Robby Vroemans

Pd-catalyzed carboxylation of ethylene into sodium acrylate is an industrially relevant reaction aiming at transforming CO₂ into value-added chemicals. Herein, we combine experimental and DFT studies to understand the reactivity and catalytic performance of the Pd/dicyclohexylphoshpinoethane (dcpe) system. Combination of DMF as solvent, PdBr₂ as precursor and P(C₆FH₄)₃ as additive, permitted us to rationally improve the catalytic performance.

Abstract

Pd-catalyzed carboxylation of ethylene into sodium acrylate is an industrially relevant reaction that has gained increasing attention in the last years. By this process, CO₂ can be transformed into a value-added molecule in a single, high atom economy step. However, there is still some room for improvement since the productivity of the reference catalyst is rather low. A key aspect to achieve this goal concerns the good understanding of reaction mechanism. Herein, we combine experimental and DFT studies to gain some knowledge on the reactivity and catalytic performance of the Pd/dicyclohexylphosphinoethane (dcpe) system. First, we were able to understand the influence of the solvent on the reaction, and we demonstrated that DMF was the best candidate due to the more efficient formation of the Pd-metallalactone. Moreover, we have demonstrated that highly available and less costly PdBr₂ can be a suitable precursor, as Pd^II is reduced in situ in DMF in the presence of an excess of NaOtBu. Finally, the role of different monophosphine additives has been elucidated, which permitted us to rationally improve the catalytic performance.

Nature, Published online: 18 July 2024; doi:10.1038/d41586-024-02358-w

Synthesis
DOI: 10.1055/a-2344-5677

Palladium- and nickel-catalyzed cross-couplings are powerful methods for constructing C–C and C–N bonds, particularly through Suzuki–Miyaura and Buchwald–Hartwig reactions. Although aryl iodides, bromides, and triflates are the most commonly used substrates, aryl chlorides are less frequently utilized due to their lower reactivity. However, they are appealing because they are readily available and inexpensive. This short review highlights recent developments on the Suzuki–Miyaura and Buchwald–Hartwig cross-couplings of aryl chlorides, using both homogeneous and heterogeneous catalysis with palladium and nickel.1 Introduction2 Suzuki–Miyaura Cross-Couplings2.1 Homogeneous Palladium Catalysis2.2 Heterogeneous Palladium Catalysis2.3 Homogeneous Nickel Catalysis2.4 Heterogeneous Nickel Catalysis3 Buchwald–Hartwig Amination Reactions3.1 Homogeneous Palladium Catalysis3.2 Heterogeneous Palladium Catalysis3.3 Homogeneous Nickel Catalysis3.4 Heterogeneous Nickel Catalysis4 Conclusion
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Nature Sustainability, Published online: 08 July 2024; doi:10.1038/s41893-024-01388-6

An unprecedented class of atropisomers based on Ugi reaction that exhibit exceptional rotational barrier is reported. The versatility of our approach enables the synthesis of atropisomers “by design” and allow the conceptualization of this work in atroposelective synthesis and high-sensitivity modular balances. Single-crystal structures, combined by DFT calculations and dynamic NMR allow us to examine a plethora of π-interactions.

Abstract

Atropisomers have attracted a great deal of attention lately due to their numerous applications in organic synthesis and to their employment in drug discovery. However, the synthetic arsenal at our disposal with which to access them remains limited. The research described herein is two-pronged; we both demonstrate the use of MCR chemistry as a synthetic strategy for the de novo synthesis of a class of atropisomers having high barriers to rotation with the simultaneous insertion of multiple chiral elements and we study these unprecedented molecular systems by employing a combination of crystallography, NMR and DFT calculations. By fully exploiting the synthetic capabilities of our chemistry, we have been able to monitor a range of different types of interaction, i. e. π-π, CH–π, heteroatom-π and CD–π, in order to conduct structure-property studies. The results could be applied both to atroposelective synthesis and in drug discovery.

Hemicellulose-derived monosaccharides conversion was studied to produce furfural, HMF, levulinic acid, and anhydrosugars. The study focused on developing a kinetic model using sulfuric and formic acids as catalysts at 120–190 °C. Sulfuric acid maximized furfural yield at increased temperatures, while formic acid medium enhanced anhydrosaccharides formation and enabled maximum furfural at moderate temperatures by reducing activation energy for dehydration.

Abstract

Conversion of hemicellulose streams and the constituent monosaccharides, xylose, arabinose, glucose, mannose, and galactose, was conducted to produce value-added chemicals, including furfural, hydroxymethylfurfural (HMF), levulinic acid and anhydrosugars. The study aimed at developing a kinetic model relevant for direct post-Organosolv hemicellulose conversion. Monosaccharides served as a tool to in detail describe the kinetic behavior and segregate contribution of hydrothermal decomposition and acid catalyzed dehydration at the temperature range of 120–190 °C. Catalyst free aqueous media demonstrated enhanced formation of furanics, while elevated temperatures led to significant saccharide isomerization. The introduction of sulfuric and formic acids maximized furfural yield and significantly reduced HMF concentration by facilitating its rehydration into levulinic acid (46 mol%). Formic acid additionally substantially enhanced formation of anhydrosaccharides. An excellent correlation between modeled and experimental data enabled process optimization to maximize furanic yield in two distinct hemicellulose streams. Sulfuric acid-containing hemicellulose stream achieved the highest furfural yield after 30 minutes at 238 °C, primarily due to the high Ea for pentose dehydration (150–160 kJ mol⁻¹). Contrarily, formic acid-containing hemicellulose stream enabled maximal furfural yield at more moderate temperature and extended reaction time due to its lower Ea for the same reaction step (115–125 kJ mol⁻¹).