A functional phenoxazinone synthase model based on dioximatomanganese(II). Kinetics and mechanism of the catalytic oxidation of 2-aminophenols by dioxygen

Imola Cs Szigyártó, Tatiana M. Simándi, László I. Simándi, László Korecz, Nóra Nagy

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

The dimeric dioximatomanganese(II) complex [Mn2(HL)2](BPh4)2 (1) (where H2L is [HON{double bond, long}C(CH3)C(CH3){double bond, long}NCH2CH2]2NH) dissociates to the monomer [Mn(HL)]+ (2) upon dissolution in MeOH. Complex 2 is a functional phenoxazinone synthase model catalyzing the base-assisted oxidative dimerization of 2-aminophenol (H3ap) to 2-amino-3H-phenoxazine-3-one (apx) by dioxygen under ambient conditions via an o-benzoquinone monoimine (bqmi) intermediate, which, however, cannot be directly detected due to its high reactivity. If H3ap is replaced by 2-anilino-4,6-di-tert-butylphenol (3), a structural analog where the required positions are blocked, oxidation occurs without dimerization, affording the corresponding N-substituted o-quinone monoimine. Free radical intermediates were detected by ESR spectroscopy in both reactions. The kinetics of the catalytic oxidation of H3ap was studied spectrophotometrically and the corresponding rate equation established. It is consistent with a mechanism involving the formation of a catalyst-H2apO2 ternary complex, which decomposes in the rate-determining step, generating a semiquinone monoimine undergoing noncatalytic oxidative dimerization to apx.

Original languageEnglish
Pages (from-to)270-276
Number of pages7
JournalJournal of Molecular Catalysis A: Chemical
Volume251
Issue number1-2
DOIs
Publication statusPublished - May 17 2006

Keywords

  • 2-Aminophenol
  • 2-Anilino-4,6-di-tert-butylphenol
  • ESR spectroscopy
  • Functional models
  • Phenoxazinone synthase
  • Semiquinone monoimine

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology
  • Physical and Theoretical Chemistry

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