Robby Vroemans

This work features a novel catalyst comprising Cu single sites on functionalized graphite nanoplatelets for the efficient Ullmann-type C−O coupling. We efficiently demonstrated the crucial role of the pyrrole linker to enhance catalytic system reactivity and stability in the optimized reaction conditions.

Abstract

Cross-coupling reactions are of great importance in chemistry due to their ability to facilitate the construction of complex organic molecules. Among these reactions, the Ullmann-type C−O coupling between phenols and aryl halides is particularly noteworthy and useful for preparing diarylethers. However, this reaction typically relies on homogeneous catalysts that rapidly deactivate under harsh reaction conditions. In this study, we introduce a novel heterogeneous catalyst for the Ullmann-type C−O coupling reaction, comprised of isolated Cu atoms chelated to a tetraethylenepentamine-pyrrole ligand that is immobilized on graphite nanoplatelets. The catalytic study reveals the recyclability of the material, and demonstrates the crucial role of the pyrrole linker in stabilizing the Cu sites. The work expands the potential of single-atom catalyst nanoarchitectures and underscores the significance of ligands in stabilizing metals in cationic forms, providing a novel, tailored catalyst for cross-coupling chemistries.

A mechanochemical, solvent-free protocol for Tsuji–Trost allylation of O-, N-, and C-Nucleophiles using nontoxic, solid allyl trimethylammonium chloride as alternative allylating agent is presented. This method features fast reaction kinetics, very low catalyst loadings, high yields, mild conditions, and high functional group tolerance. Its potential for late-stage modifications of bioactive compounds is demonstrated through multiple examples.

Abstract

We present the first solvent-free, mechanochemical protocol for a palladium-catalyzed Tsuji–Trost allylation. This approach features exceptionally low catalyst loadings (0.5 mol %), short reaction times (<90 min), and a simple setup, eliminating the need for air or moisture precautions, making the process highly efficient and environmentally benign. We introduce solid, nontoxic, and easy-to-handle allyl trimethylammonium salts as valuable alternative to volatile or hazardous reagents. Our approach enables the allylation of various O-, N-, and C-nucleophiles in yields up to 99 % even for structurally complex bioactive compounds, owing to its mild conditions and exceptional functional group tolerance.

Synlett
DOI: 10.1055/s-0042-1751523

Just in the past few years, the application of 4CzIPN as a photocatalyst in photochemistry has been dramatically increased with its unique properties. In the literature, a variety of protocols for the synthesis of 4CzIPN have been reported. However, a practical process for the preparation of 4CzIPN with consistent quality on large scale is not available, but highly desirable to enable the robust application of this photocatalysis in industry. Herein, we detailed a practical and simple column-free chemical process amenable for the large-scale production of 4CzIPN with high quality in 91% yield. Current process was demonstrated on large scale. The similar process protocol was applicable and demonstrated for the synthesis of 3DPA2FBN on large scale.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Nature, Published online: 29 November 2023; doi:10.1038/d41586-023-03714-y

Synthesis
DOI: 10.1055/s-0043-1763620

Pyrazole-substituted pyridines have emerged as versatile bidentate ligands in transition-metal catalysis, providing opportunities to fine-tune reactivity and selectivity beyond what conventional bipyridine ligands can achieve. This review focuses on two representative pyrazolopyridine ligands: 2-(1H-pyrazol-1-yl)pyridine (1-PzPy) and 2-(1H-pyrazol-3-yl)pyridine (3-PzPy). The 1-PzPy series, characterized by a pyrazole ring serving as a weakly coordinating Lewis basic ligand, offer flexibility in ligand binding. Alternatively, the 3-PzPy series provide both L2- and LX-type binding modes, functioning as hydrogen bond donors and σ-donors, respectively. The structural diversity of pyrazolopyridine ligands enables the development of various synthetic strategies, facilitating cross-coupling, cycloaddition, photocatalytic, and asymmetric reactions. This review highlights the roles of these ligands in advancing transition-metal-catalyzed C–C and C–heteroatom bond-forming reactions.1 Introduction2 Synthesis of Pyrazolopyridine Ligands3 Applications of 1-PzPy Ligands4 Applications of 3-PzPy Ligands5 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Nature, Published online: 28 November 2023; doi:10.1038/d41586-023-03740-w

The Front Cover illustrates the conversion of O-aryl thiocarbamates to the corresponding S-aryl compounds (Newman-Kwart rearrangement, NKR) as an interstellar journey in a spaceship. The voyage from the O-aryl to the S-aryl constellation is fueled by violet light and mediated by a titanium dioxide asteroid. In their Research Article, R. Francke co-workers explored this photocatalytic approach (“P-NKR”) as a mild and useful alternative to the conventional thermochemical method. More information can be found in the Research Article by R. Francke and co-workers.

