Mechanistic Studies of Catalytic O<sub>2</sub>-to-H<sub>2</sub>O<sub>2</sub> Conversion at a Single Cobalt Site
Tao Liu, Meng Jia, Haonan Qin, Mengchun Zhang, Ning Sun, Benxing Mei, Huamin Li, Xuepeng Zhang, Jun Li, Rui Cao
Abstract
Understanding oxygen reduction reaction (ORR) mechanisms is of fundamental significance. Although metal hydrosuperoxos and metal hydroperoxos are considered to be key intermediates in ORR, these two species as well as their reaction natures are poorly understood because they are highly active with various reaction pathways. Herein, we report on the mechanistic studies of the ORR with Co II porphyrin 1 . Complex 1 is selective for catalytic O 2 -to-H 2 O 2 conversion with decamethylferrocene as the reductant and HClO 4 as the proton source. By employing the molecular pocket of 1 to stabilize the O 2 -adducts, we characterized Co III -hydrosuperoxo, [Co III (O 2 • H)] +, and Co III -hydroperoxo, [Co III (O 2 H)], studied the one-electron reduction of [Co III (O 2 • H)] + to generate [Co III (O 2 H)], and revealed a proton transfer–electron transfer (PTET) pathway for [Co III (O 2 H)] to generate Co II and H 2 O 2 . This work is therefore significant to confirm the key role of [Co III (O 2 • H)] + and [Co III (O 2 H)] in the catalytic ORR cycle and to establish a PTET pathway of [Co III (O 2 H)] to give H 2 O 2 .