Electrocatalytic Alcohol Oxidation with Ruthenium Transfer Hydrogenation Catalysts
2017
Waldie, Kate M. | Flajslik, Kristen R. | McLoughlin, Elizabeth | Chidsey, Christopher E. D. | Waymouth, Robert M.
Octahedral ruthenium complexes [RuX(CNN)(dppb)] (1, X = Cl; 2, X = H; CNN = 2-aminomethyl-6-tolylpyridine, dppb = 1,4-bis(diphenylphosphino)butane) are highly active for the transfer hydrogenation of ketones with isopropanol under ambient conditions. Turnover frequencies of 0.88 and 0.89 s–¹ are achieved at 25 °C using 0.1 mol % of 1 or 2, respectively, in the presence of 20 equiv of potassium t-butoxide relative to catalyst. Electrochemical studies reveal that the Ru–hydride 2 is oxidized at low potential (−0.80 V versus ferrocene/ferrocenium, Fc⁰/⁺) via a chemically irreversible process with concomitant formation of dihydrogen. Complexes 1 and 2 are active for the electrooxidation of isopropanol in the presence of strong base (potassium t-butoxide) with an onset potential near −1 V versus Fc⁰/⁺. By cyclic voltammetry, fast turnover frequencies of 3.2 and 4.8 s–¹ for isopropanol oxidation are achieved with 1 and 2, respectively. Controlled potential electrolysis studies confirm that the product of isopropanol electrooxidation is acetone, generated with a Faradaic efficiency of 94 ± 5%.
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