Photocatalytic Oxidative Coupling Research Articles

Boosting photocatalytic oxidative coupling of amines by a Ru-complex-sensitized metal-organic framework

Visible-light-driven selective photocatalytic organic synthesis has recently become a topic of great interest due to its environmental friendliness and sustainability. It is demanding for photocatalysis to utilize the wider range of light, such as visible light, and its performance is often plagued by the sluggish separation of photogenerated charge carriers. An approach is now reported to address these issues by incorporating light harvesting RuII-polypyridyl complexes into a semiconductor-type metal-organic framework (MIL-125). Delightedly, the obtained Ru(bpy)3@MIL-125 photocatalyst presents a remarkably stable and high photoactivity toward the selective oxidative coupling of amines under ambient air with visible light irradiation (λ > 440 nm). The mechanistic investigation unveiled that both effectively photoexcited electrons transfer from [Ru(bpy)3]Cl2 to MIL-125 and the interaction of CH bonds with superoxide radical (O2·−) play a critical role in photo-catalyzing selective aerobic oxidative coupling of amines. This work highlights a significant role of MOFs as heterogeneous photocatalysts in photocatalytic organic transformations.

Flower-like Bi2O2CO3-mediated selective oxidative coupling processes of amines under visible light irradiation

The photocatalytic selective transformation of amines is a green and cost-effective technology to obtain value-added products in chemical industry. In this work, a series of bismuth-based photocatalysts including Bi2MoO6, Bi2WO6, Bi5O7Cl, Bi5O7Br, Bi5O7I, BiPO4, BiVO4, Bi2O3 and various morphology Bi2O2CO3 (flower-like, sponge-like, plate-like and spherical) were synthesized and employed in the aerobic oxidative coupling of benzylamine. It is found that flower-like Bi2O2CO3 exhibited the highest photocatalytic activity, in which a 100% conversion of benzylamine with 99.0% selectivity of N-benzylidenebenzylamine was obtained at room temperature. Moreover, the photocatalytic oxidative coupling processes of various aromatic and aliphatic amines were further investigated, and excellent yields and selectivities of corresponding products are attained. Then, based on characterization results (XRD, SEM, BET and XPS, etc.) of catalyst, high photocatalytic activity of flower-like Bi2O2CO3 is attributed to thin nanopetals, low band gap, the morphology and large specific surface area. Finally, a possible reaction mechanism is proposed for the photocatalytic oxidative coupling of benzyl amine.

Oxygen-free water-promoted selective photocatalytic oxidative coupling of amines

A novel oxygen-free photocatalytic selective oxidative coupling of amines to produce imines was successfully performed with water as the primary oxidant at room temperature.

Conjugated HCl-doped polyaniline for photocatalytic oxidative coupling of amines under visible light

Conjugated HCl-doped polyaniline acted as an efficient visible light-responsive nonmetal photocatalyst for imine green synthesis.

Photocatalytic Aerobic Oxidative Coupling of Amines on a Metal–Organic Framework

Key words metal–organic framework - porphyrins - photocatalysis - oxidative coupling - benzylamines

Mechanistic Insights on Plasmon-Driven Photocatalytic Oxidative Coupling of Thiophenol Derivatives: Evidence for Steady-State Photoactivated Oxygen

The plasmonic electron oscillations in optically excited metallic nanoparticles result in surface confinement of photon energy over much longer time scales in comparison to the unconfined photons t...

Direct evidence of charge separation in a metal-organic framework: efficient and selective photocatalytic oxidative coupling of amines via charge and energy transfer.

The selective aerobic oxidative coupling of amines under mild conditions is an important laboratory and commercial procedure yet a great challenge. In this work, a porphyrinic metal-organic framework, PCN-222, was employed to catalyze the reaction. Upon visible light irradiation, the semiconductor-like behavior of PCN-222 initiates charge separation, evidently generating oxygen-centered active sites in Zr-oxo clusters indicated by enhanced porphyrin π-cation radical signals. The photogenerated electrons and holes further activate oxygen and amines, respectively, to give the corresponding redox products, both of which have been detected for the first time. The porphyrin motifs generate singlet oxygen based on energy transfer to further promote the reaction. As a result, PCN-222 exhibits excellent photocatalytic activity, selectivity and recyclability, far superior to its organic counterpart, for the reaction under ambient conditions via combined energy and charge transfer.

