Asymmetric hydrogenation of itaconic acid and enol acetate derivatives with the Rh-TangPhos catalyst

[reaction: see text] The Rh-TangPhos catalyst has been used for asymmetric hydrogenation of itaconic acid and enol acetate derivatives. A variety of chiral 2-substituted succinic acids and chiral acetates have been obtained in excellent ee values (up to 99% ee).     

Efficient rhodium-catalyzed asymmetric hydrogenation for the synthesis of a new class of N-aryl beta-amino acid derivatives

[reaction: see text] N-Aryl beta-amino esters were obtained by asymmetric hydrogenation of a new class of N-aryl beta-enamino esters. High conversions and up to 96.3% ee values were achieved with a Rh-TangPhos catalyst.     

First-Principles Microkinetic Study of Methanol Synthesis on Cu(221) and ZnCu(221) Surfaces

First-principle based microkinetic simulations are performed to investigate methanol synthesis from CO and CO₂ on Cu(221) and CuZn(221) surfaces. It is found that regardless of surface structure, the carbon consumption rate follows the order:CO hydrogenation > CO/CO₂ hydrogenation > CO₂ hydrogenation. The superior CO hydrogenation activity mainly arises from the lower barriers of elementary reactions than CO₂ hydrogenation. Compared to Cu(221), the introduction of Zn greatly lowers the activity of methanol synthesis, in particularly for CO hydrogenation. For a mixed CO/CO₂ hydrogenation, CO acts as the carbon source on Cu(221) while both CO and CO₂ contribute to carbon conversion on CuZn(221). The degree of rate control studies show that the key steps that determine the reaction activity of CO/CO₂ hydrogenation are HCO and HCOO hydrogenation on Cu(221), instead of HCOOH hydrogenation on CuZn(221). The present work highlights the effect of the Zn doping and feed gas composition on methanol synthesis.     

Ziegler-type hydrogenation catalysts made from group 8–10 transition metal precatalysts and AlR3 cocatalysts: A critical review of the literature

Ziegler-type hydrogenation catalysts (group 8–10 transition metal precatalysts plus AlR₃ cocatalysts) are one of the most important families of industrial hydrogenation catalysts, especially for polymer hydrogenation. Despite their ～40 year history of industrial use, there is a need for improved fundamental understanding in order to make further, rationally directed improvements in these catalysts. This review examines the existing literature on Ziegler-type hydrogenation catalysts, specifically: (i) the variables important to catalyst synthesis, (ii) the catalyst formation reaction mechanism, (iii) the compositional and structural nature of the active catalyst species, and (iv) the mechanism of catalytic hydrogenation. This review also (v) discusses the current approaches to the homogeneous versus heterogeneous catalysis question, with the goal of identifying if Ziegler-type hydrogenation catalysts are homogeneous (e.g., monometallic) versus heterogeneous (e.g., nanoclusters) as the true catalyst(s). A summary of the main insights from each section of the review is also given.     

Heterogeneous addition of H2 to double and triple bonds over supported Pd catalysts: a parahydrogen-induced polarization technique study

In this work, the contribution of the pairwise H(2) addition to the overall reaction mechanism was studied under the systematic variation of both the Pd particle size and the properties of the catalyst support using the hydrogenation of propene and propyne over supported Pd catalysts as representative examples. For Pd supported on alumina, silica and zirconia, only propene formed upon hydrogenation of propyne with para-H(2) exhibits hyperpolarization. In contrast, propane formed in hydrogenation of propyne or propene is not hyperpolarized. This demonstrates the existence of different routes of H(2) addition to double and triple bonds on supported Pd catalysts. The unique ability of Pd/TiO(2) catalysts to add H(2) in a pairwise manner not only to the triple but also to the double bond is demonstrated. This finding indicates that the Pd-support interaction is of primary importance in determining not only the magnitude of the hyperpolarization of the NMR lines of the reaction products but even the involvement of the pairwise H(2) addition and hence the mechanism of heterogeneous hydrogenation. The comparative analysis of the selectivities toward pairwise H(2) addition suggested the existence of different surface active sites responsible for all three reaction routes: the direct total hydrogenation of propyne into propane, its selective hydrogenation into propene, and hydrogenation of propene into propane. A reaction scheme which accounts for the formation of the observed hyperpolarized and non-polarized reaction products in propyne and propene hydrogenation with para-H(2) over supported Pd catalysts is suggested. For the first time, application of the PHIP technique allowed us to demonstrate that hydrogenation of propene does not take place in the presence of propyne on supported Pd catalysts.     

