纳米多孔钯催化亚胺化合物加氢还原反应研究

本文首次研究了以H2为氢源、纳米多孔钯催化亚胺化合物的加氢还原反应.结果表明:在氢气压力为101.325 kPa,溶剂为无水乙醇,反应温度为30℃,反应时间24 h,催化剂物质的量分数为5%的条件下,纳米多孔钯可以高效催化亚胺化合物的加氢还原反应,高选择性、高产率地生成一系列仲胺,仲胺的产率在93%~96%之间.该反应官能团兼容性好,底物范围广,带有甲基、甲氧基、氰基和羟基等基团的亚胺都可以顺利发生还原反应生成相应的仲胺.催化剂重复使用5次后,活性未出现明显降低.     

磁性纳米粒子负载钯催化有机合成反应研究进展

磁性纳米粒子负载钯催化的有机合成反应,由于具有催化活性高,催化剂在外加磁场作用下即可快速分离和重复使用等特点,已引起了人们的广泛关注.综述了近年来磁性纳米粒子负载钯催化有机合成反应的研究进展,载体包括Fe3O4纳米粒子、有机小分子修饰的磁性纳米粒子、SiO2包覆的磁性纳米粒子、碳修饰磁性纳米粒子、羟基磷灰石包覆的磁性纳米粒子和有机高分子修饰的磁性纳米粒子等.     

钯不对称催化碳碘化反应合成手性二氢苯并呋喃类化合物

以Pd₂dba₃与手性氮膦配体Ld为催化剂,2-甲基烯丙基碘代芳基醚（1）为原料,THF为溶剂,在110 ℃下发生不对称碳碘化反应,合成了一系列手性二氢苯并呋喃类化合物,产率84.1%～94.8%,ee 81%～95%。产物结构经¹ H NMR, ¹³ C NMR和HR-MS( ESI)确证。      

膨胀石墨负载钯纳米颗粒催化六价铬还原反应

采用高分子辅助的浸渍还原法,制备得到膨胀石墨(EG)负载的纳米钯催化剂(Pd-EG),采用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)等手段对催化剂组成、结构、形貌和价态进行了表征,并考察了Pd-EG催化剂在六价铬还原反应中的活性.结果表明,催化剂中纳米钯颗粒均匀分散在膨胀石墨上,平均粒径为4.37 nm,金属负载量质量分数为0.446%.该催化剂对六价铬还原反应具有良好的催化性能,可将六价铬完全转化为三价铬,在pH=4.0及45℃条件下反应转化频率(TOF)达到3186 h-1;催化剂经过多次重复使用后的活性仍保持稳定.     

金/钯双金属纳米颗粒协同催化酰胺和醇间氢自转移反应中路易斯酸驱动反应路径

金属纳米颗粒,特别是金和它的双金属纳米颗粒作为强大的绿色催化剂广泛用于有机合成反应中。在一个反应体系中使用2个不同催化剂(如协同催化),在均相催化中是一个很好的策略。然而,这种方法仍在发展中。最近我们发现,金/钯双金属纳米颗粒与路易斯酸的协同催化体系可用于伯胺的N-烷基化：即酰胺与醇之间的氢自转移反应。我们详细报道了路易斯酸对该氢自转移反应的影响。结果表明,所选的路易斯酸不仅影响生成目标产物的反应路径,而且影响生成多个中间体和副产物的反应路径。弱的路易斯酸,如三氟甲磺酸碱土金属盐,非常适合酰胺的N-烷基化反应。     

钯纳米粒子在电极表面的制备及其对氧的催化还原

纳米微粒的体积效应使其成为表面纳米工程及功能化纳米结构材料制备的理想研究对象 [1～ 3] .纳米粒子具有独特的电子、催化及光学特性[4 ] ,近年来关于纳米粒子的制备及其在材料科学领域中的应用受到研究者的极大关注 .而贵金属纳米粒子由于其在催化领域中的广泛应用而成为最重要的研究对象之一[5,6 ] .电催化氧还原是一直为化学家瞩目的研究领域[7～ 9] .研究主要目的之一是寻找合适的氧电极反应催化剂 ,并使之能够应用于燃料电池中 .其中催化氧电极材料研究得最多的是贵金属 Pt[10 ,11] .贵金属 Pd对氧催化还原的研究工作很少 .我们首次…     

