Premium
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
Author(s) -
Song Young Joo,
Hyun Min Young,
Lee Jun Ho,
Lee Hong Gyu,
Kim Jin Hoon,
Jang Seung Pyo,
Noh Jin Young,
Kim Youngmee,
Kim SungJin,
Lee Suk Joong,
Kim Cheal
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201103916
Subject(s) - heterolysis , chemistry , homolysis , cobalt , medicinal chemistry , ligand (biochemistry) , olefin fiber , deprotonation , bond cleavage , moiety , amide , catalysis , stereochemistry , electron paramagnetic resonance , radical , organic chemistry , ion , biochemistry , receptor , physics , nuclear magnetic resonance
A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl 2 ][Et 4 N] ( 1 ; H 2 bpc=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 OO 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 CoOOC(O)R ( 2 ) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the OO bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the OO bond of the CoOOC(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.