Bifunctional organic sponge photocatalyst for efficient cross-dehydrogenative coupling of tertiary amines to ketones

Visible light as a sole requirement for alkylation of α-C(sp3)-H of N-aryltetrahydroisoquinolines with alkylboronic acids

An alkylation of α-C(sp3)-H at N-aryltetrahydroisoquinolines with alkylboronic acids was developed under visible-light irradiation in the absence of additional photocatalyst. The reaction proceeded well, tolerating a variety of functional groups, and featured low-cost and mild reaction conditions. A preliminary mechanistic study indicated that an electron donor-acceptor (EDA) complex between an electron-rich N-aryltetrahydroisoquinoline and an electron-poor alkylboronic acid was involved in the reaction.

Riboflavin and Eosin Y Supported on Chromatographic Silica Gel as Heterogeneous Photocatalysts

The application of photocatalysis for organic synthesis, both in the laboratory and on an industrial scale, will depend on the achieving of good yields and the ease with which it can be applied. Selective irradiation of the photocatalyst with LED light has made it possible to activate the reactions easily, without the need for UV or heat filters. However, a common problem is the need to separate the photocatalyst from the reaction products through extraction and chromatography isolation processes. These procedures make it difficult to recover and reuse the catalyst, which is not compatible with scale-up applications. Photocatalysts attached to heterogeneous supports resulted in an alternative, which facilitates their removal and reuse. In this study, we use chromatographic silica gel as a low-cost heterogeneous support to bind photosensitizers such as Riboflavin or Eosin Y. The modified silica gel was analyzed by FTIR-ATR and diffuse reflectance UV-visible spectroscopy, thermogravimetric analysis, and optical microscopy. These hybrid materials have a suitable size for easy separation by decantation and were found to be photoactive against two photooxidation reactions. These easy-to-handle materials open the door to effective applications for photoinduced organic synthesis methods at medium to large scale.

Heterogeneous Photoredox Catalysis Based on Silica Mesoporous Material and Eosin Y: Impact of Material Support on Selectivity of Radical Cyclization

Heterogenization of the photocatalyst appears to be a valuable solution to reach sustainable processes. Rapid and efficient synthesis of supported photocatalyst is still a remaining challenge and the choice of the support material is crucial. The present study aims at preparing a new generation of hybrid inorganic/organic photocatalysts based on silica mesoporous material and Eosin Y. These results highlight the influence of non-covalent interactions between the material support and the reagent impacting the selectivity of the reaction.

Polydimethylsiloxane Sponge-Supported Metal Nanoparticles as Reusable Catalyst for Continuous Flow Reactions

In this manuscript, polydimethylsiloxane (PDMS) sponges supporting metal nanoparticles (gold and palladium) were developed and their catalytic properties were studied through a model reaction such as the hydrogenation of p-nitrophenol. Different synthetic conditions for gold and palladium were studied to obtain the best catalyst in terms of nanoparticle loading. The as-prepared catalysts were characterized by different techniques such as scanning electron microscopy (SEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES). The catalytic efficiency and recyclability of the supported catalyst were tested in static conditions. In addition, thanks to the porous structure of the material where the catalytic centers (metal nanoparticles) are located, the model reaction for continuous flow systems was tested, passing the reaction components through the catalyst, observing a high efficiency and recyclability for these systems.

Tethered photocatalyst-directed palladium-catalysed C-H allenylation of N-aryl tetrahydroisoquinolines

Harnessing radical intermediates in regioselective reactions presents a substantial challenge. Here, we report a novel control strategy through engineering covalently tethered transition metal-photocatalysts that conjoin Pd-phosphine and Ru/Ir photoredox units. This strategy allows us to override the innate regioselectivity of the Pd-catalysed C-H allenylation of N-aryl tetrahydroisoquinolines.

Organic dyes supported on silicon-based materials: synthesis and applications as photocatalysts

The most important advance in photocatalysis in the last decade has been the synthesis and application of organic compounds to promote this process.

Accessing oxy-functionalized N-heterocycles through rose bengal and TBHP integrated photoredox C(sp3)–O cross-coupling

A C(sp3)–O coupling strategy is described involving tautomerizable N-heterocycles (phthalazinone, pyridne, pyrimidinone and quinoxalinone) carbonyl employing rose bengal as the photocatalyst and TBHP.

