Zhigang Chai

A strategy for activating the carbon–carbon double bond via light-induced proton transfer is reported.

Hydroxyalkylation of benzylic C─H bonds with alcohol can not only construct C(sp ³ )─C(sp ³ ) bonds but also introduce hydroxyl groups into the organic scaffold, which offers an efficient and straightforward approach to access versatile benzylic moieties. Here we disclose a protocol of hydroxyalkylation of benzylic C─H bonds enabled by the hydrogen bonding‐assisted cage effect (HBACE). A broad scope of benzylic C─H substrates can be converted into desired products with excellent selectivity. The transformation follows a radical cross‐coupling mechanism which may be dominated by the persistent radical effect.

Hydroxyalkylation of benzylic C‒H bonds with alcohol can not only construct C(sp3)‒C(sp3) bonds but also introduce hydroxyl groups into organic scaffold, which offers an efficient and straightforward approach to access versatile benzylic moieties. Here we disclose a protocol of hydroxyalkylation of benzylic C‒H bonds enabled by hydrogen bonding‒assisted cage effect (HBACE). A broad scope of benzylic C‒H substrates can be converted into desired products with excellent selectivity. Mechanistic investigation indicates that the transformation follows a radical cross-coupling mechanism which may be dominated by the persistent radical effect.

C(sp ³ )‒H activation of alcohols enables creating new C─C bond while keeping hydroxyl group in a step and atom economic manner. Here, we disclose a protocol of coupling alcohols with alkenes for C(sp ³ )‒C(sp ³ ) bond formation via heterogeneous photocatalysis in flow. This protocol functions well with a broad scope of alcohols (primary and secondary alcohols) and alkenes with moderate to good yields. The heterogeneous photocatalysis in flow enables current methodology to be conducted even on gram scale, exhibiting great potential for industrial applications. Cleavage of α‐C(sp ³ )‒H of alcohol is induced by S ^• species on the surface of ZnIn ₂ S ₄ via hydrogen atom transfer (HAT), and this step was found to be involved in the rate‐determining step.

Light‐driven carboxylation offers a promising approach for synthesizing valuable fine chemicals under mild conditions. Here we disclose a heterogeneous photocatalytic strategy of C(sp²)−H activation of formate for hydrocarboxylation of alkenes over zinc indium sulfide (ZnIn₂S₄) under visible light. This protocol functions well with a variety of substituted styrenes with good to excellent yields; it also works for unactivated alkenes albeit with lower yields. Mechanistic studies confirm the existence of CO₂⋅⁻ as a key intermediate. It was found that C(sp²)−H activation of formate is induced by S⋅ species on the surface of ZnIn₂S₄ via hydrogen atom transfer (HAT) instead of a photogenerated hole oxidation mechanism. Moreover, both cleavage of the C(sp²)−H of HCOO⁻ and formation of a benzylic anion were found to be involved in the rate‐determining step for the hydrocarboxylation of styrene.

Activation of ubiquitous C(sp³)−H bonds is extremely attractive but remains a great challenge. Heterogeneous photocatalysis offers a promising and sustainable approach for C(sp³)−H activation and has been fast developing in the past decade. This Minireview focuses on mechanism and strategies for heterogeneous photocatalytic C(sp³)−H activation. After introducing mechanistic insights, heterogeneous photocatalytic strategies for C(sp³)−H activation including precise design of active sites, regulation of reactive radical species, improving charge separation and reactor innovations are discussed. In addition, recent advances in C(sp³)−H activation of hydrocarbons, alcohols, ethers, amines and amides by heterogeneous photocatalysis are summarized. Lastly, challenges and opportunities are outlined to encourage more efforts for the development of this exciting and promising field.

Activation of ubiquitous C(sp³)−H bonds is extremely attractive but remains a great challenge. Heterogeneous photocatalysis offers a promising and sustainable approach for C(sp³)−H activation and has been fast developing in the past decade. This Minireview focuses on mechanism and strategies for heterogeneous photocatalytic C(sp³)−H activation. After introducing mechanistic insights, heterogeneous photocatalytic strategies for C(sp³)−H activation including precise design of active sites, regulation of reactive radical species, improving charge separation and reactor innovations are discussed. In addition, recent advances in C(sp³)−H activation of hydrocarbons, alcohols, ethers, amines and amides by heterogeneous photocatalysis are summarized. Lastly, challenges and opportunities are outlined to encourage more efforts for the development of this exciting and promising field.

Splitting of alcohols into hydrogen and corresponding carbonyl compounds, also called acceptorless alcohol dehydrogenation, is of great significance for both synthetic chemistry and hydrogen production. Light‐Driven Alcohol Splitting (LDAS) by heterogeneous photocatalysis is a promising route to achieve such transformations, and it possesses advantages including high selectivity of the carbonyl compounds, extremely mild reaction conditions (room temperature and irradiation of visible light) and easy separation of the photocatalysts from the reaction mixtures. Because a variety of alcohols can be derived from biomass, LDAS can also be regarded as one of the most sustainable approaches for hydrogen production. In this Review, recent advances in the LDAS catalyzed by the heterogeneous photocatalysts are summarized, focusing on the mechanistic insights for the LDAS and aspects that influence the performance of the photocatalysts from viewpoints of metallic co‐catalysts, semiconductors, and metal/semiconductor interfaces. In addition, challenges and prospects have been discussed in order to present a complete picture of this field.

Solar-driven splitting of alcohol utilizing photocatalysts is a promising route to obtain H2 and fine chemicals. Ni nanoparticle has shown great potential for light-driven splitting of alcohol, and its size, exposed facets and electronic properties play key roles in the performance of photocatalyst. Therefore, purposefully modifying Ni is of great importance. In this report, Ni-Ag nanostructures were fabricated in situ on graphitic carbon nitride by a sequential photo-deposition method. The solar-driven hydrogen production from ethanol was dramatically enhanced on the Ni-Ag nanostructure-modified graphitic carbon nitride compared with pure Ni nanoparticle modified graphitic carbon nitride. It was found that the beneficial role of Ag is to disperse and stabilize small Ni nanoparticles, and importantly, expose catalytic sites that are less prone to accumulate ethanol decomposition products (acetate species), as proven by in situ diffuse reflectance infrared Fourier transform spectroscopy.

Rechargeable magnesium batteries (RMBs) have gained increasing attention owing to its high volumetric capacity, crust abundance, and safety from dendrite‐free characteristic. However, the lack of development of high‐performance cathode materials with long cycling stability and satisfactory capacity has greatly restricted the development of RMBs. Herein, a self‐supported, current collector‐free and soft electrode is prepared with delaminated Ti₃C₂ (d‐Ti₃C₂) and Li₄Ti₅O₁₂ nanosheets by simple vacuum filtration as flexible cathode in RMBs. Fabricated into a full cell with hybrid AlCl₃/MgCl₂/Mg(TFSI)₂ electrolyte and Mg anode (a thin Mg foil with thickness of 50 μm), the flexible cathode shows high initial specific capacity of 320 mAh g⁻¹ at 20 mA g⁻¹, excellent cycling stability (good retention even after 1000 cycles) and outstanding rate performance. Detailed mechanistic studies reveal that introduction of d‐Ti₃C₂ provide fast transport paths for electrons and Mg²⁺. The enlarged layer spacing of composited d‐Ti₃C₂ accounts for significant increment in capacity. Benefiting from above‐mentioned advantages, the best performance among Ti‐based electrode materials is realized and make wearable devices powered by RMBs possible, thus circumventing the safety issues of lithium batteries.