The chemistry of metal-superoxo intermediates started being unveiled in oxidation reactions by enzymes and their synthetic model compounds. However, aromatic hydroxylation reactions by the metal-superoxo species are yet to be demonstrated. In this study, we report for the first time that the hydroxylation of aromatic compounds such as anthracene and its derivatives by a mononuclear nonheme Cr(iii)-superoxo complex, [(Cl)(TMC)CrIII(O2)]+ (1), occurs in the presence of triflic acid (HOTf) via the rate-determining proton-coupled electron transfer (PCET) from anthracene to 1, followed by a fast further oxidation to give anthraquinone. The rate constants of electron transfer from anthracene derivatives to 1 in the presence of HOTf are well analyzed in light of the Marcus theory of electron transfer.
Bibliographical noteFunding Information:
This work was supported by a SENTAN project from the Japan Science and Technology Agency (JST) to S. F. and JSPS KAKENHI (No. 16H02268 to S. F.) from MEXT, Japan, and the NRF of Korea through CRI (NRF-2012R1A3A2048842 toW. N.), GRL (NRF-2010- 00353 to W. N.), and the Basic Science Research Program (2017- R1D1A1B03029982 to Y.-M. L. and 2017R1D1A1B03032615 to S. F.).
© 2019 The Royal Society of Chemistry.