Chemistry - An Asian Journal最新文献

Reaction of lanthanoid tris(3,5-dimethylpyrazolate) compounds, [Ln(Me₂pz)₃(thf)]₂ (Ln=La 1 a, Ce, Pr, Dy 1 b, Yb, Lu) with potassium or lithium bistrimethylsilylamide and with or without added 3,5-dimethylpyrazole, or of lanthanoid tris(bistrimethylsilyl)amide complexes with potassium bistrimethylsilylamide and 3,5-dimethylpyrazole have yielded a variety of oxide centred Ln₃ or Ln₄/(K or Li)_1-3 multinuclear cages, namely, [La₄O(Me₂pz)₁₁ K(thf)₂] (2 a), [La₄O(Me₂pz)₁₁Li(Me₂pzH)]⋅0.5Hexane (2 b), [La₄O(Me₂pz)₁₀(Me₂pzH)] (2 c) (from heating 1 a in toluene), [Ce₃O(Me₂pz)₉K₂(dme)₂] (3 a), [Ce₃O(Me₂pz)₉Li₂(thf)₂]⋅0.5Hexane (3 b) and [Ce(Me₂pz)₅Li₂(thf)₃] (3 c), which crystallized together, [Ce₃O(Me₂pz)₁₀K₃(thf)₃] (3 d), [Pr₃O(Me₂pz)₁₀K₃(thf)₃] (4), [Dy₃O(Me₂pz)₉K₂(thf)₂]⋅THF (5), [Yb₃O(Me₂pz)₉K₂(thf)₂]⋅THF (6), and [Lu₃O(Me₂pz)₉K₂(thf)₂]⋅THF (7). Crystals of {[K₈(Me₂pz)₈(thf)₂]⋅THF}_∞ (8) were also obtained from the preparation of 7. From reaction of [Ce(Me₂pz)₃(thf)]₂ with potassium tert-butoxide in toluene, the cerium(IV) heterobimetallic polymer [Ce₂(Me₂pz)₆(OtBu)₄K₂]_∞ (9) was isolated. In the Ln₃O and the Ln₄O cages, the Ln atoms have triangular and distorted tetrahedral arrangements about the central oxygen, respectively. The relationship of the alkali metals to the central oxygen varies considerably. Thus in 2 a, 2 b, there is no bonding, in 3 a, both K atoms interact weakly, in 3 b one of the two Li atom is bound, in 3 d, 4, one of three K atoms in bound, whilst in 5-7, both K atoms are bound. All metals are bound to the cages by a variety of pyrazolate binding modes, with up to five different exhibited in some structures, and a new coordination mode, μ₄-1κ(N):2κ(N'):η⁵:η⁵, was observed in two complexes. In the structure of 2 c, the coordinated Me₂pzH ligand binds to two metals through a single nitrogen, the first time this has been observed for a pyrazole donor. The complex 9 is polymeric with all metals bridged by butoxide donors as well as by Me₂pz groups.

Heteroatom-doped porous carbons (HPCs) have been considered promising electrode materials for supercapacitors due to their improvement of energy density by providing extra pseudocapacity. Covalent organic frameworks (COFs) are obtaining great importance in energy storage because of their designable structure and versatile functionality. Herein, we designed and fabricated oxygen and sulfur dual-doped covalent organic framework (COF) derived HPCs with very high heteroatoms content (up to 25.76 atom%) via a facile coupling reaction. The optimized HPCs exhibit a porous structure with high specific surface area (up to 2835 m² g^-1) along with a high specific capacitance (430 F g^-1 at 0.5 A g^-1), excellent capacitance retention (96.9 %), and high coulombic efficiency (98.5 %) after 10000 cycles at 5 A g^-1. As electrodes for aqueous symmetric supercapacitors, the HPCs exhibits a high energy density of 60 Wh kg^-1 at a 250 W kg^-1 power density, excellent cycling stability of capacity retention (82.2 %) and a high coulombic efficiency (92.3 %) after 10000 cycles at 10 A g^-1, indicating attractive application potential in chemical energy storage. This work establishes a promising strategy for preparation of high heteroatom content HPCs using COFs and demonstrates great potential for energy storage/conversion devices.

Multidentate bis-NHCs ligands with various spacers are expected to combine the advantages of coordination chemistry and catalysis. These offer opportunities to construct various organometallic frameworks involving transition metals and main group elements. Therefore, developing a general procedure for synthesizing a variety of carbene salt precursors using a convenient technique is key in this context. The extended protocol of a solvent-free approach for synthesizing various bridged bis-imidazolium carbene salts, including tris and tetrakis-imidazolium precursors, is reported here. This method can be performed in the laboratory, leading to high yields (80-95 %) and isolated as analytically pure, multigram, bench-stable compounds.

The history of life's formation and the origin of its stereochemistry are nearly as multifaceted as the life itself. In this review, we focus on analyzing the step-by-step path leading to what we can define as "life" in parallel to what we know about the emergence of enantiomeric imbalance and subsequent transition to full homochirality. We start at the level of assembly of the building blocks of life from inorganic molecules and build up to the polymerization and formation of nucleic acids and peptides. We report and analyze different theories at various stages of this development and try to elucidate the most plausible theory.

