Amide-based nonheme cobalt(III) olefin epoxidation catalyst: Partition of multiple active oxidants Co V=O, Co IV=O, and Co III-OO(O)CR

Young Joo Song, Min Young Hyun, Jun Ho Lee, Hong Gyu Lee, Jin Hoon Kim, Seung Pyo Jang, Jin Young Noh, Youngmee Kim, Sung Jin Kim, Suk Joong Lee, Cheal Kim

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Abstract

A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl 2][Et 4N] (1; H 2bpc=4,5-dichloro-1,2-bis(2-pyridine-2- carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X-ray crystallography. This nonheme Co III complex catalyzes olefin epoxidation upon treatment with meta-chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an O-O bond to afford Co V=O (3) and Co IV=O (4) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical-type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the Co-OOC(O)R (2) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the O-O bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the O-O bond of the Co-OOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete Co V=O intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible Co V=O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.

Original languageEnglish
Pages (from-to)6094-6101
Number of pages8
JournalChemistry - A European Journal
Volume18
Issue number19
DOIs
Publication statusPublished - 2012 May 7

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Keywords

  • catalysts
  • cleavage reactions
  • cobalt
  • epoxidation
  • high-valent species

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Song, Y. J., Hyun, M. Y., Lee, J. H., Lee, H. G., Kim, J. H., Jang, S. P., Noh, J. Y., Kim, Y., Kim, S. J., Lee, S. J., & Kim, C. (2012). Amide-based nonheme cobalt(III) olefin epoxidation catalyst: Partition of multiple active oxidants Co V=O, Co IV=O, and Co III-OO(O)CR. Chemistry - A European Journal, 18(19), 6094-6101. https://doi.org/10.1002/chem.201103916