乙二胺功能化纤维素负载纳米钯催化Suzuki反应的研究

以氯化纤维素为原料, 通过与乙二胺的胺化反应制得乙二胺功能化纤维素(Cell-EDA), 然后再将胺化纤维素在氯化钯乙醇溶液中反应可以方便制备得到乙二胺功能化纤维素负载的纳米钯催化剂(Cell-EDA-Pd0). 用SEM, TEM等分析方法对所制备的催化剂进行了表征; TEM分析表明乙二胺功能化纤维素负载的纳米钯呈球形, 粒径在10～20 nm左右. 实验结果表明, Cell-EDA-Pd0催化剂对空气稳定, 无需在惰性气体的保护下就能有效地催化芳基硼酸与卤代芳烃的Suzuki交叉偶联反应, 催化剂易回和收重复使用, 催化剂重复使用6次催化活性没有明显降低.     

碳纳米管上原位沉积钯-钴-镍纳米颗粒及其对乙醇氧化的电活性

以水合肼为还原剂,在水和乙醇的混合溶液中制备多壁碳纳米管(MWCNT)负载的纳米镍(Ni/MWCNT)和纳米镍钴(Ni-Co/MWCNT)颗粒,然后将它们分别与氯化钯溶液反应,形成的钯纳米颗粒原位沉积在MWCNT表面,从而得到MWCNT负载的Pd-Ni/MWCNT和Pd-Ni-Co/MWCNT催化剂。SEM和TEM图像显示,MWCNT上的催化剂颗粒是由5~10 nm的小颗粒团聚而成的30~100 nm的大颗粒,三金属催化剂的粒径比双金属的粒径小,在MWCNT上的分散度更高。ICP和EDS分析显示,Pd直接还原并包覆在纳米镍和纳米镍钴表面;采用循环伏安和计时电流技术,研究了催化剂在碱性溶液中对乙醇氧化的电催化活性,结果表明,Pd-Ni-Co/MWCNT催化剂对乙醇氧化具有强的电催化活性,乙醇氧化对应的峰电流密度达101.8 mA·cm^-2,并且催化剂催化活性稳定。     

碳纳米管上原位沉积钯-钴-镍纳米颗粒及其对乙醇氧化的电活性

以水合肼为还原剂,在水和乙醇的混合溶液中制备多壁碳纳米管(MWCNT)负载的纳米镍(Ni/MWCNT)和纳米镍钴(Ni-Co/MWCNT)颗粒,然后将它们分别与氯化钯溶液反应,形成的钯纳米颗粒原位沉积在MWCNT表面,从而得到MWCNT负载的PdNi/MWCNT和Pd-Ni-Co/MWCNT催化剂。SEM和TEM图像显示,MWCNT上的催化剂颗粒是由5~10 nm的小颗粒团聚而成的30~100 nm的大颗粒,三金属催化剂的粒径比双金属的粒径小,在MWCNT上的分散度更高。ICP和EDS分析显示,Pd直接还原并包覆在纳米镍和纳米镍钴表面;采用循环伏安和计时电流技术,研究了催化剂在碱性溶液中对乙醇氧化的电催化活性,结果表明,Pd-Ni-Co/MWCNT催化剂对乙醇氧化具有强的电催化活性,乙醇氧化对应的峰电流密度达101.8 m A·cm~(-2),并且催化剂催化活性稳定。     

纳米丝负载钯催化剂的制备及催化烯烃加氢性能研究

利用电纺丝技术制备出苯乙烯-丙烯腈共聚物负载钯的纳米丝催化剂.对催化剂进行了SEM、TEM、IR和XPS的测试.所制备的催化剂对α-己烯催化氢化结果表明,该催化剂在常温、氢气常压下具有很高的催化活性和较好的重复使用性,并且催化氢化过程中存在烯烃的异构化反应.实验结果表明,反应时间为150min时纳米催化剂A对α-己烯催化加氢生成正己烷的转化率是传统催化剂PdCl2/-γAl2O3的4.7倍.     