A diaminomethylenemalononitrile organocatalyst efficiently promoted the asymmetric conjugate addition of cyclic β-keto esters to (E)-β-nitroacrylate derivatives, yielding the corresponding β-nitro esters derivatives with excellent enantioselectivities (up to >99 % ee). This is the first successful example of highly stereoselective conjugate addition of cyclic β-keto esters to (E)-β-nitroacrylate derivatives to obtain anti-isomers.

With the interest and knowing the importance of ferrocenyl conjugates, a direct amidation of ferrocenyl aldehyde has been developed under feasible conditions. Varieties of amines has been oxidatively coupled with ferrocene aldehyde in the presence of highly economical and robustly stable iron chalcogenide ironcarbonyl clusters [Fe₃E₂(CO)₉, E= S, Se, and Te] and TBHP. The reaction worked in greener solvent water at a moderate temperature of 70 °C and the ferrocenyl-amides in just 30 minutes. All the varieties of amines were found to be well tolerated for the present method, and due to the high medicinal importance of ferrocenyl-amides, sole focus of this report was concentrates on the synthesis of various new ferrocenyl-amides in good to excellent amounts.

A catalytic system comprising a gold(I) complex with an N-heterocyclic carbene (NHC) ligand in an ionic liquid as solvent exhibits higher catalytic efficiency compared to state of the art systems in the title reaction, which enables using down to 0.01 mol % gold. A commercial gold(I) catalyst such as IPrAuNTf₂ can be employed for this purpose. In the case of less reactive substrates bearing electron-withdrawing substituents at the phenol moiety, a tailor made NHC-gold(I) precatalyst exhibits improved reactivity and can be advantageously employed compared to the commercial one.

Herein, we report an inexpensive first-row transition metal Ni heterogeneous catalytic system for the C_sp ³-mono alkylation of fluorene using alcohols as alkylating agents via borrowing hydrogen strategy. The catalytic protocol displayed versatility with high yields of the desired products using various types of primary alcohols, including aryl/hetero aryl methanols, and aliphatic alcohols as alkylating agents. The catalyst Ni NPs@N-C was synthesized via high-temperature pyrolysis strategy, using ZIF-8 as the sacrificial template. The Ni NPs@N-C catalyst was characterized by XPS, HR-TEM, HAADF-STEM, XRD and ICP-MS. The catalyst is stable even in the air at room temperature, displayed excellent activity and could be recycled 5 times without appreciable loss of its activity.

Oxygen evolution reaction (OER) is the rate-limiting step in water electrolysis due to its sluggish kinetic, and it is challenging to develop an OER catalyst that could work efficiently in both acid and alkaline environment. Herein, NiIr nanowire assembles (NAs) with unique nanoflower morphology were prepared by a facile hydrothermal method. As a result, the NiIr NAs exhibited superior OER activity in both acid and alkaline media. Specifically, in 0.1 M HClO₄, NiIr NAs presented a superior electrocatalytic performance with a low overpotential of merely 242 mV at 10 mA cm^-2 and a Tafel slope of only 58.1 mV dec^-1, surpassing that of commercial IrO₂ and pure Ir NAs. And it achieved a significantly higher mass activity of 148.40 A/g at -1.5 V versus RHE. In 1.0 M KOH, NiIr NAs has an overpotential of 291 mV at 10 mA cm^-2 and a Tafel slope of 42.1 mV dec^-1. Such remarkable activity makes the NiIr NAs among the best of recently reported representative Ir-based OER electrocatalysts. Density functional theory (DFT) calculations confirmed alloying effect promotes surface bonding of NiIr with oxygen-containing reactants, resulting in excellent catalytic properties.

Effective separation of hexane (C6) isomers is critical for a variety of industrial applications but conventional distillation methods are energy-intensive. Adsorptive separations based on porous coordination polymers (PCPs) offer a promising alternative due to their exceptional porosity and tunable properties. However, there is still an urgent need to develop PCPs with high stability and separation performance. This study investigates how substituting a methyl (-CH₃) group with a trifluoromethyl (-CF₃) group can regulate pores and hydrophobicity in PCPs. This precise adjustment aims to enhance stability and improve the kinetic separation performance of hydrophobic C6 isomers by considering the size and hydrophobicity of the trifluoromethyl group. Two isostructural PCPs with pcu topology, PCP-CH3 and PCP-CF3, were synthesized to vary pore diameters and hydrophobicity based on the presence of -CH₃ or -CF₃ groups. PCP-CF3 showed greater stability in water compared to PCP-CH3. While PCP-CH3 had high adsorption capacities, it lacked selectivity, whereas PCP-CF3 demonstrated improved selectivity, particularly in excluding dibranched isomers. Dynamic column separation experiments revealed that PCP-CF3 could selectively adsorb linear and monobranched isomers over dibranched isomers at room temperature. These findings highlight the potential of fluorine-modified PCPs for efficient isomer separation and underscore the importance of stability improvement strategies.