Metal-based Heterogeneous Catalysts for One-Pot Synthesis of Secondary Anilines from Nitroarenes and Aldehydes

Recently, N-substituted anilines have been the object of increasing research interest in the field of organic chemistry due to their role as key intermediates for the synthesis of important compounds such as polymers, dyes, drugs, agrochemicals and pharmaceutical products. Among the various methods reported in literature for the formation of C–N bonds to access secondary anilines, the one-pot reductive amination of aldehydes with nitroarenes is the most interesting procedure, because it allows to obtain diverse N-substituted aryl amines by simple reduction of nitro compounds followed by condensation with aldehydes and subsequent reduction of the imine intermediates. These kinds of tandem reactions are generally catalyzed by transition metal-based catalysts, mainly potentially reusable metal nanoparticles. The rapid growth in the last years in the field of metal-based heterogeneous catalysts for the one-pot reductive amination of aldehydes with nitroarenes demands for a review on the state of the art with a special emphasis on the different kinds of metals used as catalysts and their recyclability features.     

钌催化芳香硝基化合物和脂肪三级胺反应一锅法合成喹啉衍生物

以芳香硝基化合物和脂肪三级胺为原料,三环己基膦四氟硼酸盐为配体,在三氯化钌催化下"一锅法"合成了一系列喹啉衍生物.该法不需要添加任何额外的还原剂,原料便宜易得,操作工艺简单,产率中等.产物结构通过IR,1H NMR,13C NMR,MS以及元素分析表征.     

负载Pd密偶催化剂的载体效应

采用尿素水解法或吸附沉淀法制备了金属氧化物载体,并用浸渍法负载0.5%Pd制得了Pd/Sn0.4Zr0.6O2,Pd/ZrO2,Pd/SnO2,Pd/SnO2-Al2O3和Pd/Al2O3催化剂.采用原位漫反射红外光谱、拉曼光谱、X射线光电子能谱和程序升温还原等方法对催化剂结构进行了表征,探讨了不同载体对表面PdOx物种化学吸附性质和氧化还原性能的影响,并与样品的丙烷氧化活性相关联.漫反射红外光谱表明,在Pd/SnO2-Al2O3中,Sn对Al2O3表面的Pd原子簇起到稀释作用,促进了Pd的分散,使得其CO线式吸附强度明显高于Pd/Al2O3,但Pd过高的分散度不仅减少了表面Pd-PdO活性位对的数目,而且使反应中间物种Pd-OH之间脱水困难,因而阻塞了活性位,降低了其循环氧化还原活性;而在Sn0.4Zr0.6O2复合氧化物载体中,SnO2有效地阻止了四方晶相ZrO2向稳态单斜晶相转变,且复合载体的比表面积较ZrO2和SnO2有所增加,其表面PdOx物种的分散度适中.此外,Sn0.4Zr0.6O2复合氧化物负载的Pd的价态介于Pd0与Pd2 之间,表面氧空位较多,促进了丙烷中C-H键的活化,使比表面积较低的Pd/Sn0.4Zr0.6O2具有最好的催化丙烷氧化能力,相反比表面积较高的Pd/SnO2-Al2O3活性很差,说明分散度适中且具有较低氧化态的PdOx(0相似文献   

膜反应器中Ni-Cu催化剂上CO加氢合成乙烯的研究

 将硅藻土－TiO2－聚乙烯（或聚丙烯）疏水复合膜反应器应用于\r\nCO加氢合成乙烯的反应过程，以Ni－Cu／TiSiO和Ni－Cu／MgSiO为催化\r\n剂，考察了反应温度、空速和进料组成等因素对CO转化率和乙烯选择性\r\n的影响．结果表明：膜催化反应的产物与常规催化反应相同，催化反应\r\n机理没有区别，在适宜条件下，膜催化反应的CO转化率和乙烯选择性较\r\n之常规催化反应提高了10％左右，二氧化碳和甲烷的选择性降低，而乙\r\n烷的选择性略有增加．     

A Reusable Co Catalyst for the Selective Hydrogenation of Functionalized Nitroarenes and the Direct Synthesis of Imines and Benzimidazoles from Nitroarenes and Aldehydes

The use of abundantly available transition metals in reactions that have been preferentially mediated by rare noble metals, for example, hydrogenations, is a desirable aim in catalysis and an attractive strategy for element conservation. The observation of novel selectivity patterns with such inexpensive metal catalysts is especially appealing. Herein, we report a novel, robust, and reusable cobalt catalyst that permits the selective hydrogenation of nitroarenes in the presence of highly hydrogenation‐sensitive functional groups, as well as the direct synthesis of imines from nitroarenes and aldehydes or ketones in the presence of such substituents. Furthermore, we introduce the first base‐metal‐mediated direct synthesis of benzimidazoles from nitroarenes and aldehydes. Functional groups that are easy to hydrogenate are again well tolerated.     

Amino-Modified Silica-Supported Copper-Palladium Alloy. Synthesis and Use in Selective Hydrogenation of Disubstituted Nitroarenes in a Flow Micro Reactor

Russian Journal of Organic Chemistry - A copper-palladium catalyst supported on amino-modified silica has been synthesized by chemical reduction. It has been found that submicron particles of a...     