Palladium-catalysed transfer hydrogenation of aromatic nitro compounds — an unusual chain elongation

Aromatic nitro compounds are reduced via transfer hydrogenation in the presence of palladium on magnesium-lanthanum mixed oxide support in ethanol yielding the corresponding amines. With several acetophenone derivatives, the reduction was accompanied by chain elongation whilst the carbonyl group remained intact.     

温控聚乙二醇两相体系中纳米钯催化肉桂醛选择性加氢反应

将具有“高温混溶、室温分相”功能的聚乙二醇4000(PEG₄₀₀₀)与甲苯-正庚烷组成的两相体系用于纳米钯催化的肉桂醛选择性加氢反应中.在优化的反应条件下,肉桂醛转化率和氢化肉桂醛选择性分别为99%和98%.钯纳米催化剂经简单分相即可与产物分离,且循环使用8次,其活性和选择性基本保持不变.     

Synthesis of azo compounds by nanosized iron-promoted reductive coupling of aromatic nitro compounds

Treatment of a variety of aromatic nitro compounds with the active-iron based reducing system composed of FeCl₂·4H₂O, an excess of lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 5 mol %) in THF at room temperature, led to the formation of the corresponding symmetrically substituted azo compounds in good yield, resulting from a reductive coupling process. Some other functionalities including carbonyl, halogen, amino and hydroxyl groups, demonstrated to be compatible with the reaction conditions, giving none reduced or coupled by-products. In all cases, the azo compounds formed have not experienced over-reduction to the corresponding hydrazo or amino derivatives even upon prolonged heating or using an excess of the reducing system.     

Magnetically recoverable supported ruthenium catalyst for hydrogenation of alkynes and transfer hydrogenation of carbonyl compounds

A ruthenium (Ru) catalyst supported on magnetic nanoparticles (NiFe₂O₄) has been successfully synthesized and used for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The catalyst shows excellent selectivity toward the desired products with very high yield even after five repeated uses.     

A modular design of metal catalysts for the transfer hydrogenation of aromatic ketones

The ability of transition metal catalysts to add or remove hydrogen from organic substrates by transfer hydrogenation is a valuable synthetic tool. Towards a series of novel metal complexes with a P―NH ligand, [Ph₂PNHCH₂―C₄H₃O] derived from furfurylamine were synthesized. Reaction of [Ph₂PNHCH₂―C₄H₃O] 1 with [Ru(η⁶‐p‐cymene)(μ‐Cl)Cl]₂, [Ru(η⁶‐benzene)(μ‐Cl)Cl]₂, [Rh(μ‐Cl)(cod)]₂ and [Ir(η⁵‐C₅Me₅)(μ‐Cl)Cl]₂ gave a range of new monodentate complexes [Ru(Ph₂PNHCH₂―C₄H₃O)(η⁶‐p‐cymene)Cl₂] 2 , [Ru(Ph₂PNHCH₂―C₄H₃O)(η⁶‐benzene)Cl₂] 3 , [Rh(Ph₂PNHCH₂‐C₄H₃O)(cod)Cl] 4 , and [Ir(Ph₂PNHCH₂‐C₄H₃0)(η⁵‐C₅Me₅)Cl₂] 5 , respectively. All new complexes were fully characterized by analytical and spectroscopic methods. ³¹P‐{¹H} NMR, distortionless enhancement by polarization transfer (DEPT) or ¹H‐¹³C heteronuclear correlation (HETCOR) experiments were used to confirm the spectral assignments. Following activation by KOH, compounds 1 , 2 , 3 , 4 catalyzed the transfer hydrogenation of acetophenone derivatives to 1‐phenylethanol derivatives in the presence of iso‐PrOH as the hydrogen source. Notably [Ru(Ph₂PNHCH₂‐C₄H₃O)(η⁶‐benzene)Cl₂] 3 acts as an excellent catalyst, giving the corresponding alcohols in 98–99% yield in 20 min at 82°C (time of flight ≤ 297 h^?1) for the transfer hydrogenation reaction in comparison to analogous rhodium or iridium complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

Readily available hydrogen bond catalysts for the asymmetric transfer hydrogenation of nitroolefins

This paper focuses on readily accessible thiourea hydrogen bond catalysts derived from amino acids, whose steric and electronic features are modulated by their degree of substitution at the carbinol carbon center. These catalysts were applied in the asymmetric transfer hydrogenation of nitroolefins furnishing the chiral products in up to 99% yield and 86% enantiomeric excess. The proposed catalyst's mode of action is supported by mechanistic investigations.     

