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

Abstract

Six-electron oxidation of anthracene to anthraquinone by a nonheme Mn -oxo complex, [(Bn-TPEN)Mn (O)] , proceeds through a rate-determining electron transfer from anthracene to [(Bn-TPEN)Mn (O)] , followed by subsequent fast oxidation reactions to give anthraquinone. The reduced Mn complex ([(Bn-TPEN)Mn ] ) is oxidized by [(Bn-TPEN)Mn (O)] rapidly to produce the μ-oxo dimer ([(Bn-TPEN)Mn -O-Mn (Bn-TPEN)] ). The oxygen atoms of the anthraquinone product were found to derive from the manganese-oxo species by the O-labelling experiments. In the presence of Sc ion, formation of an anthracene radical cation was directly detected in the electron transfer from anthracene to a Sc ion-bound Mn (O) complex, [(Bn-TPEN)Mn (O)-(Sc(OTf) ) ] , 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 (O)-(Sc(OTf) ) ] 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 (O)] and [(Bn-TPEN)Mn (O)-(Sc(OTf) ) ] was well-evaluated in light of the Marcus theory of electron transfer.

Oxidation of Naphthalene with a Manganese(IV) Bis(hydroxo) Complex in the Presence of Acid

“…It has been documented that the oxidation of polyaromatic compounds to quinones requires six electrons in total . Our mechanistic proposal for the oxidation of naphthalene with 2 is shown in Scheme .…”

“…[44,45] The mechanistic proposal for the oxidation of naphthalene by 2 is shown in Scheme 1. First, the rate-determining electron transfer from naphthalene to protonated 2 triggers the six-electron oxidation of naphthalene affording a naphthalene radical cation with [Mn III (TBDAP)(OH)(OH 2 )] 2+ (Scheme 1, pathway a ), followed by the further oxidations (Scheme 1, pathways b – f ).…”

The most reactive iron and manganese complexes with N-pentadentate ligands for dioxygen activation—synthesis, characteristics, applications

“…0 °C, time: ~ 50 min.) [ 86 ] [(Bn-TPEN)Mn IV = O] 2+ (0.5 mM)/CF 3 CH 2 OH /MeCN cyclohexene (0.2 M), cyclooctene (0.1 M) oxidation corresponding ketone, alcohol and/or epoxide; cyclohexenol (26%), cyclohexanone (8%), cyclohexene oxide (18%) and cyclooctene oxide (94%), respectively (temp. 25 °C) [ 81 ] *The highest conversions after 15 h, at 60 °C **Calculated on the basis of the introduced amounts of plastoquinone analogues, at 25 °C ***Calculated using the ratio of the final ClO 2 concentration to reacted chlorite concentration; for 4 mM [ClO 2 − ] 0 , at ambient temp ****Calculated on the basis of the introduced substrate concentration; for 1 mM catalyst in MeCN, 1 M substrate, after 24 h, under O 2 atmosphere, at ambient temp …”

Oxidation of Naphthalene with a Manganese(IV) Bis(hydroxo) Complex in the Presence of Acid

“…It has been documented that the oxidation of polyaromatic compounds to quinones requires six electrons in total. [44,45] Our mechanistic proposal for the oxidation of naphthalene with 2 is shown in Scheme 1. First, ratedetermining electron transfer from naphthalene to protonated 2 triggers six-electron oxidation of naphthalene,affording an aphthalene radical cation with [Mn III (TBDAP)(OH)-(OH 2 )] 2+ (Scheme 1, pathway a), which is followed by further oxidations (Scheme 1, steps b-f).…”

“…[44,45] Our mechanistic proposal for the oxidation of naphthalene with 2 is shown in Scheme 1. [44,45] Our mechanistic proposal for the oxidation of naphthalene with 2 is shown in Scheme 1.…”