Low‐Potential Electrooxidation of Lignin Model Compounds Through Brønsted Based‐Controlled Cu/TEMPO Mediation

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Selective electrochemical (E) oxidation of lignin, due to its complex and heterogeneous structure, remains a significant challenge in its valorization. 2,2,6,6‐Tetramethylpiperidine‐1‐oxyl (TEMPO)‐mediated systems have shown promise, but their relatively high oxidation potentials and limited applicability to structurally diverse alcohols hinder broader use in lignin upgrading. In this study, we focus on elucidating the fundamental base‐controlled proton‐coupled electron transfer (PCET) kinetics during the low‐potential electrooxidation of lignin model compounds. We demonstrate that a Cu(II) complex coordinated with 2,2 ′ ‐bipyridine, denoted as (bpy)Cu(II), in combination with TEMPO, enables alcohol oxidation at significantly lower potentials than TEMPO alone, achieving a substantial cathodic shift of ~500 mV (vs. Cp 2 Fe + / 0 ). The Cu(II) center acts as a redox mediator, facilitating the generation and regeneration of the TEMPO and promoting electron transfer (ET) from alcohol substrates. We further show that the choice of Brønsted base plays a critical role in optimizing the Cu/TEMPO reactivity, as each base exhibits distinct effects depending on its basicity and compatibility with the redox environment. Systematic cyclic voltammetry studies reveal that the type of base significantly influences both oxidation potential and current, with clear correlations to the pK a of the base and the specific PCET behavior. By comparing three bases (2,6‐lutidine, 1‐methylimidazole, and triethylamine) across various alcohol substrates, including benzyl alcohol, vanillyl alcohol, methanol, and β‐O‐4 lignin model compounds, we demonstrate pronounced base‐dependent reactivity trends. This work presents selective oxidation of lignin model compounds at low potentials, offering new opportunities for the sustainable production of value‐added chemicals from biomass.

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