Reductive monoalkylation of nitro aryls in one-pot

The scope of the serendipitous reductive monoalkylation of ethyl (4-methoxy-3-nitrophenyl) acetate taking place during reduction of the nitro functionality to the corresponding primary amine when treated with hydrogen (1 atm) over Pd/C (10%) in ethanol is investigated. Upon prolonged reaction time the reaction conducted in ethanol and methanol yields significant amount of the corresponding secondary amines, while when performed in n-butanol and i-propanol it only resulted in the formation of a small amount of the corresponding secondary amines. Further development of the reductive monoalkylation reaction provided conditions that facilitate conversion of a range of different nitro aryls in one-pot to the corresponding secondary benzyl amino aryls in mostly good to excellent yields. This is accomplished by using hydrogen (1 atm) over Pd/C (10%) as reducing agent and benzaldehyde as the benzyl source combined with a stepwise reaction sequence. This chemistry was further extended to the formation of substituted benzyl amino aryls. The yields of the latter products varied dramatically depending on the substitution patterns associated with the benzaldehyde. However, by altering the reaction conditions it was possible to improve the yields of the benzylated products.     

Selective Reductive Coupling of Vinyl Azaarenes and Alkynes via Photoredox Cobalt Dual Catalysis

A visible light-induced Co-catalyzed highly regio- and stereoselective reductive coupling of vinyl azaarenes and alkynes has been developed. Notably, Hünig's base together with simple ethanol has been successfully applied as the hydrogen sources instead of commonly used Hantzsch esters in this catalytic photoredox reaction. This approach has considerable advantages for the straightforward synthesis of stereodefined multiple substituted alkenes bearing an azaarene motif, such as excellent regioselectivity (>20 : 1 for >30 examples) and stereoselectivity (>20 : 1 E/Z), broad substrate scope and good functional group compatibility under mild reaction conditions, which has been utilized in the concise synthesis of natural product monomorine I. A reasonable catalytic reaction pathway involving protolysis of the cobaltacyclopentene intermediate has been proposed based on the mechanistic studies.     

Reductive Coupling of Halomethylbenzene Derivatives by Nickel and Cobalt

Reduction of benzyl bromide, benzal chloride and benzotrichloride with a commercial nickel powder at 150°C gave bibenzyl, trans-stilbene, and trans-1,2-dichlorostilbene. The reaction intermediates 1,2-dichloro-1,2-diphenylethane for benzal chloride and 1,1,2,2-tetrachloro-1,2-diphenylethane for benzotrichloride were also isolated or detected by NMR spectroscopy. Dehalogenation of these intermediates by the nickel metal or by KI yielded the corresponding trans isomer as the main product. A commercial cobalt powder also reacted with these organic halides leading to similar results. Mechanisms for these reactions are proposed.     

A Strong-Acid-Resistant [Th6] Cluster-Based Framework for Effectively and Size-Selectively Catalyzing Reductive Amination of Aldehydes with N,N-Dimethylformamide

Utilization of N,N-dimethylformamide (DMF) as an amine source and reductant for synthesizing tertiary amines is a promising way to replace the substrates formaldehyde and dimethylamine, and it is desirable to seek porous acid-resistant catalysts for heterogeneous catalysis of this reaction. Herein, a robust metal–organic framework (MOF) {[Th₆O₄(OH)₄(H₂O)₆(BCP)₃]⋅10 DMF}_n ( 1 ) containing stacked nanocages with a diameter of 1.55 nm was constructed. Compound 1 can maintain its single-crystal structure even kept in air at 400 °C for 3 h, and in DMF or water at 200 °C for 7 days. Density functional theory (DFT) calculations suggested that the high interaction energy between the [Th₆O₄(OH)₄(H₂O)₆]¹²⁺ clusters and ligands was responsible for the excellent stability of 1 . Catalytic investigations revealed that 1 can effectively and size-selectively catalyze the reductive amination of aldehydes with DMF, and it can be reused at least five times without obvious loss in catalytic activity.     

Pd/C-catalyzed Reductive Mono-N-alkylation of Nitrophenol Derivatives in One-pot Way

A range of different nitrophenol derivatives were converted in one‐pot to the corresponding secondary alkyl aminophenols in good to excellent yields by using ketones as alkyl source and hydrogen over 10 wt% Pd/C as reducing agent. In all examples, except for one, the secondary amine was the sole alkylation product isolated. When aldehydes were used as alkyl source, the corresponding tertiary amine as a sole alkylation product was isolated.     

