Photocatalytic C−H activation and C−C coupling of monohydric alcohols

Heterogeneous Photocatalytic Strategies for C(sp3 )-H Activation

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.

Photochemical reactions of a diamidocarbene: cyclopropanation of bromonaphthalene, addition to pyridine, and activation of sp3 C-H bonds

We report unprecedented photochemistry for the diamidocarbene 1. Described within are the double cyclopropanation of 1-bromonaphthalene, the double addition to pyridine, and remarkably, the insertion into the unactivated sp3 C-H bonds of cyclohexane, tetramethylsilane, and n-pentane to give compounds 2-6, respectively. All compounds have been fully characterized, and the solid state structure of 4 was obtained using single crystal electron diffraction.

Heterostructure-Engineered Semiconductor Quantum Dots toward Photocatalyzed-Redox Cooperative Coupling Reaction

Semiconductor quantum dots have been emerging as one of the most ideal materials for artificial photosynthesis. Here, we report the assembled ZnS-CdS hybrid heterostructure for efficient coupling cooperative redox catalysis toward the oxidation of 1-phenylethanol to acetophenone/2,3-diphenyl-2,3-butanediol (pinacol) integrated with the reduction of protons to H2. The strong interaction and typical type-I band-position alignment between CdS quantum dots and ZnS quantum dots result in efficient separation and transfer of electron-hole pairs, thus distinctly enhancing the coupled photocatalyzed-redox activity and stability. The optimal ZnS-CdS hybrid also delivers a superior performance for various aromatic alcohol coupling photoredox reaction, and the ratio of electrons and holes consumed in such redox reaction is close to 1.0, indicating a high atom economy of cooperative coupling catalysis. In addition, by recycling the scattered light in the near field of a SiO2 sphere, the SiO2-supported ZnS-CdS (denoted as ZnS-CdS/SiO2) catalyst can further achieve a 3.5-fold higher yield than ZnS-CdS hybrid. Mechanistic research clarifies that the oxidation of 1-phenylethanol proceeds through the pivotal radical intermediates of •C(CH3)(OH)Ph. This work is expected to promote the rational design of semiconductor quantum dots-based heterostructured catalysts for coupling photoredox catalysis in organic synthesis and clean fuels production.

Emerging catalysts for the ambient synthesis of ethylene glycol from CO2 and its derivatives

Ethylene glycol (EG), a useful chemical raw material, has been widely applied in many aspects of modern society. The conventional preparation of ethylene glycol mainly uses the petroleum route at high temperatures and pressure. More and more approaches have been developed to synthesize EG from CO₂ and its derivatives under mild conditions. In this review, the ambient synthesis of EG from thermocatalysis, photocatalysis, and electrocatalysis is highlighted. The coal-to-ethylene glycol technology, one of the typical thermal catalysis routes for EG preparation, is relatively mature. However, it still faces some problems to be solved in industrialization. The recent progress in the development of coal-to-ethylene glycol technology is introduced. The main focus is on how to realize the preparation of EG under mild conditions. The strategies include doping promoters, modification of supports, design of catalysts with special structures, etc. Furthermore, the emerging technological progress of photocatalytic and electrocatalytic ethylene glycol synthesis under ambient conditions is introduced. Compared with the thermal catalytic reaction, the reaction conditions are milder. However, there are still many problems in large-scale production. Finally, we propose future development issues and related prospects for the ambient synthesis of EG using different catalytic routes.

Precisely Constructed Metal Sulfides with Localized Single-Atom Rhodium for Photocatalytic C-H Activation and Direct Methanol Coupling to Ethylene Glycol

Although there are many studies on photocatalytic environmental remediation, hydrogen evolution, and chemical transformations, less success has been achieved for the synthesis of industrially important and largely demanded bulk chemicals using semiconductor photocatalysis, which holds great potential to drive unique chemical reactions that are difficult to implement by the conventional heterogeneous catalysis. The performance of semiconductors used for photochemical synthesis is, however, usually unsatisfactory due to limited efficiencies in light harvesting, charge-carrier separation, and surface reactions. The precise construction of heterogeneous photocatalysts to facilitate these processes is an attractive but challenging goal. Here, single-atom rhodium-doped metal sulfide nanorods composed of alternately stacked wurtzite/zinc-blende segments are successfully designed and fabricated, which demonstrate record-breaking efficiencies for visible light-driven preferential activation of C-H bond in methanol to form ethylene glycol (EG), a key bulk chemical used for the production of polyethylene terephthalate (PET) polymer. The wurtzite/zinc-blende heterojunctions lined regularly in one dimension accelerate the charge-carrier separation and migration. Single-atom rhodium selectively deposited onto the wurtzite segment with photogenerated holes accumulated facilitates methanol adsorption and C-H activation. The present work paves the way to harnessing photocatalysis for bulk chemical synthesis with structure-defined semiconductors.