Aliphatic C-H bond activation initiated by a (μ-η2: η2-peroxo)dicopper(II) complex in comparison with cumylperoxyl radical

Takahiro Matsumoto, Kei Ohkubo, Kaoru Honda, Akiko Yazawa, Hideki Furutachi, Shuhei Fujinami, Shunichi Fukuzumi, Masatatsu Suzuki

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Abstract

A (μ-η22-peroxo)dicopper(II) complex, [Cu2(H-L)(O2)]2+ (1-O2), supported by the dinucleating ligand 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl] benzene (H-L) is capable of initiating C-H bond activation of a variety of external aliphatic substrates (SHn): 10-methyl-9,10-dihydroacridine (AcrH2), 1,4-cyclohexadiene (1,4-CHD), 9,10-dihydroanthracene (9,10-DHA), fluorene, tetralin, toluene, and tetrahydrofuran (THF), which have C-H bond dissociation energies (BDEs) ranging from ∼75 kcal mol-1 for 1,4-CHD to ∼92 kcal mol-1 for THF. Oxidation of SH n afforded a variety of oxidation products, such as dehydrogenation products (SH(n-2)), hydroxylated and further-oxidized products (SH(n-1)OH and SH(n-2)=O), dimers formed by coupling between substrates (H(n-1)S-SH(n-1)) and between substrate and H-L (H-L-SH(n-1)). Kinetic studies of the oxidation of the substrates initiated by 1-O2 in acetone at -70°C revealed that there is a linear correlation between the logarithms of the rate constants for oxidation of the C-H bonds of the substrates and their BDEs, except for THF. The combination of this correlation and the relatively large deuterium kinetic isotope effects (KIEs), k2H/k2D (13 for 9,10-DHA, ≳29 for toluene, and ∼34 for THF at -70°C and ∼9 for AcrH2 at -94°C) indicates that H-atom transfer (HAT) from SHn (SDn) is the rate-determining step. Kinetic studies of the oxidation of SHn by cumylperoxyl radical showed a correlation similar to that observed for 1-O2, indicating that the reactivity of 1-O2 is similar to that of cumylperoxyl radical. Thus, 1-O 2 is capable of initiating a wide range of oxidation reactions, including oxidation of aliphatic C-H bonds having BDEs from ∼75 to ∼92 kcal mol-1, hydroxylation of the m-xylyl linker of H-L, and epoxidation of styrene (Matsumoto, T.; et al. J. Am. Chem. Soc. 2006, 128, 3874).

Original languageEnglish
Pages (from-to)9258-9267
Number of pages10
JournalJournal of the American Chemical Society
Volume131
Issue number26
DOIs
StatePublished - 8 Jul 2009

Bibliographical note

Funding Information:
We are grateful to the New Zealand Dairy Research Institute for funding most of this work. We also acknowledge financial assistance from the Foundation for Research, Science and Technology, under contract CO 1801. Theco-operation andhelp ofthe farmers of the Toenepi catchment, and their families is gratefully acknowledged. Our colleagues at AgResearch, NIWA and NZDRI provided useful comments andconstructive criticism.

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