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Shannon S Stahl – 1st expert on this subject based on the ideXlab platform
cooperative electrocatalytic Alcohol Oxidation with electron proton transfer mediatorsNature, 2016Co-Authors: Artavazd Badalyan, Shannon S StahlAbstract:
A co-catalyst system for electrochemical Alcohol Oxidation composed of a bipyridine copper catalyst and an electron-proton-transfer mediator called TEMPO operates at much lower potential and is faster than TEMPO alone. Organic nitroxyls such as TEMPO (2,2,6,6-tetramethyl-1-piperidine N-oxyl) are effective electrocatalysts for Alcohol Oxidation across a broad range of substrates, making them promising for electro-organic synthesis applications. Their use in energy-conversion applications, however, is limited by the high electrode potentials required to generate the reactive oxoammonium species. Now Artavazd Badalyan and Shannon Stahl have developed a co-catalyst system for electrochemical Alcohol Oxidation that uses both TEMPO and a bipyridine copper catalyst. The dual catalyst requires a much lower potential than does TEMPO alone and the Alcohol Oxidation proceeds faster. This work has implications for the development of electrocatalysts composed of non-precious metals, with applications extending beyond Alcohol Oxidation. The electrochemical Oxidation of Alcohols is a major focus of energy and chemical conversion efforts, with potential applications ranging from fuel cells to biomass utilization and fine-chemical synthesis1,2,3,4,5,6,7. Small-molecule electrocatalysts for processes of this type are promising targets for further development8, as demonstrated by recent advances in nickel catalysts for electrochemical production and Oxidation of hydrogen9,10,11. Complexes with tethered amines that resemble the active site of hydrogenases12 have been shown both to catalyse hydrogen production (from protons and electrons) with rates far exceeding those of such enzymes11,13 and to mediate reversible electrocatalytic hydrogen production and Oxidation with enzyme-like performance14. Progress in electrocatalytic Alcohol Oxidation has been more modest. Nickel complexes similar to those used for hydrogen Oxidation have been shown to mediate efficient electrochemical Oxidation of benzyl Alcohol, with a turnover frequency of 2.1 per second. These compounds exhibit poor reactivity with ethanol and methanol, however15. Organic nitroxyls, such as TEMPO (2,2,6,6-tetramethyl-1-piperidine N-oxyl), are the most widely studied electrocatalysts for Alcohol Oxidation5,6,7,16,17,18,19. These catalysts exhibit good activity (1–2 turnovers per second) with a wide range of Alcohols18 and have great promise for electro-organic synthesis7. Their use in energy-conversion applications, however, is limited by the high electrode potentials required to generate the reactive oxoammonium species. Here we report (2,2′-bipyridine)Cu/nitroxyl co-catalyst systems for electrochemical Alcohol Oxidation that proceed with much faster rates, while operating at an electrode potential a half-volt lower than that used for the TEMPO-only process. The (2,2′-bipyridine)Cu(II) and TEMPO redox partners exhibit cooperative reactivity and exploit the low-potential, proton-coupled TEMPO/TEMPOH redox process rather than the high-potential TEMPO/TEMPO+ process. The results show how electron-proton-transfer mediators, such as TEMPO, may be used in combination with first-row transition metals, such as copper, to achieve efficient two-electron electrochemical processes, thereby introducing a new concept for the development of non-precious-metal electrocatalysts.
