Gold‐Catalyzed Asymmetric Transformation of Hydroxylated Propargylic Esters

Posted on 2 October 2023 by nCarlos D. Quintanilla, nKe Zhao, nLiming Zhangn

A one-pot transformation of hydroxylated propargylic benzoate into chiral ketones featuring an O-heterocycle is realized via sequential gold catalysis and basic hydrolysis. The gold chemistry entails tandem 3,3-sigmatropic rearrangement and asymmetric cyclization of hydroxylated allenyl ester intermediates, which is achieved via asymmetric metal-ligand cooperation. The products were formed with good enantioselectivities despite the allenyl ester intermediate is racemic.

Abstract

By combining tandem asymmetric gold catalysis and subsequent stereoconvergent hydrolysis of enol ester in a one-pot process, hydroxylated propargylic esters are converted into chiral β-oxygenated ketones with mostly good enantiomeric ratios and in largely good to excellent yields. The product chiral center is formed via stereoselective cyclization of a hydroxylated allenyl ester intermediate, which is enabled by asymmetric gold-ligand cooperation.

Selective Dehydrogenation of Formic Acid Catalyzed by Air‐Stable Cuboidal PN Molybdenum Sulfide Clusters

Posted on 2 October 2023 by

Boosting Mo₃S₄ catalysts towards H₂ production: A protocol for formic acid dehydrogenation assisted by biomimetic Mo₃S₄ clusters has been developed. Experiments and theoretical calculations pinpoint to the formate substitution products as the catalytically active species. Remarkably, the highest activity for a Mo-based homogeneous catalysts is reported.

Abstract

Formic acid is considered as a promising hydrogen storage material in the context of a green hydrogen economy. In this work, we present a series of aminophosphino and imidazolylamino Mo₃S₄ cuboidal clusters which are active and selective for formic acid dehydrogenation (FAD). Best results are obtained with the new [Mo₃S₄Cl₃(edⁱp_rp)₃](BPh₄) (4(BPh₄)) (edⁱp_rp=(2-(diisopropylphosphino)ethylamine)) cluster, which is prepared through a simple ligand exchange process from the Mo₃S₄Cl₄(PPh₃)₃(H₂O)₂ precursor. Under the conditions investigated, complex 4 ⁺ showed significantly improved performance (TOF=4048 h⁻¹ and 3743 h⁻¹ at 120 °C in propylene carbonate using N,N-dimethyloctylamine as base after 10 min and 15 min, respectively) compared to the other reported molybdenum compounds. Mechanistic investigations based on stoichiometric and catalytic experiments show that cluster 4 ⁺ reacts with formic acid in the presence of a base to form formate substituted species [Mo₃S₄Cl_3-x(OCOH)_x(edⁱp_rp)₃]⁺ (x=1–3) from which the catalytic cycle starts. Subsequently, formate decarboxylation of the partially substituted [Mo₃S₄Cl_3-x(OCOH)_x(edⁱp_rp)₃]⁺ (x=1, 2, 3) catalyst through a β-hydride transfer to the metal generates the trinuclear Mo₃S₄ cluster hydride. Dehydrogenation takes place through protonation by HCOOH to form Mo−H⋅⋅⋅HCOOH dihydrogen adducts, with regeneration of the Mo₃S₄ formate cluster. This proposal has been validated by DFT calculations.

Modular Synthesis of Phosphino Hydrazones and Their Use as Ligands in a Palladium‐Catalysed Cu‐Free Sonogashira Cross‐Coupling Reaction

Posted on 2 October 2023 by

Unlocking the potential of phosphino hydrazones: Harnessing the power of hydrazone condensation to synthesise phosphino hydrazone ligands from 3-(diphenylphosphino)propanal and commercially available aryl hydrazines and studying their palladium complexes for Cu-free Sonogashira cross-coupling reaction.

Abstract

Phosphino hydrazones represent a versatile class of nitrogen-containing phosphine ligands. Herein, we report a modular synthesis of phosphino hydrazone ligands by hydrazone condensation reaction of three different aryl hydrazines with 3-(diphenylphosphino)propanal (PCHO). Complexation reactions of these phosphino hydrazone ligands with palladium(II) and platinum(II) were investigated and the catalytic activity of the palladium(II) complexes was explored in a Cu-free Sonogashira cross-coupling reaction achieving yields up to 96 %. Additionally it was shown that the catalytically active species is homogeneous.

Bottom‐up Synthesis of Nanosheets at Various Interfaces

Posted on 2 October 2023 by nKoki Sasaki, nYoshiaki Uchida, nNorikazu Nishiyaman

Nanosheets with safety, dispersibility, and nanosized effects have been widely studied for their unique properties. This review article introduces the advantages and the uniqueness of the synthesis method of nanosheets at interfaces. Reconstructing the past literature reveals the perspectives of major challenges and opportunities associated with scalable nanosheet synthesis methods for industrial production.

