Metal-organic framework boosts heterogeneous electron donor-acceptor catalysis

Synergistic Integration of Proton-Coupled Electron Transfer and Heterogeneous Photocatalysis for Promoting the Synthesis of Unsymmetrical Imidazolidines

The proton-coupled electron transfer (PCET) process has garnered significant attention in photocatalysis due to its ability to facilitate challenging transformations under mild conditions. By integrating PCET into heterogeneous photocatalysts, substrates can be precisely activated through the concurrent transfer of both electrons and protons between the catalyst and reaction medium. Herein, we synthesized a novel type of carbon-nitride-based photocatalyst, which can effectively drive the reaction via the PCET mechanism, enabling the three-component synthesis of unsymmetrical imidazolidines with ease.

Enhancing Electron Donor-Acceptor Complex Photoactivation with a Stable Perylene Diimide Metal-Organic Framework

Electron donor-acceptor complexes are commonly employed to facilitate photoinduced radical-mediated organic reactions. However, achieving these photochemical processes with catalytic amounts of donors or acceptors can be challenging, especially when aiming to reduce catalyst loadings. Herein, we have unveiled a framework-based heterogenization approach that significantly enhances the photoredox activity of perylene diimide species in radical addition reactions with alkyl silicates by promoting faster and more efficient electron donor-acceptor complex formation. Besides offering broad substrate scope in alkene hydroalkylation, the newly developed heterogeneous photocatalysis substantially improves the catalyst turnover numbers in comparison to previous homogeneous photocatalytic systems and demonstrates outstanding catalyst recyclability. These research findings pave the way for the advancement of various efficient and practical organic transformations using framework-supported organocatalysts.

Stable Radicals in Dihydrophenazine Derivatives-Doped Epoxy Resin for High Photothermal Conversion

Organic radicals exhibit great potential in photothermal applications, however, their innate high reactivity with oxygen renders the preparation of stable organic radicals highly challenging. In this work, a series of co-doped radical polymers ares prepared by doping dihydrophenazine derivatives (DPPs) into the epoxy resin matrix. DPPs can form radical species through the electron transfer process, which are further stabilized by the complex 3D network structure of epoxy resin. Experimental results show that the photothermal conversion efficiency is as high as 79.9%, and the temperature can quickly rise to ≈130 °C within 60 s. Due to the excellent visible light transmittance and mechanical properties of co-doped systems, this study further demonstrates their practical applications in energy-saving solar windows and thermoelectric power generation.

Metal-Organic Layers with Photosensitizer and Pyridine Pairs Activate Alkyl Halides for Photocatalytic Heck-Type Coupling with Olefins

Photochemical generation of alkyl radicals from haloalkanes often requires strong energy input from ultraviolet light or a strong photoreductant. Haloalkanes can alternatively be activated with nitrogen-based nucleophiles through a sequential SN2 reaction and single-electron reduction to access alkyl radicals, but these two reaction steps have opposite steric requirements on the nucleophiles. Herein, we report the design of Hf12 metal-organic layers (MOLs) with iridium-based photosensitizer bridging ligands and secondary-building-unit-supported pyridines for photocatalytic alkyl radical generation from haloalkanes. By bringing the photosensitizer and pyridine pairs in proximity, the MOL catalysts allowed facile access to the pyridinium salts from SN2 reactions between haloalkanes and pyridines and at the same time enhanced electron transfer from excited photosensitizers to pyridinium salts to facilitate alkyl radical generation. Consequentially, the MOLs efficiently catalyzed Heck-type cross-coupling reactions between haloalkanes and olefinic substrates to generate functionalized alkenes. The MOLs showed 4.6 times higher catalytic efficiency than the homogeneous counterparts and were recycled and reused without a loss of catalytic activity.