Carbon-Anchored Molybdenum Oxide Nanoclusters as Efficient Catalysts for the Electrosynthesis of Ammonia and Urea

The electrochemical NO₃⁻ reduction and its coupling with CO₂ can provide novel and clean routes to synthesize NH₃ and urea, respectively. However, their practical application is still impeded by the lack of efficient catalysts with desirable Faradaic efficiency (FE) and yield rate. Herein, we report the synthesis of molybdenum oxide nanoclusters anchored on carbon black (MoO_x/C) as electrocatalyst. It affords an outstanding FE of 98.14 % and NH₃ yield rate of 91.63 mg h⁻¹ mg_cat.⁻¹ in NO₃⁻ reduction. Besides, the highest FE of 27.7 % with a maximum urea yield rate of 1431.5 μg h⁻¹ mg_cat.⁻¹ toward urea is also achieved. The formation of electron-rich MoO_x nanoclusters with highly unsaturated metal sites in the MoO_x/C heterostructure is beneficial for enhanced catalytic performance. Studies on the mechanism reveal that the stabilization of *NO and *CO₂NOOH intermediates are critical for the NH₃ and urea synthesis, respectively.     

新型磷二肽尿嘧啶衍生物的合成(英)

通 过 肽 偶 联 反 应 合 成 了 一 系 列 新 型 的 含 磷 二 肽 的 尿 嘧 啶 衍 生 物， 收 率 为５６．２％ ～７２．６％ ．     

Efficient and Recyclable Reaction System for the Homocoupling of Terminal Acetylenes

Diynes were synthesized in high yields by homocoupling of terminal arylacetylenes and terminal alkylacetylenes in Cu(OAc)₂‐PEG (polyethyleneglycol) with NaOAc as a base. Cu(OAc)₂‐PEG was readily recycled via solvent precipitation with efficient recyclability.     

应用微乳法制备二氧化硅包裹钯纳米粒子

以氯钯酸为钯源,正硅酸乙酯(TEOS)为硅源,利用十六烷基三甲基溴化铵(CTAB)/正己醇/水构成的微乳体系制备了二氧化硅包裹纳米金属Pd粒子.其中Pd的粒径可在5～30 nm调变,外部SiO₂层的厚度可在5～35 nm调变.详细考察了氯钯酸和正硅酸乙酯的浓度、微乳体系中水和正己醇的量等参数对制备的Pd/SiO₂粒子的大小及形态的影响.     

Characterization of Hydrogen Adsorption on Palladium and Pd/c Using a Radiotracer

Hydrogen adsorption on palladium black and palladium supported on activated carbon was characterized by the Temperature Programmed Desorption technique (TPD) using the radiotracer tritium. It is shown that there are five energetic desorbed hydrogens with peak maxima at —50, 35, 115, 350, and 580°C. An additional peak at — 120°C hydrogen desorbed from activated carbon was observed on Pd/C. An isotopic hydrogen separation experiment was designed to demonstrate that hydrogen only dissociatively adsorbed on palladium surfaces whereas it was associatively adsorbed on activated carbon.     

天然高分子负载双金属催化剂催化硝基苯还原羰化反应

天然生物高分子材料-壳聚糖(简写为CS)负载催化刑：Si02—CS—PdCl2，利用Pd-Ni双金属协同效应和高分子载体对催化活性物种的保护，在催化硝基苯的还原碳化反应中表现出了较高的催化活性和选择性．并且尝试了催化刑的重复使用．     

Catalytic Dechlorination of Chlorobenzene in Water by Pd／Fe System

Chlorobenzene was dechlorinated by Pd/Fe bimetallic system in water through catalytic reduction. The dechlorination rate increases with increase of bulk loading of Pd due to the increase of both the surface loading of the Pd and the total surface area. For conditions with 0.005% Pd/Fe, 45% dechlorination efficiency was achieved within 5 h. The dechlorinated reaction is believed to take place on the bimetal surface in a pseudo-first-order reaction, with the rate constant being 0.0043 min^-1.     

Aryl-to-Vinyl 1,4-Nickel Migration/Reductive Cross-Coupling Reaction for the Stereoselective Synthesis of Multisubstituted Olefins

The aryl-to-vinyl nickel 1,4-migration (1,4-Ni migration) reaction has been reported for the first time. The generated alkenyl Ni species undergo a reductive coupling reaction with unactivated brominated alkanes affording a series of trisubstituted olefins. This tandem reaction exhibits mild conditions, a broad substrate scope, high regioselectivity, and excellent Z/E stereoselectivity. A series of controlled experiments have shown that the critical 1,4-Ni migration process is reversible. In addition, the alkenyl nickel intermediates obtained after migration are highly Z/E stereoselective and do not undergo Z/E isomerization. The obtained trace isomerization products are caused by the instability of the product.     

