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

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 Mn II complex ([(Bn‐TPEN)Mn II ] 2+ ) is oxidized by [(Bn‐TPEN)Mn IV (O)] 2+ rapidly to produce the μ‐oxo dimer ([(Bn‐TPEN)Mn III ‐O‐Mn III (Bn‐TPEN)] 4+ ). The oxygen atoms of the anthraquinone product were found to derive from the manganese‐oxo 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.