Manganese-salen complexes as oxygen-transfer agents in catalytic epoxidations - A density functional study of mechanistic aspects

Luigi Cavallo, Heiko Jacobsen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

73 Scopus citations

Abstract

The mechanism of the Jacobsen-Katsuki epoxidation has been investigated by application of density functional theory; the results of a series of calculations for simplified model systems of different spin states are presented. In the chosen computational approach, the epoxidation of ethylene with a cationic five-coordinate model catalyst is predicted to occur through a radical intermediate, similarly to the reaction mechanism calculated for the corresponding neutral six-coordinate species. Although the radical intermediate shows a small energetic preference for the quintet state over the triplet state, the computed reaction profile does not suggest that two-state reactivity involving spin change plays a major role during the oxygen-transfer step. Comparative orbital analysis of the cationic and the neutral complexes elucidates the role of a ligand trans to the oxo group. A π-donor trans to the forming OR- ligand in the radical intermediate causes a relative destabilization of a possible quintet occupation, thus conferring spin rigidity to the six-coordinate species derived from the neutral catalyst. A reaction pathway resulting in rotational collapse might involve a spin-crossing process. The ligand framework of the tetra-chelating N,O ligand in the radical intermediate exhibits a considerable amount of ligand folding.

Original languageEnglish (US)
Pages (from-to)892-902
Number of pages11
JournalEuropean Journal of Inorganic Chemistry
Issue number5
DOIs
StatePublished - Jan 1 2003

Keywords

  • Density functional calculations
  • Epoxidation
  • Manganese
  • N,O ligands
  • Radicals

ASJC Scopus subject areas

  • Inorganic Chemistry

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