Binolates as Potent Reducing Photocatalysts for Inert-Bond Activation and Reduction of Unsaturated Systems

Organic Chemistry Physical Chemistry Chemistry Catalysis
photocatalysis reduction reactions inert bond activation unsaturated systems Binolates

Academic Background

In the field of photocatalysis, the development of efficient and sustainable reducing catalysts has long been a significant research focus. Organic anions have attracted considerable attention in recent years due to their sustainability and strong reducing abilities. However, traditional phenolates are limited in their application as reducing photocatalysts owing to the high electronegativity of oxygen and the high reactivity of the resulting phenoxy radicals. As a result, researchers have been searching for more strongly reducing and easily accessible organic anion catalysts.

1,10-Bi-2-naphthol derivatives (binolates) have long been widely used in the fields of asymmetric catalysis and molecular recognition, but their potential as photocatalysts has yet to be fully explored. This study is the first to discover that binolates can serve as efficient reducing photocatalysts for the activation of inert bonds and reduction of unsaturated systems. This breakthrough not only expands the application scope of binolates but also offers new prospects for the development of organic polyanions as photocatalysts in the future.

Source of the Paper

This paper is jointly authored by Can Liu, Yan Zhang, and Rui Shang from the University of Science and Technology of China and The University of Tokyo. The article was published in Chem on April 10, 2025, under the title “Binolates as Potent Reducing Photocatalysts for Inert-Bond Activation and Reduction of Unsaturated Systems.” The corresponding author is Rui Shang, whose contact information is rui@chem.s.u-tokyo.ac.jp.

Research Process

1. Catalyst Design and Screening

The researchers first designed a series of 3,3’-substituted binolates and predicted their electronic structures and reducing abilities through theoretical calculations. Density Functional Theory (DFT) calculations revealed that 3,3’-di(triphenylsilyl) binolate (B-6) and 3,3’-di(4-tert-butylphenyl) binolate (B-3) have relatively low LUMO (lowest unoccupied molecular orbital) energy levels, suggesting they possess strong reducing power.

2. Development of Photocatalytic Reactions

The researchers selected benzotrifluoride (PhCF3) as a model substrate to develop a photocatalytic defluoroalkylation reaction. The reaction conditions included: B-6 as the catalyst (10 mol%), KOtBu (40 mol%), 1-adamantanethiol (1-AdSH, 20 mol%), K2CO3 (1.0 equiv), PhCF3 (0.2 mmol), alkene (0.6 mmol), in deoxygenated DMF, irradiated with 440 nm LED light for 24 hours. After the reaction, product yields were determined by NMR.

3. Substrate Scope Expansion

The researchers further expanded the substrate scope of the reaction, including various alkenes, dienes, ethyl difluoroacetate, and ethyl pentafluoropropionate. Experimental results showed that B-6 exhibited high catalytic activity across diverse substrates, and notably, it could still catalyze defluoroalkylation reactions under green light (525 nm).

4. Mechanistic Studies

Using UV-Vis absorption spectroscopy, cyclic voltammetry (CV), and fluorescence lifetime measurements, the researchers investigated the photophysical and electrochemical properties of B-6 in detail. Results indicated that excited B-6 has strong reducing power (Ered* = -2.84 V vs. SCE), with an excited state lifetime of 1.26 ns. Furthermore, Stern-Volmer quenching experiments confirmed that the excited state of B-6 could be quenched by PhCF3, further supporting its feasibility as a photocatalyst.

Main Results

1. Catalyst Performance Screening

In the screening of catalysts, B-6 demonstrated the best catalytic activity, enabling a 90% yield for the defluoroalkylation product of PhCF3. By contrast, other substituted binolates (such as B-1, B-2, and B-5) exhibited lower catalytic activities, and 3,3’-di(4-nitrophenyl) binolate (B-4) showed no catalytic activity at all.

2. Results of Substrate Expansion

In the substrate expansion experiments, B-6 showed high catalytic efficiency with a range of alkenes and dienes. For instance, substrates such as vinylsilane, allyl acetate, and allyl boronate reacted smoothly, with product yields exceeding 80%. Additionally, B-6 was able to mediate defluoroalkylation reactions under green light, demonstrating its broad application potential.

3. Validation of Reaction Mechanism

Through theoretical calculations and experimental verification, the researchers proposed the photocatalytic mechanism of B-6. In its excited state, the charge-separated state of B-6 facilitates electron transfer, while the generated radical anion is stabilized through resonance and steric protection, thereby achieving an efficient catalytic cycle.

Conclusions and Significance

This study found that 3,3’-substituted binolates can serve as highly efficient reducing photocatalysts for activating inert bonds and reducing unsaturated systems. Compared with traditional phenolates, binolates possess stronger reducing power and broader light absorption, enabling effective catalysis even under green light. This discovery not only broadens the application scope of binolates but also provides new directions for the future development of organic polyanions as photocatalysts.

Research Highlights

  1. High Reducing Capability: Binolates exhibit strong reducing power in the excited state and can efficiently activate inert bonds (such as C–F bonds) and reduce unsaturated systems.
  2. Broad Application Scope: Binolates show high catalytic activity across diverse substrates, demonstrating their broad application potential.
  3. Green Light Catalysis: Unlike traditional phenolates, binolates can efficiently catalyze reactions under green light, expanding the scenarios for photocatalytic applications.
  4. Novel Catalyst Design: By tuning 3,3’-substituents, researchers successfully designed binolates with strong reducing abilities, providing new ideas for the design of organic anion catalysts.

Other Valuable Information

The experimental data and computational codes of this study are fully open, and researchers may obtain the relevant resources by contacting the corresponding author. In addition, the study was funded by the University of Science and Technology of China, and the authors thank Zhe Sun and Zhuofan Xu from Tianjin University for their support with computational resources.

Through this research, the significant potential of binolates as highly efficient reducing photocatalysts has been fully demonstrated, providing a new direction for the field of photocatalysis. In the future, researchers will further explore the application of binolates in asymmetric catalysis and organic synthesis, promoting the further development of organic polyanion catalysts.