期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 18, 期 19, 页码 6094-6101出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201103916
关键词
catalysts; cleavage reactions; cobalt; epoxidation; high-valent species
资金
- Korean Science & Engineering Foundation [2009 0074066]
- Converging Research Center through the National Research Foundation of Korea (NRF)
- Ministry of Education, Science and Technology [2011K000675]
- National Research Foundation of Korea [2009-0074066] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl2][Et4N] (1; H2bpc=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 CoIII 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 CoV?O (3) and CoIV?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 CoV?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 CoV?O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.
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