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Electrode Materials in Modern Organic Electrochemistry - PubMed

  • ️Wed Jan 01 2020

Review

. 2020 Oct 19;59(43):18866-18884.

doi: 10.1002/anie.202005745. Epub 2020 Aug 24.

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Review

Electrode Materials in Modern Organic Electrochemistry

David M Heard et al. Angew Chem Int Ed Engl. 2020.

Abstract

The choice of electrode material is critical for achieving optimal yields and selectivity in synthetic organic electrochemistry. The material imparts significant influence on the kinetics and thermodynamics of electron transfer, and frequently defines the success or failure of a transformation. Electrode processes are complex and so the choice of a material is often empirical and the underlying mechanisms and rationale for success are unknown. In this review, we aim to highlight recent instances of electrode choice where rationale is offered, which should aid future reaction development.

Keywords: electrocatalysis; electrochemistry; electrode; materials; organic synthesis.

© 2020 The Authors. Published by Wiley-VCH GmbH.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1

Examples of the effect of electrode materials on classic (A–D) and contemporary (E) reactions. Gr.=graphite, GC=glassy carbon; RVC=reticulated vitreous carbon.

Figure 2
Figure 2

The two limiting cases for electron‐transfer.

Figure 3
Figure 3

HER and OER overpotentials taken from Table 1 (averaged where relevant) for various electrode materials.

Figure 4
Figure 4

Solvent windows various electrode material and electrolyte combinations.33, 123, 124, 125, 126, 127, 128, 129 († current density cut‐off at j=±0.1 mA cm−2.).

Figure 5
Figure 5

Electrode passivation.

Figure 6
Figure 6

Occurrence of electrode materials used (cathode or anode) in a survey of 915 synthetic electrochemical protocols published between 2000–2017.

Figure 7
Figure 7

Product distributions arising from anodic decarboxylation on either platinum or graphite electrodes.

Figure 8
Figure 8

Mechanistic elucidation of reductive debromination on different cathode materials.

Figure 9
Figure 9

A,B) Cathode material with a high overpotential for proton reduction is necessary for attaining good selectivity for substrate reduction.

Figure 10
Figure 10

A) Increased adsorption of imine on Ag cathode leading to decomposition and dimerization avoided. B) Materials with high overpotential for CO2 reduction required for attaining highest product yields.

Figure 11
Figure 11

A) Unique electrocatalytic behaviour of Ag exploited for dechlorination of 2. with trend at different pHs. B) Proposed pH dependent adsorption mode.

Figure 12
Figure 12

A) Generation of a base on the cathode. B–D) A low overpotential for proton reduction on the counter electrode renders a milder generation of a base, which improves product yields.

Figure 13
Figure 13

Low overpotential for proton reduction on Pt counter electrode gives 6, but high overpotential on Pb means 6 is preferentially reduced to give 7.

Figure 14
Figure 14

Surface modification through in situ generation of active MoV coating on anode.

Figure 15
Figure 15

A) Cartoon of the interfacial double layer formed at a cathode; B) double layer‐controlled selectivity of nucleophile attack; C) exclusion of MeOH from double layer promotes cyclisation.

Figure 16
Figure 16

Anodic amination of arenes by Waldvogel showing unique performance of BDD anode. Cyclic voltammograms of m‐xylene (red) and m‐xylene with pyridine (blue), on platinum, glassy carbon and BDD. Green dashed box highlights the unaffected oxidation feature of xylene upon addition of pyridine on BDD anode.

Figure 17
Figure 17

A) Two possible mechanisms for the oxidative methoxylation of 9 (a) and (b) to give 10. Aldehyde 11 is formed from (c); B) ESR spectra reveal methoxyl radicals, leading to mechanism (b); C) formation of methoxyl radicals are more efficient on BDD anode in oxidation of isoeugenol.

Figure 18
Figure 18

BDD gives best yields for phenol/arene coupling reaction, which produces reactive radical intermediates.

Figure 19
Figure 19

A) Mg as sacrificial electrode leads to most efficient reactivity; B) Mg or Al as sacrificial electrode. Mg2+ proposed not to play significant role in mechanism.

Figure 20
Figure 20

Phosphine oxide deoxygenation is aided by sacrificial Al anode for in situ Lewis acid generation.

Figure 21
Figure 21

A) NHC complexes generated from an electrochemical process; B) the mechanism for their formation.

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