Preparation of Hydrogenated Nitrile Rubber

Hydrogenated nitrile rubber is an oil and solvent resistant rubber and particularly give more resistant to heat, ozone, light. It is generally prepared from nitrile rubber by selective hydrogenation using a suitable catalyst system. In the present work a prepared method was adapted for the hydrogenation reaction of nitrile rubber using homogeneous tris(tri-phenlphosphine)chlorhodium(I) catalyst (RhCl(PPh3)) system. The hydrogenation reaction was carriedout at different temperature, pressure, time and catalyst concentration, the concentration, the conditions of hydrogenation are stated in table 1.     

Captured at last: a catalyst-substrate adduct and a Rh-dihydride solvate in the asymmetric hydrogenation by a Rh-monophosphine catalyst

The mechanism of asymmetric hydrogenation catalyzed by [Rh(NBD)((R)-PhenylBinepine)(2)]SbF(6)1 has been studied by NMR experiments and DFT computations. Either the low-temperature hydrogenation of the catalyst-substrate adduct 4 or the reaction of solvate dihydride 6 with MAC produced the hydrogenation product with over 99% ee (S).     

Organometallic complexes in supported ionic-liquid phase (SILP) catalysts: a PHIP NMR spectroscopy study

para-Hydrogen induced polarization (PHIP) NMR spectroscopy emerges as an efficient and robust method for on-line monitoring of gas-phase hydrogenation reactions. Here we report detailed investigations of supported ionic liquid phase (SILP) catalysts in a continuous gas-phase hydrogenation of propene with PHIP NMR spectroscopy. A relocation of the rhodium complex in the thin layer of ionic liquid in the SILP catalyst at the initial stage of the propene hydrogenation is demonstrated. PHIP NMR spectroscopy can provide profound insight into the evolution of SILP catalysts during hydrogenation reactions.     

Ionic liquids for the sustainable transformation of levulinic acid to gamma-valerolactone (GVL)

This short review is focused on recent findings on the role of ionic liquids (ILs) in catalysing the hydrogenation of levulinic acid (LA) to gamma valerolactone (GVL), which is a cascade reaction involving more than one type of reaction. A brief introduction on green aspects of IL as a catalyst followed by various types of ILs being used for hydrogenation of LA to GVL are discussed. The unique characteristics of ILs responsible for hydrogenation reaction are also explained along with the current and upcoming scenario of IL catalysed hydrogenation of LA to GVL.     

Organic solvent‐free catalytic hydrogenation of diene‐based polymer nanoparticles in latex form. Part II. Kinetic analysis and mechanistic study