Synthesis of carbon-supported Pd/SnO_2 catalyst for highly selective hydrogenation of 2,4-difluoronitrobenzene

Halogenated anilines have a wide range of applications in the production of pharmaceuticals and agrochemical substances, and thus it is of great importance to develop highly active and selective catalysts for the hydrogenation of halogenated nitrobenzenes. We approach this challenge by probing noble metal/non-noble metal oxide nanoparticles(NPs) catalysts. Carbon-supported Pd/SnO2catalysts were synthesized by the chemical reduction method, and their catalytic activity was evaluated by the hydrogenation reaction of 2,4-difluoronitrobenzene(DFNB) to the corresponding 2,4-difluoroaniline(DFAN), showing a remarkable synergistic effect of the Pd and SnO2 NPs. The as-prepared Pd/SnO2/C catalysts were characterized using TEM, XRD, H2 TPD and XPS techniques. Modifications to the electronic structure of the Pd atoms through the use of SnO2 led to the suppression of the hydrogenolysis of the C–F bond and the acceleration of nitrosobenzene(DFNSB) conversion and consequently, resulted in the inhibition of the formation of reactive by-products and may be responsible for the enhancements observed in selectivity.     

Ruthenium(II) complex catalysts bearing a pyridyl-supported pyrazolyl-imine ligand for transfer hydrogenation of ketones

A new class of hemilabile unsymmetrical 2-(1-arylimino)-6-(pyzazol-1-yl)pyridine ligands and their ruthenium(II) and nickel(II) NNN complexes were synthesized. The Ru(II) complex catalysts have been fully characterized and exhibited good to excellent catalytic activity in the transfer hydrogenation (TH) of ketones in refluxing 2-propanol. These results have demonstrated rare examples of active ruthenium(II) NNN complex catalysts that do not feature a N-H functionality for TH of ketones.     

Investigation into the enantioselection mechanism of ruthenium-arene-diamine transfer hydrogenation catalysts using fluorinated substrates

The effects of both steric and electronic properties of ketones on the selectivity in asymmetric transfer hydrogenation have been studied with aryl alkyl/fluoroalkyl ketones using four ruthenium based catalysts and two different media. The 1-arylethanones, 1-aryl-2-fluoroethanones and 2,2-difluoroacetophenones could be reduced with medium to high ee (86-99%), while the 1-aryl-2,2,2-trifluoroethanones were reduced with low selectivity in most systems. The change in enantioselectivity upon structural variation has been rationalised aided by regression analysis with substituent constants and the partial charge of the carbonyl carbon as predictors. The steric bulk of the alkyl/fluoroalkyl chain was found to be the major factor in determining selectivity in formic acid/triethylamine, while for reduction of a series of substituted 1-arylethanones and 1-aryl-2-fluoroethanones, the selectivity was found to depend on the electronic properties of the aromatic ring, supporting previous evidence that π-π interaction between the substrate and catalyst is important in determining the selectivity. For reductions in water using sodium formate as the hydrogen donor, altered and more complex selectivity mechanisms were observed. Experiments and regression focused on the variation of the alkyl/fluoroalkyl group of phenyl and 1-naphthyl ketones, showed that the selectivity correlated with the size of the substituent, but also the partial charge of the carbonyl carbon.     

Pd(OAc)2-catalyzed orthogonal synthesis of 2-hydroxybenzoates and substituted cyclohexanones from acyclic unsaturated 1,3-carbonyl compounds

A Pd-catalyzed orthogonal synthesis of substituted 2-hydroxybenzoates and substituted cyclohexanones was developed for the first time. The substituted 2-hydroxybenzoates were obtained from acyclic unsaturated 1,3-carbonyl compounds using a combination of catalytic Pd(OAc)₂ and Cu(OAc)₂. On the other hand, the substituted cyclohexanones were produced from similar substrates via catalytic Pd(OAc)₂ and hydrogen chloride. Each transformation was clean, easy to work up, provided the desired compounds in good purities, and did not require column chromatography purification.