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

A (μ-η²:η²-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 (SH_n): 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), k₂^H/k₂^D (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 SH_n (SD_n) is the rate-determining step. Kinetic studies of the oxidation of SH_n 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).