The Photocatalyst-Free Cross-Dehydrogenative Coupling Reaction Enabled by Visible-Light Direct Excitation of Substrate

A new photocatalyst-free strategy for the cross-dehydrogenative C-C and C-P coupling reaction has been described. This protocol provides a concise method to synthesize various 1-substituted tetrahydroisoquinoline (THIQ) derivatives enabled by visible-light direct excitation of substrates without using any photocatalyst. Moreover, a wide substrate scope demonstrated good synthetic versatility and practicality.

Photocatalyzed Csp3-Csp3 cross-dehydrogenative coupling of N-Boc-tetrahydroisoquinolines with α,β-unsaturated ketones

A novel photocatalyzed cross-dehydrogenative coupling reaction of N-Boc-tetrahydroisoquinolines with α,β-unsaturated ketones has been developed. This research provides an easy access to a variety of C1-substituted tetrahydroisoquinolines, which can be further transformed into benzo[a]-quinolizine-2-ones, the skeletons of natural products with a wide range of biological activities. The load of the photocatalyst is low and the oxidant is inexpensive and less toxic.

Self-catalyzing photoredox polymerization for recyclable polymer catalysts

A photoactive eosin Y-derived monomer was developed that can induce photoelectron/energy transfer, while simultaneously partaking in the polymerization as a monomer, affording polymer catalysts with tunable eosin Y incorporations.

Organopolymer with dual chromophores and fast charge-transfer properties for sustainable photocatalysis

Photocatalytic polymers offer an alternative to prevailing organometallics and nanomaterials, and they may benefit from polymer-mediated catalytic and material enhancements. MPC-1, a polymer photoredox catalyst reported herein, exhibits enhanced catalytic activity arising from charge transfer states (CTSs) between its two chromophores. Oligomeric and polymeric MPC-1 preparations both promote efficient hydrodehalogenation of α-halocarbonyl compounds while exhibiting different solubility properties. The polymer is readily recovered by filtration. MPC-1-coated vessels enable batch and flow photocatalysis, even with opaque reaction mixtures, via "backside irradiation." Ultrafast transient absorption spectroscopy indicates a fast charge-transfer process within 20 ps of photoexcitation. Time-resolved photoluminescence measurements reveal an approximate 10 ns lifetime for bright valence states. Ultrafast measurements suggest a long CTS lifetime. Empirical catalytic activities of small-molecule models of MPC-1 subunits support the CTS hypothesis. Density functional theory (DFT) and time-dependent DFT calculations are in good agreement with experimental spectra, spectral peak assignment, and proposed underlying energetics.

Recent advances in photocatalytic manipulations of Rose Bengal in organic synthesis

This review highlights the recent advances in photocatalytic manipulations of Rose Bengal in organic synthesis.

Alkyl coupling in tertiary amines as analog of Guerbet condensation reaction

We report here that C–C coupling in tertiary amines for the synthesis of long chain and hindered amines might be efficiently performed over Pt and Pd catalysts. The mechanism study confirms similarity with the Guerbet reaction through dehydrogenation of the alkyl group and subsequent attack of the α-carbon atom by an alkyl group of another molecule. Finally, secondary amines and tertiary amines with longer alkyl chains are formed.

C–C coupling in tertiary amines for the synthesis of fatty and hindered amines proceeds efficiently over supported Pt and Pd catalysts.

Polydimethylsiloxane Sponge-Supported Nanometer Gold: Highly Efficient Recyclable Catalyst for Cross-Dehydrogenative Coupling in Water

Polydimethylsiloxane (PDMS, a stable hydrophobic polymer material) sponge-supported nanometer-sized gold can be used as a highly efficient recyclable catalyst for cross-dehydrogenative coupling of tertiary amines with various nucleophiles in water. This PDMS sponge nanometer gold catalyst can provide much better activity than the free nanometer gold in water. The reaction can be scaled up by using an easy-to-build continuous flow reactor. These results indicate the potential application of porous hydrophobic PDMS sponge material as a promising support for highly efficient recyclable catalysts in water.

A recyclable self-assembled composite catalyst consisting of Fe3O4-rose bengal-layered double hydroxides for highly efficient visible light photocatalysis in water

A novel recyclable composite catalyst (Fe₃O₄-RB/LDH) formed by stable self-assembly of Fe₃O₄ NPs, rose bengal, and layered double hydroxides can catalyze various organic transformations with high efficiency in water under visible light irradiation.