Palladium immobilized on amidoxime‐functionalized magnetic Fe3O4 nanoparticles: a highly stable and efficient magnetically recoverable nanocatalyst for sonogashira coupling reaction

We describe the synthesis of a novel Fe₃O₄/amidoxime (AO)/Pd nanocatalyst by grafting of AO groups on Fe₃O₄ nanoparticles and subsequent deposition of Pd nanoparticles. Prior to grafting of AO, the 2‐cyanoethyl‐functionalized Fe₃O₄ nanoparticles prepared through combining 2‐cyanoethyltriethoxysilane and Fe₃O₄ were treated with hydroxylamine. The AO‐grafted Fe₃O₄ nanoparticles were then used as a platform for the deposition of Pd nanoparticles. The catalyst was characterized using Fourier transform infrared spectroscopy, X‐ray diffraction, scanning and transmission electron microscopies, vibrating sample magnetometry, wavelength‐ and energy‐dispersive X‐ray spectroscopies and inductively coupled plasma analysis. Fe₃O₄/AO/Pd is novel phosphine‐free recyclable heterogeneous catalyst for Sonogashira reactions. Interestingly, the novel catalyst could be recovered in a facile manner from the reaction mixture by applying an external magnet device and recycled seven times without any significant loss in activity. Copyright © 2015 John Wiley & Sons, Ltd.     

镍催化芳烃卤化物还原性交叉偶联的反应机理(英文)

利用密度泛函理论(DFT)计算研究了镍催化的溴苯(R1)与对溴苯甲酸甲酯(R2)生成非对称联芳化合物的还原性交叉偶联反应的机理.结果表明,相对于一价镍的催化机理,零价镍作为活性催化剂更有利于反应的进行,零价镍催化剂首先与R1络合或者首先与R2络合的反应机理十分相似,其决速步在气相时的能垒分别是70.50或者49.66 kJ?mol-1.零价镍催化机理包括如下步骤:一次氧化加成;还原;二次氧化加成;还原消除以及催化剂再生.另外,计算结果还表明有机锌试剂在这个反应体系中很难生成.     

Pd纳米晶的调控合成及其在燃料电池中的应用

贵金属Pd纳米晶体的催化性能与其表面结构有着密切联系。基于目前Pd多面体纳米晶体可控合成技术的发展,Pd纳米晶体催化性能的进一步优化及其在催化领域的应用前景依然广阔。本文主要阐述了关于Pd多面体纳米晶的制备及其作为电催化剂在燃料电池中应用的最新研究进展。在介绍纳米晶体的生长机理及其表面结构与晶体形状的关系之后,重点描述了Pd多面体纳米晶体常见的几种制备方法,概述了Pd多面体纳米晶体作为催化剂在燃料电池阴极和阳极中的应用。最后总结展望了Pd多面体纳米晶体作为催化剂的研究方向及其发展前景。     

钯催化甲酸为氢源的芳硝基化合物直接加氢和一锅法酰胺化

Pd/C催化剂实现了甲酸为氢源的芳硝基化合物的直接加氢及甲酸为氢源和羰基源的一锅法芳硝基化合物的酰胺化.在芳硝基化合物的直接加氢过程中,该体系体现了很好的催化活性,实现了对同时带有其它可还原官能团的芳硝基化合物的选择性加氢,得到较高收率的胺类化合物.同时,通过提高反应温度和增加甲酸的量,实现了芳硝基化合物的加氢和甲酰化的串联反应,该体系体现了较高的催化活性.     

One-pot reductive monoalkylation of nitro aryls with hydrogen over Pd/C

A range of different nitro aryls were converted in one-pot to the corresponding secondary alkyl amino aryls in good to excellent yields by using aldehydes as alkyl source and hydrogen over Pd/C (10%) as reducing agent. In all examples, but one, the secondary amine was the sole alkylation product isolated. When formaldehyde was used as the alkyl source, substantial amount of the corresponding tertiary amine was isolated, however, by altering the reaction conditions slightly the corresponding secondary amine could be isolated in superb yield.     

The Use of 4-Phenyl-3-Thiosemicarbazone of Furfural for the Gravimetric Determination of Palladium

Abstract

The use of 4-phenyl-3-thiosemicarbazone of furfural as a gravimetric reagent for palladium is described. The optimum analytical conditions for precipitation of the palladium complex and the effect of possible interferences have been investigated.     

One-pot synthesis of recyclable palladium catalysts for hydrogenations and carbon-carbon coupling reactions

Palladium nanoparticles were generated from tetrakis(triphenylphophine)palladium in a mixture of tetra(ethylene glycol) and tetramethoxysilane (or titanium(IV) isopropoxide), then encapsulated in silica matrix (or titania matrix) by the treatment with water. The resulting heterogeneous material showed high catalytic activity in the hydrogenations of various alkene and alkynes and in the carbon-carbon cross-coupling reactions such as the Suzuki-Miyaura, the Sonogashira, the Heck-Mizoroki, and the Stille reactions.