title: 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.
abstract: 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 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.
authors.affiliation: Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743, Korea.
authors.forename: Young Joo
authors.initials: YJ
authors.lastname: Song
authors.forename: Min Young
authors.initials: MY
authors.lastname: Hyun
authors.forename: Jun Ho
authors.initials: JH
authors.lastname: Lee
authors.forename: Hong Gyu
authors.initials: HG
authors.lastname: Lee
authors.forename: Jin Hoon
authors.initials: JH
authors.lastname: Kim
authors.forename: Seung Pyo
authors.initials: SP
authors.lastname: Jang
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Noh
authors.forename: Youngmee
authors.initials: Y
authors.lastname: Kim
authors.forename: Sung-Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Suk Joong
authors.initials: SJ
authors.lastname: Lee
authors.forename: Cheal
authors.initials: C
authors.lastname: Kim
mesh_terms: D000588:Amines / Q000737:chemistry*; D001713:Biphenyl Compounds / Q000737:chemistry*; D002384:Catalysis; D003035:Cobalt / Q000737:chemistry*; D020650:Combinatorial Chemistry Techniques; D003500:Cyclization; D007093:Imidazoles / Q000737:chemistry*; D015394:Molecular Structure; D016877:Oxidants / Q000737:chemistry*; D013237:Stereoisomerism; D014230:Triazoles / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000588:Amines; D001713:Biphenyl Compounds; D007093:Imidazoles; D016877:Oxidants; D014230:Triazoles; D003035:Cobalt