An In-Depth Study of the Use of Eosin Y for the Solar Photocatalytic Oxidative Coupling of Benzylic Amines

The direct utilization of solar light for synthetic photochemistry is a sustainable and efficient technological goal. Herein we report the first in-depth study on the use of the inexpensive organic photocatalyst eosin Y for solar photocatalysis by demonstrating the oxidative coupling of benzylic amines to form imines, a class of valuable intermediates in chemical synthesis. By the use of a unique experimental setup with a custom-built variable-intensity solar light simulator, replication of a natural-sunlight environment was achieved. The relative significance of different variables on the reaction rate constant was quantitatively evaluated through comprehensive experimental design. Reaction kinetics and mechanistic information were obtained using both a batch reactor and a spinning-disc reactor. A maximum pseudo-first-order rate constant of 1.59 × 10–3 s–1 was obtained at a maximum turnover frequency of 192 h–1 through optimization of the reaction conditions. Experiments carried out using a spinning-disc...

Conjugated Microporous Polymers with Immobilized TiO2 Nanoparticles for Enhanced Visible Light Photocatalysis

AbstractThe search for heterogeneous, visible light‐active, transition metal‐free, stable, and reusable photocatalysts for organic photoredox reactions remains a challenge for the chemists. Here, this study reports on a series of hybrid photocatalysts consisting of conjugated microporous polymer‐based organic semiconductors with immobilized TiO2 nanoparticles. The organic/inorganic semiconductor‐based hybrid photocatalytic system can enhance the photoinduced charge separation and thereby increasing the photocatalytic efficiency. As model reactions, the photocatalytic oxidative coupling reaction of amines and the selective oxidation of organic sulfides can be catalyzed with almost quantitative conversion and selectivity. The catalytic efficiency of the hybrid photocatalyst is higher than that of the pristine single photocatalytic systems as the conjugated microporous polymer and TiO2. Furthermore, the mechanistic study of the photoredox reactions is also described.

Visible light mediated photocatalytic oxidative coupling reaction of N-phenyl tetrahydroisoquinoline with β-keto acids

A visible light mediated photocatalytic oxidative coupling reaction of N-phenyl tetrahydroisoquinoline with β-keto acids has been developed. This approach provides a mild and operationally simple access to the synthesis of C1-acylmethylated tetrahydroisoquinolines.

Conjugated Microporous Poly(Benzochalcogenadiazole)s for Photocatalytic Oxidative Coupling of Amines under Visible Light.

Metal-free visible-light photocatalysts offer a clean, sustainable solution to many pressing environmental issues. Herein, we present a molecular design strategy to fine-tune the valence and conduction band levels of a series of conjugated microporous polymer networks based on poly(benzochalcogenadiazole) for heterogeneous photocatalysis. Enhanced photocatalytic efficiency was observed by altering the chalcogene moieties in the electron-accepting benzochalcogenadiazole unit of the polymer backbone structure. Photooxidative coupling of benzylamines was chosen as a model reaction. This design strategy leading to enhanced efficiency could potentially improve a wide range of photoredox reactions.

Merging of the photocatalysis and copper catalysis in metal-organic frameworks for oxidative C-C bond formation.

The direct formation of new C-C bonds through photocatalytic oxidative coupling from low reactive sp3 C-H bonds using environmentally benign and cheap oxygen as oxidant is an important area in sustainable chemistry. By incorporating the photoredox catalyst [SiW11O39Ru(H2O)]5- into the pores of Cu-based metal-organic frameworks, a new approach for merging Cu-catalysis/Ru-photocatalysis within one single MOF was achieved. The direct CuII-O-W(Ru) bridges made the two metal catalyses being synergetic, enabling the application on the catalysis of the oxidative coupling C-C bond formation from acetophenones and N-phenyl-tetrahydroisoquinoline with excellent conversion and size-selectivity. The method takes advantage of visible light photoredox catalysis to generate iminium ion intermediate from N-phenyl-tetrahydroisoquinoline under mild conditions and the easy combination with Cu-catalyzed activation of nucleophiles. Control catalytic experiments using similar Cu-based sheets but with the photoredox catalytic anions embedded was also investigated for comparison.

Aerobic Oxidation of a Tertiary Aliphatic Amine Under Visible‐Light Photocatalysis: Facile Synthesis of Methylene‐Bridged Bis‐1,3‐dicarbonyl Compounds

Lights, camera, action! An efficient protocol for the formation of methylene-bridged bis-1,3-dicarbonyl compounds has been developed through an aerobic photocatalytic oxidative coupling reaction between 1,3-dicarbonyl compounds and a tertiary aliphatic amine.