Poster Presentation 21st International Conference on Biological Inorganic Chemistry 2025

H2O2 Activation and Alkane Oxidation by Mono-copper Complex with R-dpa Tridentate Ligand: Complex-based Active Species is a Key Feature in the Efficient Substrate Oxidation (#473)

kyosuke Fujikawa 1 , Seigfried Schindler 2 , Hiroaki Kitagishi 1 , Masahito Kodera 1
  1. Doshisha University, Miyamaki, Kyotanabe-shi, Kyoto, Japan
  2. Institute of Inorganic and analytical Chemistry, Justus Liebig University Giessen, Geissen, Land Hessen, Germany

C-H activation of methane is one of the most challenging reactions due to difficulty of the oxidation. In nature, however, methane monooxygenases (MMO) catalyze the reaction under ambient conditions. Yoshizawa et al. proposed that particulate methane monooxygenases (pMMO) form [CuII2(μ-OH)(μ-O•)] as the active species to show high oxidation ability of the strong C-H bond of methane on the DFT studies.[1]  It, however, has not been detected at all, and no chemical evidence of the active species of pMMO has not been reported. Thus, detailed mechanistic studies of alkane oxidation with H2O2 catalyzed by various copper complexes may give some insights into understanding the active species in the H2O2 activation and the C-H oxidation.

So far, H2O2 activation by Cu(II) complexes with tetradentate ligand has been well studied.[2] It is known that Cu(II) complex with tris(pycolyl)amine (tpa) activates H2O2 via Fenton-type reaction, in which HO• is generated as active species.[3]

Masuda et al. reported that Cu(II) complex with N-tert-butyl-di(pycolyl)amine (tert-Budpa) formed CuII-OOH species upon reaction with H2O2.[4] On the other hand, Itoh showed that Cu(I) complex with N-phenethyl-di(pycolyl)amine (Phedpa) forms bis-μ-oxodicopper(III) complex [CuIII2(µ-O)2]2+ upon reaction with O2 which can oxidize the C-H bond intramolecularly.[5]

 In this study, we studied the H2O2 activation and C-H oxidation of Cu(II) complexes with N-alkyl-di(pycolyl)amine (Rdpa, R = Me, Phe, tert-Bu), [Cu(Rdpa)](ClO4)2 (1R). Fenton-type reaction mainly occurred in the reaction of 1t-Bu and partly of 1Me, and in both reactions, HO• formed non-selectively oxidized catalysts to shorten catalyst life. Interestingly, 1Phe was not the case and gave long catalyst life. These results suggested that 1Phe mainly forms the complex-based active species and the Fenton-type reaction is a minor reaction. Here, we carried out the low temperature stopped-flow experiments to examine reaction intermediates in the H2O2 activation by 1R. Moreover, detailed reactivity studies for the cyclohexane oxidation with H2O2 catalyzed by 1R revealed that the Fenton type reaction and the formation of the complex-based active species were controlled by the alkyl substituents of Rdpa.

  1. [1] K. Yoshizawa, et. al., Inorg. Chem. 2013, 52, 7907−7917. [2] I. Garcia-Bosch, M. A. Siegler, Angew. Chem., Int. Ed. 2016, 55, 12873-12876. [3] K. D. Karlin, et al., J. Am. Chem. Soc. 2015, 137, 2867−2874. [4] H. Masuda, et al., Chem. Comm., 2003, 2700–2701. [5] S. Itoh, et al., Inorg. Chem., 2003, 42(24), 8087-8097