Mechanistic Studies of Electrode-Assisted Catalytic Oxidation by Flavinium and Acridinium Cations

Yang, Xin; Walpita, Janitha; Mirzakulova, Ekaterina; Shameema, Oottikkal; Hadad, Christopher M.; Glusac, Ksenija D.

doi:10.1021/cs5005135

Cited by 18 publications

(31 citation statements)

References 93 publications

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“…We recently reported that a simple, flavin‐based iminium ion (derived from EtFlOH, Scheme ) facilitates the electrocatalytic water oxidation, and we postulated that the catalysis occurs in cooperation with the surface oxides formed on the working electrode . To facilitate spectroscopic studies of the catalytic process, we are interested in developing a fully homogeneous catalyst that consists of covalently linked iminium ions (R + ) and whose oxidation mechanism follows the steps presented in Scheme a.…”

Section: Methodsmentioning

confidence: 99%

Pourbaix diagrams in weakly coupled systems: a case study involving acridinol and phenanthridinol pseudobases

Walpita

Yang

Khatmullin

et al. 2015

J of Physical Organic Chem

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The thermodynamics of proton‐coupled electron transfer (PCET) in weakly coupled organic pseudobases was investigated using 2,7‐dimethyl‐9‐hydroxy‐9‐phenyl‐10‐tolyl‐9,10‐dihydroacridine (AcrOH) and 6‐phenylphenanthridinol (PheOH) as model compounds. Pourbaix diagrams for two model compounds were constructed using the oxidation potentials and the pKa values obtained, respectively, from cyclic voltammetry and photometric titrations. Our comparative study reveals the importance of having the redox active –N center closer to –OH functionality on the thermodynamics of PCET process: PheOH exhibits a wider range of pH values (pH = 2.8 to 13.3) in which both the alcohol and the corresponding alkoxy radical are expected to coexist in solution. This result indicates that a concerted mechanism is more likely to be discovered in pseudobases analogous to PheOH. The thermochemical data also indicate that the concerted PCET mechanism cannot be achieved if water is used as the proton acceptor: assuming the pKa of hydronium ions as −1.7, the PCET involving PheOH or AcrOH as proton/electron donors and water as the proton acceptor is expected to follow the stepwise ET/PT mechanism. Copyright © 2015 John Wiley & Sons, Ltd.

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Section: Methodsmentioning

confidence: 99%

Pourbaix diagrams in weakly coupled systems: a case study involving acridinol and phenanthridinol pseudobases

Walpita

Yang

Khatmullin

et al. 2015

J of Physical Organic Chem

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“…However, another cationic iminium derivative, N -methyl-9-phenyl-acridinium ( Acr + , Figure 1 ), was found inactive toward the oxidation of water. 12 …”

Section: Introductionmentioning

confidence: 99%

Novel Fully Organic Water Oxidation Electrocatalysts: A Quest for Simplicity

Klein

Killian

et al. 2018

ACS Omega

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Despite the growing need for readily available and inexpensive catalysts for the half-reactions involved in water splitting, water oxidation and reduction electrocatalysts are still traditionally based on noble metals. One long-standing challenge has been the development of an oxygen evolution reaction catalyzed by easily available, structurally simple, and purely organic compounds. Herein, we first generalize the performance of the known N-ethyl-flavinium ion to a number of derivatives. Furthermore, we demonstrate an unprecedented application of different pyridinium and related salts as very simple, inexpensive water oxidation organocatalysts consisting of earth-abundant elements (C, H, O, and N) exclusively. The results establish the prospects of heterocyclic aromatics for further design of new organic electrocatalysts for this challenging oxidation reaction.

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“…[20] Our group studies organic molecular frameworks that accelerate oxidation of water to molecular oxygen. [22,23] One avenue of our research involves an investigation of the iminium and oxonium ion dimers (2R + ) as potential water oxidation electrocatalysts based on three catalytic steps: (i) 2R + + 2H 2 O → 2ROH + 2H + ; (ii) 2ROH → RO À OR + 2H + + 2e À ; and (iii) RO À OR → R + À R + + O 2 + 2e À . The second step of the catalytic cycle involves the oxidation of two ROH alcohol units to generate the peroxide RO À OR.…”

Section: Introductionmentioning

confidence: 99%

Conformational flexibility of xanthene‐based covalently linked dimers

Zoric

Kadel

Korvinson

et al. 2016

J of Physical Organic Chem

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The conformational flexibility of three covalently linked dimers consisting of two xanthene‐based moieties connected by a diphenyl ether linker was studied using NMR spectroscopy, X‐ray crystallography, and density functional theory (DFT) calculations. The three dimers interconvert as a function of pH: the doubly cationic dimer (Xan+)2 exists in acidic solutions (pH < 0.5), the mono‐alcohol monocation Xan+–Xan‐OH at intermediate pH values (pH = 1–3), and the neutral diol at the highest pH‐values (pH > 3). Each dimer exhibits conformational degrees of freedom associated with rotations of either the xanthene moiety or of the diphenyl ether (DPE) linker. The barriers for rotation of the xanthylium moiety were evaluated using DFT calculations, yielding values of 23 kcal/mol for (Xan+)2 and 11 kcal/mol for (Xan‐OH)2, respectively. The rotational barrier for the diphenyl ether linker in Xan+–Xan‐OH (15 kcal/mol) was experimentally determined using variable temperature NMR measurements. The relative orientation of the two –OH groups in (Xan‐OH)2 diol was investigated in solution and the solid state using NMR spectroscopy and X‐ray crystallography. The conformer observed in the solid state was found to be the In–Out conformer, while free rotation of the xanthenol units is thought to occur on the NMR timescale at room temperature. These studies are relevant for the design of linkers for efficient water oxidation catalysts. Copyright © 2016 John Wiley & Sons, Ltd.

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Mechanistic Studies of Electrode-Assisted Catalytic Oxidation by Flavinium and Acridinium Cations

Cited by 18 publications

References 93 publications

Pourbaix diagrams in weakly coupled systems: a case study involving acridinol and phenanthridinol pseudobases

Pourbaix diagrams in weakly coupled systems: a case study involving acridinol and phenanthridinol pseudobases

Novel Fully Organic Water Oxidation Electrocatalysts: A Quest for Simplicity

Conformational flexibility of xanthene‐based covalently linked dimers

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