Literature Seminar
2021/11/11 Ryo Kuroda

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Contents
1. Introduction
2. Representative Researches
1. Mechanistic Classification
2. Electrochemically Mediated PhotoredoxCatalysis (ePRC)
3. Decoupled PhotoElectroChemistry (dPEC)
4. Interfacial PhotoElectroChemistry (iPEC)
3. Summary
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Contents
1. Introduction
2. Representative Researches
1. Mechanistic Classification
2. Electrochemically Mediated Photoredox Catalysis(ePRC)
3. Decoupled PhotoElectroChemistry (dPEC)
4. Interfacial PhotoElectroChemistry (iPEC)
3. Summary3

Synthetic Organic Electrochemistry

S. R. Waldvogel et al. Chem. Sci., 2020, 11, 12386.

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Synthetic Organic Electrochemistry

P. S. Baran et al. Acc. Chem. Res. 2020, 53, 72.

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Synthetic Organic Electrochemistry6Synthetic Organic Electrochemistry

R. D. Little et al. Chem. Soc. Rev., 2014, 43, 2492.

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Photoredox Chemistry

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G. A. Molander et al. ACS Catal. 2017, 7, 2563.

Photoelectrochemical Organic Synthesis

SET( Single Electron Transfer )K. Y. Ye et al. Org. Chem. Front. 2020, 7, 131.

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Photoelectrochemical Organic Synthesis
The limitation of electrochemistry

The limitation of photoredox chemistry✔ Low conductivity of organic solvents ✔ Energy constrained✔ Unselective redox processes✔ Energy losses✔ Limited potential of mediators✔ Stoichiometric oxidant or reductant

Photoelectrochemistry✔ Atom efficient ✔ Large redox window ✔ High selectivity / energy efficiency
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Contents
1. Introduction
2. Representative Researches
1. Mechanistic Classification
2. Electrochemically Mediated PhotoRedox
Catalysis (ePRC)
3. Decoupled PhotoElectroChemistry (dPEC)
4. Interfacial PhotoElectroChemistry (iPEC)
3. Summary
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Mechanistic Classification

Electrochemical components Electrochemical components
Photochemical components Photochemical components↓↓
Interdependent roles
Separate roles

K. Y. Ye et al. Org. Chem. Front. 2020, 7, 131.

Reactions occur
atPhotoelectrodesurfaces

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Contents
1. Introduction
2. Representative Researches
1. Mechanistic Classification
2. Electrochemically Mediated PhotoRedox
Catalysis (ePRC)
3. Decoupled PhotoElectroChemistry (dPEC)
4. Interfacial PhotoElectroChemistry (iPEC)
3. Summary
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The Mechanism of ePRC

Tunable electrochemical redox + Selective light energy transfer= Transient generation of super-redox agent
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The Mechanism of ePRCReductionOxidation
K. Y. Ye et al. Org. Chem. Front. 2020, 7, 131.

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The Mechanism of ePRCOxidation
S. Lin et al. ACS Cent. Sci. 2020, 6, 13. 17−1340

Reduction

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The Example of ePRC
✔ Photoelectrocatalytic oxidation of unactivated alcohols under e-PRC
using RFT

Photochemical
Electrochemical
S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

17The Limitation of Flavin-Catalyzed
Oxidation of Alcohols✔ Flavin-Catalyzed Oxidation of Alcohols✔ R1 = Ph, p-MeO-Ph, R2 = H, Me→ Successful reaction✔ R1 = alkyl, R2 = H, alky
→ No reaction

S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

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The Decomposition of Thiourea✔ RFT + O2 or H2O2 ( BP )→ Decomposition of thiourea✔ Influence O2 > H2O2

S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

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The Decomposition of Thiourea✔ Oxidation potential 1a < 1b✔ Speed
Decomposition of thiourea >Oxidation of 1b✔ Mild conditions=S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

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Optimization✔ Electrical potential, blue LED, RFT,thiourea→ All essential
S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