Mechanism of Copper/Azodicarboxylate-Catalyzed Aerobic Alcohol Oxidation: Evidence for Uncooperative CatalysisJournal of the American Chemical Society, 2015Co-Authors: Scott D. Mccann, Shannon S StahlAbstract:
Cooperative catalysis between CuII and redox-active organic cocatalysts is a key feature of important chemical and enzymatic aerobic Oxidation reactions, such as Alcohol Oxidation mediated by Cu/TEMPO and galactose oxidase. Nearly 20 years ago, Marko and co-workers reported that azodicarboxylates, such as di-tert-butyl azodicarboxylate (DBAD), are effective redox-active cocatalysts in Cu-catalyzed aerobic Alcohol Oxidation reactions [Marko, I. E., et al. Science 1996, 274, 2044], but the nature of the cooperativity between Cu and azodicarboxylates is not well understood. Here, we report a mechanistic study of Cu/DBAD-catalyzed aerobic Alcohol Oxidation. In situ infrared spectroscopic studies reveal a burst of product formation prior to steady-state catalysis, and gas-uptake measurements show that no O2 is consumed during the burst. Kinetic studies reveal that the anaerobic burst and steady-state turnover have different rate laws. The steady-state rate does not depend on [O2] or [DBAD]. These results, toge…
process development of cui abno nmi catalyzed aerobic Alcohol OxidationOrganic Process Research & Development, 2015Co-Authors: Janelle E Steves, Yuliya Preger, Joseph R Martinelli, Christopher J Welch, Thatcher W Root, Joel M Hawkins, Shannon S StahlAbstract:
An improved Cu/nitroxyl catalyst system for aerobic Alcohol Oxidation has been developed for the Oxidation of functionalized primary and secondary Alcohols to aldehydes and ketones, suitable for implementation in batch and flow processes. This catalyst, which has been demonstrated in a >50 g scale batch reaction, addresses a number of process limitations associated with a previously reported (MeObpy)CuI/ABNO/NMI catalyst system (MeObpy = 4,4′-dimethoxy-2,2′-bipyridine, ABNO = 9-azabicyclo[3.3.1]nonane N-oxyl, NMI = N-methylimidazole). Important catalyst modifications include the replacement of [Cu(MeCN)4]OTf with a lower-cost Cu source, CuI, reduction of the ABNO loading to 0.05–0.3 mol%, and use of NMI as the only ligand/additive (i.e., without a need for MeObpy). Use of a high flash point solvent, N-methylpyrrolidone, enables safe operation in batch reactions with air as the oxidant. For continuous-flow applications compatible with elevated gas pressures, better performance is observed with acetonitrile…
Steven L Suib – 2nd expert on this subject based on the ideXlab platform
oms 2 for aerobic catalytic one pot Alcohol Oxidation wittig reactions efficient access to α β unsaturated estersChemcatchem, 2014Co-Authors: Jagadeswara R Kona, Cecil K Kingondu, Amy R Howell, Steven L SuibAbstract:
Manganese oxide octahedral molecular sieve (OMS) materials with well-defined pores have been extensively studied over two decades due to their intriguing chemical and physical properties. OMS-2, the synthetic cryptomelane form of manganese oxide, was synthesized by a modified reflux method and was found to be highly active for obtaining α,β-unsaturated esters (up to 95 % yield and with high diastereoselectivities) from a variety of benzyl, heteroaryl, allyl and alkyl Alcohols via one-pot Alcohol Oxidation-Wittig reaction. The transformation utilizes air as the stoichiometric oxidant, and the inexpensive catalyst can be recovered and reused.
Xinquan Hu – 3rd expert on this subject based on the ideXlab platform
efficient no equivalent for activation of molecular oxygen and its applications in transition metal free catalytic aerobic Alcohol OxidationJournal of Organic Chemistry, 2007Co-Authors: Weimin Mo, Dong Xu, Zhenlu Shen, Baoxiang Hu, Xinquan HuAbstract:
tert-Butyl nitrite (TBN) was identified as an efficient NO equivalent for the activation of molecular oxygen. The unique property of TBN enabled TEMPO-catalyzed aerobic Alcohol Oxidation to be performed in high-volume efficiency. Up to a 16 000 turnover number was achieved in this transition-metal-free aerobic catalytic system. Under the optimal reaction conditions, various Alcohols were converted into their corresponding carbonyl compounds with TEMPO/HBr/TBN as catalyst. The newly developed method was suitable for the Oxidation of solid substrate Alcohols with high melting point and/or low solubility under the help of minimum solvent to form a slurry.