Oxidation of Reduced Keggin Heteropolytungstates by Dioxygen in Water Catalyzed by Cu(II)

Mooeung Kim, Ira A. Weinstock, Yurii V. Geletii, Craig L. Hill

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

The reaction of reduced polyoxometalates (POMs) with dioxygen is centrally important in POM catalysis. We report that this process, as represented by the one-electron-reduced Keggin complexes POMred (α-AlW12O406-, α-SiW12O405-, and α-PW12O404-), is efficiently catalyzed by copper complexes. The Cu-catalyzed pathway is dominant in the presence of as low as ∼0.1 μM of Cu, a copper concentration that is typically lower than the copper ion contamination in aqueous solutions. The reaction kinetics and mechanism have been comprehensively studied in sodium sulfate buffer at pH 2.0. The catalytic pathway includes a reversible reduction of Cu(II) by POMred, followed by a fast reoxidation of Cu(I) by O2 to regenerate Cu(II). The rate constants of the first catalytic steps were determined by three approaches and found to be (1.8 ± 0.3) × 105 and 57 ± 15 M-1 s-1 for SiW12O405- and PW12O404-, respectively. These reactions are thermodynamically more favorable and therefore proceed significantly more quickly than those for the direct outer-sphere electron transfer to O2. The proposed reaction mechanism quantitatively describes the experimental kinetic curves over a wide range of experimental conditions.

Original languageEnglish
Pages (from-to)7048-7054
Number of pages7
JournalACS Catalysis
Volume5
Issue number12
DOIs
StatePublished - 20 Oct 2015

Keywords

  • catalytic oxidation
  • oxidation by dioxygen
  • reaction mechanism
  • reduced Keggin polyoxometalates
  • submicromolar copper catalysis

Fingerprint

Dive into the research topics of 'Oxidation of Reduced Keggin Heteropolytungstates by Dioxygen in Water Catalyzed by Cu(II)'. Together they form a unique fingerprint.

Cite this