21Substrate Scope✔ 2c ~ 2d
Successful reactions✔ 2jThe carboxylic acid → Affordable

S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

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Probing the Role of Thiourea✔Graph (Photoquenching of RFT )Thiourea is oxidized by RFT*✔BNo TU-2 → Z > E ( stable )TU-2 → Z < E ( stable )→ TU-2 works as radical 3 or 4
S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

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Probing the Role of Thiourea✔ Distinct odor of H2S✔ More TU-2, less desired reaction← More TU-2, more Reaction 1✔ TU-2 (40 mol%)< 4h Desired reaction < Reaction 1> 4h Desired reaction > Reaction 1

Proposedreaction（ Reaction 1 ）S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

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Probing the Role of Thiourea✔ First peaks : Including Reaction 1 ??
✔ Second peaks : Reaction 2✔ More 1b, higher second peaks→ TU-2 is catalyst✔B
5 ( 9 ) is the intermediacy

Reaction 1

S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

Reaction 225

Understanding the Role of RFT

Reaction 1✔ 6~8
No photocatalyst ( RFT )Reaction 1 predominates

S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

✔1
Reaction 1 is suppressedby the transient photoexcitedstate of RFT→ Successful reaction
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Proposed Catalytic Cycles

S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

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Short Summary✔ Photoelectrocatalytic oxidation ofunactivated alcohols under e-PRC using
RFT✔ Advantage
HAT of thiourea oxidizes previously untouchedaliphatic alcohols✔ Good PointNo O2, Reduced H2O2→ O2 promotes degradation of thiourea
H2O2 is byproductO2 in traditional method ( Flavin photocatalysis )HAT( HydrogenAtom Transfer )S. Lin et al. Angew. Chem. 2020, 59 (1), 409−417.

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Other Examples of iPEC
SN

N

Cl

N

N
N
H

NPTZ

O

TPPD

N

N

TAC+Cl
O

DDQ

ClO4

OxidativeN

Mes-Acr*OAc

ReductiveN

HATAcO

N
N

DCA

OAc
OAc
NO
NH

NO

RFT29

Contents
1. Introduction
2. Representative Researches
1. Mechanistic Classification
2. Electrochemically Mediated PhotoRedox
Catalysis (ePRC)
3. Decoupled PhotoElectroChemistry (dPEC)
4. Interfacial PhotoElectroChemistry (iPEC)
3. Summary
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The Example of dPEC
✔ Hofmann–Lçffler–Freytag (HLF) amination of C(sp3)-H bonds under dPEC

Electrochemical

Photochemical
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S. Stahl et al. Angew. Chem. 2019, 131, 6451 – 6456.

The Limitation of Previous
Electrochemical HLF amination✔ 1a → 2a
Successful reaction✔ 1b → 2bNo reaction

Reaction 1✔ Promote Reaction 1=32
S. Stahl et al. Angew. Chem. 2019, 131, 6451 – 6456.

Optimization
0.5 V✔30.5 V → Best Potential✔ 4, 5TBAI, irradiation → Essential

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S. Stahl et al. Angew. Chem. 2019, 131, 6451 – 6456.

Optimization

0.7 V✔40.7 V → Best Potential✔ 5, 6TBAI, irradiation → Essential
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S. Stahl et al. Angew. Chem. 2019, 131, 6451 – 6456.

Substrate Scope

Unactivatedaliphatic C-H
bond

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S. Stahl et al. Angew. Chem. 2019, 131, 6451 – 6456.

Proposed Mechanism

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S. Stahl et al. Angew. Chem. 2019, 131, 6451 – 6456.

Functional-Group Tolerance

Substrates
I- → I3- → I2

✔ Potential I- → I3- → I2 < Substrates→ Functional-group tolerance is achieved
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S. Stahl et al. Angew. Chem. 2019, 131, 6451 – 6456.