Abstract

Nanostructured materials with high aspect ratios have been widely studied for their unique properties. In particular, nanosheets have safety, dispersibility, and nanosized effects, and nanosheets with exceptionally small thicknesses exhibit unique properties. For non-exfoliable materials, the bottom-up nanosheet growth using various interfaces as templates have been investigated. This review article presents the synthesis of nanosheets at the interfaces and layered structure; it explains the features of each interface type, its advantages, and its uniqueness. The interfaces work as templates for nanosheet synthesis. We can easily use the liquid-liquid and gas-liquid interfaces as the templates; however, the thickness of nanosheets usually becomes thick because it allows materials to grow in thickness. The solid-gas and solid-liquid interfaces can prevent nanosheets from growing in thickness. However, the removal of template solids is required after the synthesis. The layered structures of various materials provide two-dimensional reaction fields between the layers. These methods have high versatility, and the nanosheets synthesized by these methods are thin. Finally, this review examines the key challenges and opportunities associated with scalable nanosheet synthesis methods for industrial production.

Solvent‐Free Selective Oxidation of Benzyl Alcohol at Atmospheric Pressure Catalyzed by Pd Nanoparticles Supported on g‐C3N4 Materials with Tunable Nitrogen Distributions

Posted on 2 October 2023 by

A series of thermally exfoliated g-C₃N₄ (eg-C₃N₄) have been synthesized under various gas conditions (air/N₂) and then applied as catalyst supports to load Pd nanoparticles. In the solvent-free atmospheric selective oxidation of benzyl alcohol, 2.5Pd/eg-C₃N₄-AN catalyst afforded benzyl alcohol conversion and selectivity to benzaldehyde of 88 % and 92 %, respectively.

Abstract

Solvent-free atmospheric selective oxidation of benzyl alcohol (BZA) by molecular oxygen is a promising and green process for the synthesis of benzaldehyde (BZL). Supported Pd nanoparticles have been widely reported in the catalytic selective oxidation of BZA where the activity depends on the chemical valence and dispersion of the Pd nanoparticles. Herein, a series of thermally exfoliated g-C₃N₄ (eg-C₃N₄) have been synthesized under various gas conditions (air/N₂) and then applied as catalyst supports to load Pd nanoparticles. The physicochemical properties of the prepared Pd/eg-C₃N₄ materials have been characterized by N₂ adsorption–desorption, XRD, FT-IR, UV-vis, XPS, and TEM. Pd nanoparticles dispersed well on the supports, and the distributions of Pd and nitrogen species of the catalysts were related to the gas conditions of the supports. In the selective oxidation of BZA, 2.5Pd/eg-C₃N₄-AN catalyst afforded conversion of BZA and the selectivity to BZL of 88 % and 92 %, respectively. The metallic Pd⁰ species are considered the catalytic sites of Pd/eg-C₃N₄ in the catalytic reaction and meanwhile, the basic N_b species of eg-C₃N₄ were beneficial to the overall activity of the catalyst.

Use of Constrained G‐Quadruplexes for Enantioselective Sulfoxidation Site Mapping

Posted on 2 October 2023 by

G-quadruplexes (G-4) mediated asymmetric sulfoxidation: Asymmetric sulfoxidations were performed utilizing native or modified G-4-forming nucleic acids as chiral inductors, providing proof that asymmetric reactions can occur at distinct sites of the biomolecule, yielding different enantiomers.

Abstract

Catalysis using G-quadruplexes (G-4) has shown promise as a way to perform asymmetric sulfoxidation of thioanisole derivatives. However, despite the relative simplicity of G-4, the mechanism of chiral control of sulfoxidation is still unknown, mainly because G-4 can adopt different topologies. To better understand the mechanism of G-4-catalyzed sulfoxidation, G-4 was chemically constrained into a unique topology. It was shown that either sulfoxidation can occur at the outer tetrads or at the grooves of G-4 and that different enantiomers can be generated depending on the region where catalysis occurs. By means of these G-4 mimics, the enantioselective control of the sulfoxidation reaction was unraveled.

Solvent‐Free Aerobic Oxidative Cleavage of Methyl Oleate to Biobased Aldehydes over Mechanochemically Synthesized Supported AgAu Nanoparticles

Posted on 2 October 2023 by

A green solvent-free aerobic conversion of methyl oleate, represented by an oily droplet, to biobased aldehydes, represented by octanal and nonanal molecules by mechanochemically synthesized bimetallic nanoalloys of AgAu supported on silica.