Synthesis
DOI: 10.1055/a-2193-4927

The ligand that stabilizes the metal center is crucial to its catalytic activity. Historically dominated by phosphorus and nitrogen, sulfur has long been little considered as a hetero element for stabilizing a potentially active metal center. However, this situation is changing and we are seeing more and more examples that incorporate this element. This review provides an overview of recent transition-metal-catalyzed reactions with ligands containing neutral sulfur groups, i.e. thioethers. A selection of examples published since 2013 illustrates the diversity of applications of thioether-containing ligands and shows that sulfur should be more widely used in the development of homogeneous catalysis.1 Introduction2 Phosphorus-Thioether Ligands3 Nitrogen-Thioether Ligands4 Oxygen-Thioether Ligands5 NHC-Thioether Ligands6 Cycloolefin-Thioether Ligands7 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Hexafluoropropylene dimer (HFPD) was directly employed to synthesize perfluoro alkyl/alkenyl aryl sulfides. A variety of thiophenol substrates were conveniently chlorinated by N-chlorosuccinimide (NCS); afterwards, C₆ perfluoroalkyl was introduced in the presence of cesium fluoride (Path A). Moreover, the C₆ perfluoroalkenyl was directly constructed by inorganic base-catalyzed nucleophilic substitution (Path B).

Abstract

Efficient approaches to perfluoroalkyl/alkenyl aryl sulfides were accomplished by a C−S coupling reaction under mild conditions. Hexafluoropropylene dimer was employed as a versatile building block for the perfluoroalkylation and perfluoroalkenylation of thiophenol. The application of the synthetic strategy was demonstrated by the high-yield transformation of a broad range of aryl derivatives. A plausible mechanistic explanation was proposed to elaborate the differences between the two reaction pathways. The methodology provides straightforward and convenient access to aryl sulfides constituting C₆ perfluoroalkyl and perfluoroalkenyl substituents.

The recent findings from J. Wei et al. where they developed a catalytic system to convert mixed oxygenated aromatic plastic waste into liquid organic hydrogen carriers are highlighted herein. The catalytic system comprises a physical mixture of Ru−ReO_x supported on SiO₂ and zeolite HZSM-5, which work together to break apart C−O bonds in the polymers to form cycloalkanes via hydrodeoxygenation.

Abstract

The accumulation of waste plastics in landfills and the environment, as well as the contribution of plastics manufacturing to global warming, call for the development of new technologies that would enable circularity for synthetic polymers. Thus far, emerging approaches for chemical recycling of plastics have largely focused on producing fuels, lubricants, and/or monomers. In a recent study, Junde Wei and colleagues demonstrated a new catalytic system capable of converting oxygen-containing aromatic plastic waste into liquid organic hydrogen carriers (LOHCs), which can be used for hydrogen storage. The authors utilized Ru−ReO_x/SiO₂ materials with zeolite HZSM-5 as a co-catalyst for the direct hydrodeoxygenation (HDO) of oxygen-containing aromatic plastic wastes that yield cycloalkanes as LOHCs with a theoretical hydrogen capacity of ≈5.74 wt % under mild reaction conditions. Subsequent efficiency and stability tests of cycloalkane dehydrogenation over Pt/Al₂O₃ validated that the HDO products can serve as LOHCs to generate H₂ gas. Overall, their approach not only opens doors to alleviating the severe burden of plastic waste globally, but also offers a way to generate clean energy and ease the challenges associated with hydrogen storage and transportation.

Synlett
DOI: 10.1055/a-2196-5592

Reported herein is a stereoselective route to anti-β-hydroxy sulfoxides through the reaction of epoxides with sulfenate anions. Extensive experimental/computational studies revealed the dual special roles of MgBr2·OEt2, serving to generate the bromohydrin alkoxide intermediate, which undergoes nucleophilic attack on the prochiral sulfenate in a diastereoselective manner. The present study has opened a general stereoselective synthetic route to anti-β-hydroxy sulfoxides.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Nature, Published online: 13 November 2023; doi:10.1038/d41586-023-03549-7