Short Summary✔ Hofmann–Lçffler–Freytag(HLF) amination ofC(sp3)-H bonds under dPEC
✔ Applied potential→ Regenerate iodine and remove
protons from system✔ Photoexcitation→ Cleave N-I bond
✔ Advantage= Low anodic potentials→ Mild condition,High selectivity
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S. Stahl et al. Angew. Chem. 2019, 131, 6451 – 6456.

Contents
1. Introduction
2. Representative Researches
1. Mechanistic Classification
2. Electrochemically Mediated PhotoRedoxCatalysis (ePRC)
3. Decoupled PhotoElectroChemistry (dPEC)
4. Interfacial PhotoElectroChemistry (iPEC)
3. Summary
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The Mechanism of iPEC

おっ!!サンテレビ

Reaction ofiPEC

Photoelectrode is coated in a photoresponsive material (typically,semiconductor) whose band gap corresponds to the energy of avisible-light photon
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K. Y. Ye et al. Org. Chem. Front. 2020, 7, 131.

The Mechanism of PhotoanodeCB

CB

EAPe-EF

VB
e-e-

EF：Fermi level
EAP：applied potential
CB：conduction band
VB：valance band

CBe-lighte-EFe-VBe-EAP is used to improvecharge carrier separation
upon irradiation
EAP promotes an electronfrom VB to CB

EFeElectron transfer
generate a holethat is used forreaction

VBe-eSubstrate

Substrate+・41

The Example of iPEC✔ iPEC C-H amination of electron-rich arenes with a α-Fe2O3 photoanode

Electrochemical
X. Hu et al. Nat. Catal. 2019, 2, 366 – 373.

Photochemical
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Optimization✔ 5, 6, 11, 12
HFIP, MeOH,
light, electricity→ All essencial✔7
Most optimized

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X. Hu et al. Nat. Catal. 2019, 2, 366 – 373.

Substrate Scope✔ High ortho-selectivity✔ 11, 16
Substrates with high oxidative
potentials give low yields← The oxidation was inefficient✔ 11
Extend the reaction time
≠ Achieve a high yield

X. Hu et al. Nat. Catal. 2019, 2, 366 – 373.

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Substrate Scope

High ortho-selectivity

X. Hu et al. Nat. Catal. 2019, 2, 366 – 373.

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Late-Stage Functionalization ofPharmaceuticals

X. Hu et al. Nat. Catal. 2019, 2, 366 – 373.

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Proposed Mechanism←HFIP

Hydrogen bonds→ High ortho-selectivity

X. Hu et al. Nat. Catal. 2019, 2, 366 – 373.

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Short Summary✔ iPEC C-H amination ofelectron-rich arenes with aα-Fe2O3 photoanode✔ High ortho-selectivity↑
Hydrogen bonds←HFIPintermediate✔ a-Fe2O3 photoanode + Blue LEDs
= Highly oxidizing
X. Hu et al. Nat. Catal. 2019, 2, 366 – 373.

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Summary of iPEC
✔ Advantages✔Leveraging the energy of visible light to offset the EAP→ Better selectivity and energy efficiency✔ Not only a chromophore in solution→ Substrates absorbing no visible light can be used

✔ Disadvantages✔ Energy benefits iPEC < ePRC
← ePRC can access very high redox potentials
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Contents
1. Introduction
2. Representative Researches
1. Mechanistic Classification
2. Electrochemically Mediated PhotoRedox
Catalysis (ePRC)
3. Decoupled PhotoElectroChemistry (dPEC)
4. Interfacial PhotoElectroChemistry (iPEC)
3. Summary
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SummaryAdvantages✔ Mild condition✔ Large redox window✔ High selectivity✔ Convenient energy-input tuning✔ Atom / Energy efficiency✔ No oxidant / reductant

Highly Promising Strategy!!!
✔ Greenness✔ Forming difficult chemical bonds✔ More potent catalyst✔ Meeting the specific reaction`s requirements

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Thank you for yourattention !!!

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