title: Synthesis, Characterization, and Catalytic Activities of A Nickel(II) Monoamido-Tetradentate Complex: Evidence For NiIII-Oxo and NiIV-Oxo Species.
abstract: A new mononuclear nickel(II) complex, [NiII(dpaq)Cl] (1), containing a tetradentate monoamido ligand, dpaq (dpaq=2-[bis(pyridin-2-ylmethyl)amino]-N-(quinolin-8-yl)acetamide), has been synthesized and characterized by IR spectroscopy, elemental analysis, and UV/Vis spectroscopy. The structure of the nickel complex has been determined by X-ray crystallography. This nonheme NiIIcomplex 1 catalyzed the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (m-CPBA) under mild conditions. Olefin epoxidation using this catalytic system has been proposed to involve a new reactive NiIV-oxo (4) species, based on the evidence from a PPAA (peroxyphenylacetic acid) probe, Hammett studies, H218O exchange experiments, and ESI mass spectroscopic analysis. Moreover, the nature of solvent significantly influenced partitioning between heterolytic and homolytic O-O bond cleavage of the Ni-acylperoxo intermediate (2). The O-O bond of 2 proceeded predominantly through heterolytic cleavage in a protic solvent, such as CH3OH. These results suggest that possibly a NiIV-oxo species is a common reactive intermediate in protic solvents. The two active oxidants, namely NiIV-oxo (3) and NiIII-oxo (4), which are responsible for stereospecific olefin epoxidation and radical-type oxidations, respectively, operate in aprotic solvents.
authors.affiliation: Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul, 139-743, Korea.
authors.forename: Kwon Hee
authors.initials: KH
authors.lastname: Bok
authors.affiliation: Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul, 139-743, Korea.
authors.forename: Myoung Mi
authors.initials: MM
authors.lastname: Lee
authors.affiliation: Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul, 139-743, Korea.
authors.forename: Ga Rim
authors.initials: GR
authors.lastname: You
authors.affiliation: Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul, 139-743, Korea.
authors.forename: Hye Mi
authors.initials: HM
authors.lastname: Ahn
authors.affiliation: Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul, 139-743, Korea.
authors.forename: Ka Young
authors.initials: KY
authors.lastname: Ryu
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 120-750, Korea.
authors.forename: Sung-Jin
authors.initials: SJ
authors.lastname: Kim
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul, 120-750, Korea.
authors.forename: Youngmee
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Department of Fine Chemistry, Seoul National University of Science and Technology, Seoul, 139-743, Korea.
authors.forename: Cheal
authors.initials: C
authors.lastname: Kim
keywords: epoxidation; nickel; nickel-oxo species; olefins; oxidation