Abstract

The performance of mechanochemically synthesized supported bimetallic AgAu nanoalloy catalysts was evaluated in the oxidative cleavage of methyl oleate, a commonly available unsaturated bio-derived raw material. An extensive screening of supports (SiO₂, C, ZrO₂, Al₂O₃), metallic ratios (Ag : Au), reaction times, temperatures, and use of solvents was carried out. The performance was optimized towards productivity and selectivity for the primary cleavage products (aldehydes and oxoesters). The optimal conditions were achieved in the absence of solvent, using Ag₈Au₉₂/SiO₂ as catalyst, at 80 °C, reaction time of 1 h, substrate to catalyst=555 and 10 bar of molecular oxygen. A strong support effect was observed: the selectivity to aldehydes was best with silica as support, and to esters was best using zirconia. This shows not only that mechanochemical preparation of bimetallic catalysts is a powerful tool to generate useful catalyst compositions, but also that a safe, green, solventless synthesis of bio-derived products can be achieved by aerobic oxidative cleavage.

Systematic in situ Investigation of the Formation of NH3 Cracking Catalysts from Precursor Perovskites ABO3 (A=La,Ca,Sr and B=Fe,Co,Ni) and their Catalytic Performance

Posted on 2 October 2023 by nSimone Gallus, nClaudia Weidenthalern

The in situ formation of ammonia decomposition catalysts derived from perovskites ABO₃ (A=La,Ca,Sr, and B=Fe,Co,Ni) was examined via operando X-ray diffraction experiments. The reduction behavior of the perovskites, the intermediate phases during activation, the catalysts’ crystallite size distribution, their morphology, and their catalytic activity were analyzed.

Abstract

This work addresses the formation of ammonia (NH₃) decomposition catalysts derived from perovskites ABO₃ (A=La, Ca, Sr, and B=Fe, Co, Ni) precursors via operando synchrotron X-ray diffraction experiments. During the reaction in NH₃, the perovskite precursors are decomposed and the transition metals are reduced. Depending on their reduction properties, active metallic catalysts are formed in situ on La₂O₃ as support. The reduction behavior of the perovskites, formation of intermediate phases during activation, and catalytic performance was studied in detail. In addition, microstructure properties such as crystallite sizes and particle morphology were analyzed. Co-/Ni-based perovskites decomposed completely during activation to Co⁰/Ni⁰ supported on La₂O₃ while Fe-based perovskites were fully stable but inactive in catalysis. This difference is due to varying electronic properties of the transition metals, e. g., decreasing electronegativity from Ni to Fe. With decreasing reducibility, the intermediate phases during activation formed more distinct. La³⁺ was partially substituted by Ca²⁺/Sr²⁺ in LaCoO₃ to test for advantageous effects in NH₃ decomposition. The best performance was observed using the precatalyst La_0.8Sr_0.2CoO₃ with a conversion of 86 % (100 % NH₃, 15000 mL g⁻¹ h⁻¹) at 550 °C.

Catalytic Properties of Nanometric Metal Overlayers with Two‐Dimensional Structures

Posted on 2 October 2023 by nHiroshi Yoshida, nMasato Machidan

Nanometric metal overlayer on the Fe−Cr−Al metal foil prepared by pulsed arc plasma deposition enables easy fabrication of metal honeycomb catalysts, and the Rh overlayer shows excellent catalytic performance for CO−NO reaction and three-way catalytic reaction. The two-dimensional structure has an advantage in NO reduction with extremely high turnover frequency.

Abstract

Although most of the currently used solid catalysts possess a three-dimensional structure of nanoparticles dispersed on a porous support, the nanoparticle structure should not be considered the optimal structure for all catalytic reactions due to some disadvantages such as thermal instability and catalyst poisoning. Herein, we present the unique catalytic performance of a two-dimensional metal foil-supported nanometric Rh thin film, referred to as the “Rh overlayer”, for a catalytic CO−NO reaction and a stoichiometric three-way catalytic reaction under practical conditions. The extremely high turnover frequency for NO reduction using two-dimensional Rh is a key to understanding this phenomenon, the detailed mechanism of which can be explained by theoretical calculations.

Front Cover: Modular Synthesis of Phosphino Hydrazones and Their Use as Ligands in a Palladium‐Catalysed Cu‐Free Sonogashira Cross‐Coupling Reaction (ChemPlusChem 10/2023)

Posted on 2 October 2023 by

The cover picture shows the three different bonding modes (mono-, bi- and tridentate) of the modular ligand towards palladium(II) or platinum(II), illustrated with Winston who kindly served as model. The cat has three binding sites (mouth, front paws and hind paws = P, N and pyridine) to bind the metal dichloride fragment. When all three are used in a tridentate bonding mode, one chlorido ligand is cleaved off. Cover design by Dr. Christoph Selg. More information can be found in the Research Article by Evamarie Hey-Hawkins and co-workers.