# Oxidation of C–H and O–H bonds by a copper complex inspired by the Cu(ii)–tyrosyl species formed in LPMOs

## TL;DR

This study explores a copper complex inspired by natural enzymes that can oxidize both C–H and O–H bonds, offering insights into how similar reactions might occur in biological systems.

## Contribution

The first example of a Cu complex with a redox-active ligand capable of oxidizing C–H bonds is presented.

## Key findings

- The [bqLCu(NEt3)]+ complex acts as a strong H-atom acceptor and reacts with both O–H and C–H substrates.
- Non-thermodynamic factors enhance the reactivity of [bqLCu(NEt3)]+ towards C–H bonds compared to other Cu complexes.
- The study provides evidence for the involvement of similar species in oxidation reactions by Cu-dependent metalloenzymes.

## Abstract

Cupric tyrosyl intermediates have been invoked as active oxidants in oxidase and oxygenase Cu-dependent metalloenzymes. Inspired by these natural oxidants, we report the proton-coupled electron transfer (PCET) reactivity of Cu complexes bound by a tridentate redox-active ONO pincer ligand and an ancillary amine ligand, [LCu(A)]n+ (L = bis(3,5-di-tert-butyl-2-hydroxyphenyl)amine; A = triethylamine (NEt3) or N,N,N′,N′-tetramethylpropane-1,3-diamine (tmpda); n = 0, 1). Analysis of the stoichiometry of the reactions indicated that the iminosemiquinone complex [sqLCu(NEt3)] acts as 1H+/1e− PCET acceptor, while the benzoquinone analogue [bqLCu(NEt3)]+ reacts in a 2H+/2e− fashion. Thermochemical analysis of the PCET reactivity of [sqLCu(NEt3)] and [bqLCu(NEt3)]+ revealed that [bqLCu(NEt3)]+ is a stronger H-atom acceptor, which led to faster PCET reactions. [bqLCu(NEt3)]+ reacted with substrates containing weak O–H bonds and, to our surprise, also abstracted H-atoms from C–H substrates. The reactivity of [bqLCu(NEt3)]+ was compared with other Cu complexes developed in our laboratory that are stronger H-atom acceptors but do not oxidize C–H substrates, suggesting that non-thermodynamic factors contribute to the enhanced reactivity of [bqLCu(NEt3)]+ towards C–H bonds. This work describes the first example of Cu complex bound by a redox-active ligand able to oxidize C–H bonds, and provides evidence of the involvement of similar species in the oxidation of organic substrates catalyzed by Cu-dependent metalloenzymes such as lytic polysaccharide monooxygenases.

This study examines the stoichiometry, thermochemistry, kinetics, and mechanism of the reactions of mononuclear Cu complexes bearing redox-active ligands with organic substrates containing C–H and O–H bonds.