Theoretical perspective on C-H/O-H activation by Cu-O in biological and synthetic systems

Dioxygen activations constitute one of core issues in copper-dependent metalloenzymes. Upon O2 activation, copper-dependent metalloenzymes, including particulate methane monooxygenases (pMMOs), lytic polysaccharide monooxygenases (LPMOs) and binuclear copper enzymes PHM and DBM, are able to perform various challenging C-H/O-H bond activations. Meanwhile, various copper-oxygen core containing complexes have been synthetized to mimic the active species of metalloenzymes. Dioxygen activation by mononuclear copper active site may generate various copper-oxygen intermediates, including Cu(II)-superoxo, Cu(II)-hydroperoxo, Cu(II)-oxyl as well as the Cu(III)-hydroxide species. Intriguingly, all these species have been invoked as the potential active intermediates for C-H/O-H activations in either biological or synthetic systems. Due to the poor understanding on reactivities of copper-oxygen complex, the nature of active species in both biological and synthetic systems are highly controversial.

Dioxygen activations constitute one of core issues in copper-dependent metalloenzymes. Upon O2 activation, copper-dependent metalloenzymes, including particulate methane monooxygenases (pMMOs), lytic polysaccharide monooxygenases (LPMOs) and binuclear copper enzymes PHM and DBM, are able to perform various challenging C-H/O-H bond activations. Meanwhile, various copper-oxygen core containing complexes have been synthetized to mimic the active species of metalloenzymes. Dioxygen activation by mononuclear copper active site may generate various copper-oxygen intermediates, including Cu(II)-superoxo, Cu(II)-hydroperoxo, Cu(II)-oxyl as well as the Cu(III)-hydroxide species. Intriguingly, all these species have been invoked as the potential active intermediates for C-H/O-H activations in either biological or synthetic systems. Due to the poor understanding on reactivities of copper-oxygen complex, the nature of active species in both biological and synthetic systems are highly controversial.

Recently, a research team led by Prof. Binju Wang from Xiamen University, China, gauged the reactivities of various mononuclear copper-oxygen species in both biological systems and the synthetic systems. The study shows (a) the MN15 functional is highly accurate for mononuclear copper-oxygen complexes, in which the experimental kinetics of various C-H/O-H activations can be well reproduced with MN15; (b) Cu(II)-superoxo shows the consistent reactivities in both biological and synthetic systems: it is highly reactive for O-H bond activations but shows low reactivities for C-H bond activations. Thus, Cu(II)-superoxo could not be the active species for C-H activations in both biological and synthetic systems. (c) Cu(II)-hydroperoxo is inert for C-H bond activations, but its radical character on the proximal O enables it to perform HAA from moderate O-H bonds or couple with another Cu(I) to form the dinuclear copper species. Thus, Cu(II)-hydroperoxo represents a key intermediate along the O2 activation pathways rather than an oxidant for C-H activation in both biological and synthetic systems. (d) Cu(II)-oxyl is highly reactive for C-H bond activations and thus could be responsible for C-H activation in mononuclear copper monoxygenases. (e) Though the highly reactivities of copper(III)-hydroxide toward C-H bond activations have been well established, the formation of such species in monoxygenases is highly unfavorable thermodynamically. These insights are expected to provide the consistent understanding on reactivities of various copper-oxygen active species in both biological and synthetic systems. The review was published in Chinese Journal of Catalysis (https://doi.org/10.1016/S1872-2067(21)63974-8).

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About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top six journals in Applied Chemistry with a current SCI impact factor of 8.271. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

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