Activity of peroxo and hydroperoxo complexes of Ti(IV) in olefin epoxidation: A density functional model study of energetics and mechanism

Ilya V. Yudanov, Philip Gisdakis, Cristiana Di Valentin, Notker Rösch

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75 Scopus citations

Abstract

Epoxidation of olefins by Ti(IV) peroxo and hydroperoxo (alkylperoxo) complexes was investigated using a hybrid DFT method (B3LYP). Reaction energies and activation barriers for direct oxygen transfer to ethylene as a model olefin were computed for various model complexes to compare the epoxidation activity of Ti(η2-O2) and TiOOR (R = H, CH3) moieties. The activity of complexes with a Ti(O2) peroxo group is shown to be essentially quenched when the coordination sphere of the complex is saturated by strongly basic (σ-donor) ligands. In contrast, the activity of a TiOOH functional group depends only weakly on the saturation of the coordination sphere of the Ti center. Substitution of methyl for hydrogen in a TiOOH group is found to slightly increase the activation barrier of epoxidation. The computational results give preference to reaction paths that involve TiOOR species. The factors governing the activity of Ti(O2) and TiOOR groups, in particular the effects of donor ligands, are discussed on the basis of a molecular orbital analysis.

Original languageEnglish
Pages (from-to)2135-2145
Number of pages11
JournalEuropean Journal of Inorganic Chemistry
Issue number12
DOIs
StatePublished - 1999

Keywords

  • Density functional calculations
  • Epoxidation
  • Peroxo complexes
  • Titanium
  • Transition states

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