Multi-Electron Oxidation of Anthracene Derivatives by Nonheme Manganese(IV)-Oxo Complexes

摘要

Six-electron oxidation of anthracene to anthraquinone by a nonheme Mn~(IV)-oxo complex, [(Bn-TPEN)Mn~(IV)(O)]~(2+) , proceeds through a rate-determining electron transfer from anthracene to [(Bn-TPEN)Mn~(IV)(O)]~(2+), followed by subsequent fast oxidation reactions to give anthraquinone. The reduced MnII complex ([(Bn-TPEN)MnII]~(2+)) is oxidized by [(Bn-TPEN)- Mn~(IV)(O)]~(2+) rapidly to produce the μ-oxo dimer ([(Bn-TPEN)- MnIII-O-MnIII(Bn-TPEN)]4+). The oxygen atoms of the anthraquinone product were found to derive from the manganeseoxo species by the ~(18)O-labelling experiments. In the presence of Sc~(3+) ion, formation of an anthracene radical cation was directly detected in the electron transfer from anthracene to a Sc~(3+) ion-bound Mn~(IV)(O) complex, [(Bn-TPEN)- Mn~(IV)(O)-(Sc(OTf)_3)_2]~(2+), followed by subsequent further oxidation to yield anthraquinone. When anthracene was replaced by 9,10-dimethylanthracene, electron transfer from 9,10-dimethylanthracene to [(Bn-TPEN)Mn~(IV)(O)-(Sc(OTf)_3)_2]~(2+) occurred rapidly to produce stable 9,10-dimethylanthracene radical cation. The driving force dependence of the rate constants of electron transfer from the anthracene derivatives to [(Bn-TPEN)Mn~(IV)(O)]~(2+) and [(Bn-TPEN)Mn~(IV)(O)-(Sc(OTf)_3)_2]~(2+) was well-evaluated in light of the Marcus theory of electron transfer.