Anaerobic Catalyst Design for Alcohol Oxidation: Fine‐Tuning Copper/TEMPO with Bipyridine Proportions

Abstract

In this study, we investigate the indirect electro‐oxidation of benzyl alcohol using the Copper/TEMPO catalytic system, which combines copper complexes with 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO) in an anaerobic medium. We reexamine the impact of bpy ligand proportions, exploring ratios of 1:1, 2:1, 3:1, and 4:1 on catalytic activity. Cyclic voltammetry and visible spectroscopy reveal distinct electrochemical characteristics and complex formations at different bpy ratios. Simulations uncover intricate energy equilibria involving ion coordination, varying with oxidation state and bpy proportion. Theoretical and experimental spectra align, supporting the proposed structures. The Brønsted base, triethylamine (TEA), essential in this anaerobic system, shows different voltammetric profiles with each ligand ratio, revealing key interactions with bpy complexes. In the presence of benzyl alcohol, the 1:1 and 2:1 ratios exhibit indirect catalytic activity, with the 2:1 ratio yielding significantly higher current densities. This establishes a new optimal condition where [Cu(bpy)₂]²⁺ formed in a 2:1 stoichiometry demonstrates superior activity with a lower redox potential, while maintaining labile coordination points for necessary interactions. Theoretical results also indicate weaker TEMPO coordination to [Cu(bpy)₂]²⁺.