载体对负载PdO催化剂的CO氧化活性的影响

由于催化燃烧比传统的热力燃烧法有反应温度低和能量消耗低的优点，因而广泛用于挥发性有机物和CO的消除．把和铂是最常用的催化剂，但是载体对催化性能的影响很大【‘’‘］．本文制备了系列负载把催化剂，发现载体的性质对催化剂的CO氧化活性影响很大．本文所用载体为CeO。，TIO。，SnO。，AI。O。，ZAI。，ZSM－5和SIO。催化剂制备采用浸渍法，把负载量为5％（质量分数）．催化剂经120C烘干后，于650’C空气气氛焙烧4h制成．在常压固定床流动反应装置上考察催化剂的CO氧化活性，反应气组成为CO2．4％，O。1．2％，N。96．4…     

载体对负载型金催化剂上甲醛催化氧化的影响

采用沉积.沉淀法和氨水络合法制备了Al2O3,TiO2,CeO2和SiO2负载的纳米金催化剂,利用元素分析、x射线衍射、氮气物理吸附、程序升温还原、透射电镜和拉曼光谱等技术对催化剂进行了表征,并考察了其低温催化甲醛氧化活性.结果表明,Au/CeO2的催化性能最佳,在40℃时甲醛转化率仍能保持在80%以上.催化剂的活性同时受Au的化学状态和载体性质的影响.Au/CeO2催化剂较高的低温活性可能与离子态的Au物种有关,同时AuxCe1-xO2-δ固溶体的形成产生了大量的氧缺位,提高了氧的活化能力,也有助于提高催化剂的低温活性.     

A One-Pot Selective Synthesis of N-Boc Protected Secondary Amines: Tandem Direct Reductive Amination/N-Boc Protection

A one-pot tandem direct reductive amination of aldehydes with primary amines resulting in N-Boc secondary amines using a (Boc)(2)O/sodium triacetoxyborohydride (STAB) system is reported. The tandem procedure is efficient, selective, and versatile, giving excellent yields of N-Boc protected secondary amines even in those cases where the products are prone to intramolecular lactamization.     

Towards Atomically Precise Supported Catalysts from Monolayer-Protected Clusters: The Critical Role of the Support

Controlling the size and uniformity of metal clusters with atomic precision is essential for fine-tuning their catalytic properties, however for clusters deposited on supports, such control is challenging. Here, by combining X-ray absorption spectroscopy and density functional theory calculations, it is shown that supports play a crucial role in the evolution of monolayer-protected clusters into catalysts. Based on the acidic nature of the support, cluster-support interactions lead either to fragmentation of the cluster into isolated Au–ligand species or ligand-free metallic Au⁰ clusters. On Lewis acidic supports that bind metals strongly, the latter transformation occurs while preserving the original size of the metal cluster, as demonstrated for various Au_n sizes. These findings underline the role of the support in the design of supported catalysts and represent an important step toward the synthesis of atomically precise supported nanomaterials with tailored physico-chemical properties.     

负载型MgO催化苯乙酮Meerwein-Ponndorf-Verley反应中的载体效应

通过浸渍法制备活性炭(AC)、全硅介孔分子筛MCM-41、硅胶(SiO₂)、γ-Al₂O₃等四种载体负载的MgO催化剂, 考察其在以异丙醇为氢源的苯乙酮Meerwein-Ponndorf-Verley (MPV)反应中的催化活性, 并和纯MgO进行对比研究, 同时对样品进行XRD、TEM、N₂吸附-脱附、XPS及CO₂-TPD等表征分析, 研究载体效应对催化剂活性的影响. 结果表明: 纯MgO因其比表面积较小, 表面暴露的碱中心数目较少, 其活性较低. 10% MgO/AC中MgO具有良好的分散性, 且与AC载体不发生强相互作用, MgO以小晶粒形式存在于载体表面, 致使催化剂表面的碱中心数目显著提高|另外, 苯乙酮上苯环π电子与AC载体中石墨层π电子可能存在相互作用, 致使催化剂活性中心附近的苯乙酮浓度增大|上述两方面原因使该催化剂具有良好的活性. 而在10% MgO/MCM-41, 10% MgO/SiO₂, 10% MgO/γ-Al₂O₃中, 载体均与MgO发生强相互作用, 使得其碱中心数目急剧下降, 导致其催化活性不明显.     

负载型ZrO2催化苯甲醛Meerwein-Ponndorf-Verley反应中的载体效应（英文）

采用浸渍法制备了Si-MCM-41和Al-MCM-41(Si/Al=50)介孔分子筛,SiO2,γ-Al2O3及MgO等负载的ZrO2催化剂,考察了其在以异丙醇为氢源苯甲醛Meerwein-Ponndorf-Verley(MPV)还原反应中的催化活性,并与纯ZrO2的催化活性进行对比.同时,采用X射线衍射、N2吸脱附法、X射线光电子能谱、紫外-可见漫反射光谱和吡啶原位吸附红外光谱等手段表征了催化剂.结果表明,ZrO2负载于Si-MCM-41,Al-MCM-41和SiO2后,催化活性明显提高,这归因于ZrO2与载体间存在强相互作用形成ZrOSi键,使催化剂表面ZrOH数量显著增多,Lewis酸中心强度增强,并出现Brnsted酸中心,三种催化剂的活性高低次序是5%ZrO2/Si-MCM-41>5%ZrO2/Al-MCM-41>5%ZrO2/SiO2.而5%ZrO2/Al2O3和5%ZrO2/MgO基本无催化活性,可归因为ZrO2与γ-Al2O3的弱相互作用使5%ZrO2/Al2O3的酸性与γ-Al2O3类似,ZrO2与MgO的强相互作用使5%ZrO2/MgO基本无酸性.     

