Lewis versus Bronsted Acid Activation of a Mn(IV) Catalyst for Alkene Oxidation

Jorn D. Steen, Stepan Stepanovic, Mahsa Parvizian, Johannes W. de Boer, Ronald Hage, Juan Chen, Marcel Swart, Maja Gruden, Wesley R. Browne*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

Lewis acid (LA) activation by coordination to metal oxido species has emerged as a new strategy in catalytic oxidations. Despite the many reports of enhancement of performance in oxidation catalysis, direct evidence for LA-catalyst interactions under catalytically relevant conditions is lacking. Here, we show, using the oxidation of alkenes with H2O2 and the catalyst [Mn-2(mu-O)(3)(tmtacn)(2)](PF6)(2) (1), that Lewis acids commonly used to enhance catalytic activity, e.g., Sc(OTf)(3), in fact undergo hydrolysis with adventitious water to release a strong Bronsted acid. The formation of Bronsted acids in situ is demonstrated using a combination of resonance Raman, UV/vis absorption spectroscopy, cyclic voltammetry, isotope labeling, and DFT calculations. The involvement of Bronsted acids in LA enhanced systems shown here holds implications for the conclusions reached in regard to the relevance of direct LA-metal oxido interactions under catalytic conditions.

Original languageEnglish
Pages (from-to)14924-14930
Number of pages7
JournalInorganic Chemistry
Volume58
Issue number21
DOIs
Publication statusPublished - 4-Nov-2019

Keywords

  • INACTIVE METAL-IONS
  • COUPLED ELECTRON-TRANSFER
  • CRYSTAL-STRUCTURE
  • OXYGEN-TRANSFER
  • DIOXYGEN ACTIVATION
  • MANGANESE COMPLEXES
  • CIS-DIHYDROXYLATION
  • ATOM TRANSFER
  • TRIFLIC ACID
  • REACTIVITY

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