title: Formation and High Reactivity of the anti-Dioxo Form of High-Spin μ-Oxodioxodiiron(IV) as the Active Species That Cleaves Strong C-H Bonds.
abstract: Recently, it was shown that μ-oxo-μ-peroxodiiron(III) is converted to high-spin μ-oxodioxodiiron(IV) through O-O bond scission. Herein, the formation and high reactivity of the anti-dioxo form of high-spin μ-oxodioxodiiron(IV) as the active oxidant are demonstrated on the basis of resonance Raman and electronic-absorption spectral changes, detailed kinetic studies, DFT calculations, activation parameters, kinetic isotope effects (KIE), and catalytic oxidation of alkanes. Decay of μ-oxodioxodiiron(IV) was greatly accelerated on addition of substrate. The reactivity order of substrates is toluene<ethylbenzene≈cumene<trans-β-methylstyrene. The rate constants increased proportionally to the substrate concentration at low substrate concentration. At high substrate concentration, however, the rate constants converge to the same value regardless of the kind of substrate. This is explained by a two-step mechanism in which anti-μ-oxodioxodiiron(IV) is formed by syn-to-anti transformation of the syn-dioxo form and reacts with substrates as the oxidant. The anti-dioxo form is 620 times more reactive in the C-H bond cleavage of ethylbenzene than the most reactive diiron system reported so far. The KIE for the reaction with toluene/[D8 ]toluene is 95 at -30 °C, which the largest in diiron systems reported so far. The present diiron complex efficiently catalyzes the oxidation of various alkanes with H2 O2 .
authors.affiliation: Department of Molecular Chemistry and Biochemistry, Doshisha University, Tatara Miyakotani 1-3, Kyotanabe Kyoto, 610-0321, Japan. mkodera@mail.doshisha.ac.jp.
authors.forename: Masahito
authors.initials: M
authors.lastname: Kodera
authors.affiliation: Department of Molecular Chemistry and Biochemistry, Doshisha University, Tatara Miyakotani 1-3, Kyotanabe Kyoto, 610-0321, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Ishiga
authors.affiliation: Department of Molecular Chemistry and Biochemistry, Doshisha University, Tatara Miyakotani 1-3, Kyotanabe Kyoto, 610-0321, Japan.
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Tsuji
authors.affiliation: Department of Molecular Chemistry and Biochemistry, Doshisha University, Tatara Miyakotani 1-3, Kyotanabe Kyoto, 610-0321, Japan.
authors.forename: Katsutoshi
authors.initials: K
authors.lastname: Sakurai
authors.affiliation: Department of Molecular Chemistry and Biochemistry, Doshisha University, Tatara Miyakotani 1-3, Kyotanabe Kyoto, 610-0321, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Hitomi
authors.affiliation: Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, 819-0395, Japan.
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Shiota
authors.affiliation: Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, 819-0395, Japan.
authors.forename: P K
authors.initials: PK
authors.lastname: Sajith
authors.affiliation: Institute for Materials Chemistry and Engineering, Kyushu University, Fukuoka, 819-0395, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Yoshizawa
authors.affiliation: Department of Life Science, University of Hyogo, Kouto 2-1, Ako-gun Kamigori-cho Hyogo, 678-1297, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Mieda
authors.affiliation: Department of Life Science, University of Hyogo, Kouto 2-1, Ako-gun Kamigori-cho Hyogo, 678-1297, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ogura
keywords: C−H activation; iron; oxidation; oxido ligands; reaction mechanisms