How to Harness Electrochemical Mediators for Photocatalysis – A Systematic Approach Using the Phenanthro[9,10‐<i>d</i>]imidazole Framework as a Test Case

Enders, Patrick; Májek, Michal; Lam, Chiu Marco; Little, Daniel; Francke, Robert

doi:10.1002/cctc.202200830

Cited by 5 publications

(3 citation statements)

References 104 publications

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“…To probe these ideas and explore the photochemistry, eight phenanthroimidazoles whose structures varied as a function of the substituents, were irradiated using a bank of three 405 nm LEDs. [14] Four aryl halides, Ar-X, were chosen as substrates (S), and n-Bu3N was selected as a sacrificial electron donor. Let's focus upon the excited state behavior of the Francke mediator labeled T (R 1 = R 2 = OMe), the letter standing for test case.…”

Section: Improved Properties -The "Francke Mediators"mentioning

confidence: 99%

A Challenge

Little

2023

J. Mex. Chem. Soc.

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The present contribution overviews several aspects of my groups’ involvement in the field of mediated electron transfer. From the laboratories of its pioneers to the present day, the field maintains a position of interest and fundamental importance, and is now widely accepted and utilized. I begin with a brief review of the basics where we will: differentiate mediated and direct electrolysis; highlight similarities between it and sensitized photolyses; explore the steps/stages associated with a mediated process focusing particularly upon the kinetics and thermodynamics of the electron transfer step; describe how to overcome the thermodynamic impasse that frequently accompanies electron transfer.

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Section: Improved Properties -The "Francke Mediators"mentioning

confidence: 99%

A Challenge

Little

2023

J. Mex. Chem. Soc.

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“…Although electrochemistry has long been used to study the mechanisms of organic and organometallic reactions, 31−36 almost no electrochemical exploration of photoredox processes has been reported. 37 Among the multiple photoredox catalytic reactions developed so far, those involving merged cyclic processes are particularly interesting for the versatility of synthetic solutions they provide. 38−46 The alkylation of aldehydes in the presence of olefins 46 is a typical example in which a synergistic merging of three catalytic cycles namely, photoredox, organic and hydrogen-atom transfer (HAT) cycles, respectively, as depicted in Scheme 1.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Although electrochemistry has long been used to study the mechanisms of organic and organometallic reactions, − almost no electrochemical exploration of photoredox processes has been reported …”

Section: Introductionmentioning

confidence: 99%

Monitoring and Assessing Iridium-Promoted Photoredox Catalysis by Electrochemistry

Quintaine,

Saudan,

Santoro

et al. 2023

ACS Catal.

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Recently, Professor David MacMillan introduced an original light-mediated catalytic process where simple aldehyde substrates undergo coupling with a variety of olefin partners to enantioselectively afford α-alkyl carbonyl adducts. Based on the redox potential values reported for some transient intermediates and on the knowledge-based reactivity of organic radicals, it was suggested that the alkylation of aldehydes proceeds along merged photoredox, organic, and hydrogen-atom transfer (HAT) catalytic subcycles. Inspired by this seminal work, we undertook an electrochemical investigation of the mechanism of the blue light-mediated coupling of propanal with β-pinene. The coupling reaction was performed in dimethoxyethane using Ir(dF(CF 3 )ppy) 2 (dtbbpy)](PF 6 ) as the photoredox catalyst, Nmethyl-trifluoroethanamine as the enamine catalyst precursor, and 2,4,6triisopropylbenzenethiol (ArSH) as the hydrogen atom transfer agent. Under these conditions, cyclic voltammetry and chronoamperometry allowed: (a) the determination of the redox potential values of most intermediates involved in the three catalytic cycles, including the iridium complex under its ground and excited states, (b) evidence of the in situ formation of the enamine catalyst obtained by reaction between propanal and N-methyl-trifluoroethanamine, (c) estimation of the equilibrium condensation constant between the aldehyde and the amine, (d) following the enamine oxidation by the excited iridium complex, and (e) revealing the interdependence between the photoredox and the HAT catalytic cycles. Thus, the enamine concentration, monitored by chronoamperometry, accounted for every change on the three catalytic subcycles and allowed us to assess and strengthen the occurrence of key-steps involved in the overall process. This experimental mechanistic investigation, reinforced by gas chromatography analysis of solutions obtained under synthetic conditions, fully supported MacMillan's mechanistic framework. Electrochemical methods appear to be powerful to establish the sequence of reactions triggered by photochemical activation of iridium precursors.

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Molecular Electro(Photo)Catalysis: Triarylamine and Triarylimidazole Derivatives Mediated Oxidation Systems in Organic Electrosynthesis

Liu,

Ma,

Hao

et al. 2024

Adv Synth Catal

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Organic electrosynthesis has become a green, efficient and sustainable alternative to traditional organic transformation for the redox reactions. In this connection, indirect electrolysis employing redox mediators is attaining increasing significance as it offers a chance to improve reaction selectivity and avoids the over‐oxidation/reduction issues encountered in direct electrolysis. Triarylamines and triarylimidazoles, as representative organic molecular mediators, have attracted widespread attention in recent years due to the advantages of well‐defined easy structural modification and tunable redox ability. Hence, in this minireview, the recent growth of triarylamine and triarylimidazole derivatives mediated electrochemical oxidation reactions were presented, highlighting the structural optimization, electrochemical performance and reaction mechanism of these organic mediators. Moreover, the photocatalytic and photoelectrocatalytic cases with these molecular mediators were also highlighted. To conclude, the current challenges and future prospects of this field are also discussed.

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How to Harness Electrochemical Mediators for Photocatalysis – A Systematic Approach Using the Phenanthro[9,10‐d]imidazole Framework as a Test Case

Cited by 5 publications

References 104 publications

A Challenge

A Challenge

Monitoring and Assessing Iridium-Promoted Photoredox Catalysis by Electrochemistry

Molecular Electro(Photo)Catalysis: Triarylamine and Triarylimidazole Derivatives Mediated Oxidation Systems in Organic Electrosynthesis

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