担载铜镍催化剂氢溢流现象的TPR研究

本文采用TPR(Temperature Programmed Reduction)作为主要表征手段,对担载铜、镍催化剂循环还原-氧化(RedoX过程)处理前后的样品进行了表征.其次也进行了TPR测试后所得金属铜(镍)催化剂催化还原其前体氧化物(auto-catalysed reduction)的研究.发现这两种研究方式所得种种有趣结果都可归属于氢溢流现象.RedoX处理后,其TPR谱上金属氧化物的还原峰向低温区位移,并伴有总耗氢量的增加.其中峰位移可归属于Redox过程未被氧化完全的还原态金属(特别是铜)离解氢分子,形成的氢原子溢向邻近的金属氧化物(如CuO),使其在较低温度下还原;而耗氢量的增加则可归属氢原子向载体(SiO_2或Al_2O_3)的溢流,载体被活化使总耗氢量增加.上述现象可认为是同一颗粒间的氢溢流.在自催化还原过程中出现的氢溢流现象(低温区出现新还原峰和总耗氢量增加)可认为是催化剂不同颗粒间的氢溢流.总之TPR可以作为研究同一颗粒和不同颗粒间发生氢溢流行之有效的方法.     

负载型Cu-Mn-Ce催化剂燃烧VOCs反应的载体效应

以MgO,Al2O3,SiO2,TiO2和ZrO2为载体,采用浸渍法制备了负载型Cu-Mn-Ce(CMC)三元复合氧化物催化剂,并用TG,XRD,BET和H2-TPR对催化剂进行了表征,以甲苯和丙酮催化燃烧为模型反应,考察了该催化剂的催化活性。结果表明,纯CMC催化剂的铈基固溶体结构表现出优良的催化活性,当CMC负载在SiO2和Al2O3上后,其大比表面积和表面羟基均不利于CMC活性固溶体结构的形成,另外Mn,Cu等过渡金属与MgO载体发生相互作用而破坏了CMC的活性结构。TiO2和ZrO2则较好地保持了CMC活性固溶体的结构,并显著提高了CMC催化剂的高温热稳定性。     

二氧化硅担载铜系催化剂上异丁烯与甲醛缩合一步生成异戊二烯的研究

本文对前文所表征过的5个Cu/SiO_2催化剂进行了烯醛缩合反应制异戊二烯的活性评价.并对其反应后未再生的样品进行了XRD及XPS表征,关联表征与反应结果发现这些纯铜系催化剂上存在的两种铜组分(CuO和孤立Cu~(2+)),可被反应物甲醛还原为金属铜或Cu_2O.从反应初始活性数据来看,似乎可以认为Cu_2O是烯醛反应的活性相之一,且很可能是活化甲醛的中心.而金属铜则对生成异戊二烯不起活性作用.Cu_2O所起的可能是一种弱酸弱碱双功能位的作用.文中还对具有较长寿命的N-115(二氧化硅担载铜锑催化剂)和N-218(二氧化硅担载铜系催化剂)二催化剂寿命试验前后的活性数据进行了对比,并从酸碱催化的角度推论了影响铜系催化剂寿命的两个可能因素.     

Zinc Borohydride-Ionic Liquid： Stable and Efficient System for Reductive Reaction of Aldehydes with Primary Amines to Corresponding Secondary Amines

Ionic liquids（ILs） are attracting much attention in various fields of chemical synthesis, electrochemical applications, liquid-liquid extractions, as well as biotransformations. Among those fields, the application of ILs as the potential green solvent for a wide variety of synthetic processes is an area of intense researches. High yield, high selectivity, and good catalytic charac-teristics have usually been achieved. After the isolation of products, ILs can usually be recovered and recycled many times by simple treating procedures, such as, filtration, extraction, and dryness.     

负载Rh催化剂上CO加H2制C2含氧化合物及助剂（载体）作用

石油资源的紧缺, 使得基于利用煤和天然气生产液体燃料及有机化工产品的C1化学得到迅速发展 . 从目前的技术水平看, 煤、天然气的间接转化路线最具应用前景, 即首先将天然气、煤转化为合成气, 然后由合成气来生产化工产品及液体燃料. 除费用高昂的合成气造气过程外, 制约煤、天然气间接利用路线的另一关键因素, 是由合成气出发只能制得有限的几种产物, 远不足于建立起替代以石油为原料的生产路线, 因此, 开展合成气多种转化途径的研究具有重要的现实意义.