radical ions exist in a 1:1 ratio in the steady state, the product ratios are equal to the relative electron transfer rates, which are analyzed in terms of the free energy ch...