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Base-Free Aerobic Oxidation of Alcohols over Copper-Based Complex under Ambient Condition

Mei, Qingqing, Liu, Huizhen, Yang, Youdi, Liu, Hangyu, Li, Shaopeng, Zhang, Pei, Han, Buxing
ACS sustainable chemistry & engineering 2018 v.6 no.2 pp. 2362-2369
alcohols, aldehydes, alkalinity, ambient temperature, copper, ketones, ligands, oxidation
Cu-based complex formed from Cu(OAc)₂ and [2,2′]-bipyridinyl-5,5′-dicarboxylic acid diethyl ester (BPYDCDE) ligand was synthesized for the first time. It was found that the complex could catalyze aerobic oxidation of alcohols to aldehydes or ketones very efficiently without any external base at ambient temperature and pressure, and the yield of the desired product reached >99% in 2–5 h. Combination of experimental and theoretical studies showed that the ligand enhanced the electron population on the Cu center by a ligand-to-metal charge transfer (LMCT) effect, which made OAc– in the complex have the appropriate alkalinity and be a good leaving group, and the Cu center and the OAc– catalyze the reaction cooperatively. Moreover, the amount of OAc– in the complex was much less than that of the external base added in the catalytic systems reported, suggesting that the basic anion in the complex is more efficient for promoting the reaction than the external base added.