The central challenge that has limited the development of catalytic hydrogenation of diene‐based polymer latex (i.e., latex hydrogenation) in large‐scale production pertains to how to accomplish the optimal interplay of accelerating the hydrogenation rate, decreasing the required quantity of catalyst, and eliminating the need for an organic solvent. Here, we attempt to overcome this dilemma through decreasing the dimensions of the polymer substrate (such as below 20 nm) used in the hydrogenation process. Very small diene‐based polymer nanoparticles were synthesized and then used as the substrates for the subsequent latex hydrogenation. The effects of particle size, temperature, and catalyst concentration on the hydrogenation rate were fully investigated. An apparent first‐order kinetic model was proposed to describe the rate of hydrogen uptake with respect to the concentration of the olefinic substrate (C?C). Mass transfer of both the hydrogen and catalyst involved in this solid (polymer)–liquid (water)–gas (hydrogen) three‐phase latex system is discussed. The competitive coordination of the catalyst between the C?C and acrylonitrile units within the copolymer was elucidated. It was found that (1) using very small diene‐based polymer nanoparticles as the substrate, the hydrogenation rate of polymer latex can be increased vastly to achieve a high conversion of 95% while a quite low level of catalyst loading is required; (2) this latex hydrogenation process was completely free of organic solvent and no cross‐linking was found; (3) the mass transfer of hydrogen is not a rate‐determining step in the present hydrogenation reactions; (4) the catalyst was dispersed homogeneously within the polymer nanoparticles; (5) for the reaction that has reached about 95 mol % conversion, the kinetic study shows that the reaction is chemically controlled with an apparent activation energy of 100–110 kJ/mol; (6) the strong coordination of C[tbond]N to the catalytically active species RhH₂Cl(PPh₃)₂ imposed a negative effect on the hydrogenation activity. The present research provides a comprehensive study to appreciate the underlying chemistry of latex hydrogenation of diene‐based polymer nanoparticles and more importantly shows great promise toward the commercialization of a “green” catalytic hydrogenation operation of a diene‐based polymer latex in industry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

低温加氢催化剂的设计:理论与实践(英文)

简要总结了我们在C=C及C=O双键低温加氢双金属催化剂方面的最新研究成果.首先,我们以环己烯加氢为探针反应,证明了平行使用多种研究手段的重要性,包括单晶表面的基础研究与DFT计算,多晶表面的合成与表征,负载型催化剂的制备与性能测试等.其次,总结了双金属催化剂在其他加氢反应,如丙烯醛C=O双键的选择性加氢,苯的低温加氢,以及乙炔的选择性加氢等反应中的应用.最后,讨论了利用金属碳化物代替贵金属Pt以减少双金属催化剂中Pt用量的可能性.     

CATALYTIC PROPERTIES OF POLYMER-STABILIZED COLLOIDAL METAL NANOPARTICLES SYNTHESIZED BY MICROWAVE IRRADIATION

Catalytic properties of polymer-stabilized colloidal metal nanoparticles synthesized by microwave irradiation were studied in the selective hydrogenation of unsaturated aldehydes, o-chloronitrobenzene and the hydrogenation of alkenes. The results show that nanosized metal particles synthesized by microwave irradiation have similar catalytic performance in selective hydrogenation of unsaturated aldehydes, better selectivity to o-chloroaniline in hydrogenation of o-chloronitrobenzene and higher catalytic activities in hydrogenation of alkenes, compared with metal clusters prepared by conventional heating. The same apparent activation energy (Ea = 29 kJ mol^-1) for hydrogenation of 1-heptene catalyzed with platinum nanoparticles prepared by both heating modes implied that the reaction followed the same mechanism.     

Catalytic Hydrogenation over Palladium Complex of Molecular Complex of Poly(4-vinylpyridine) with Acetic Acid

The palladium complex of the molecular complex of poly(4-vinylpyridine)with acetic acid (PVP/HAc-Pd) was prepared.Its catalytic activity for the hydrogenation of nitrobenzene was found much higher than that of the corresponding palladium complex of poly(4-vinylpyridine).In the presence of a strong inorganic alkali.especially potassium hydroxide.the catalytic activity is greatly improved.The suitable hydrogenation condition for PVP/HAc-Pd is to use 0.1mol/L ethanol solution of potassium hydroxide as the hydrogenation medium and the hydrogenation is carried out at 45 ℃。     

A Novel Production of γ-Butyrolactone Catalyzed by Homogeneous Ruthenium Complexes

γ-Butyrolactone (hereafter abbreviated GBL) is produced by the two-stage hydrogenation of maleic anhydride(MAH) in the liquid phase: the hydrogenation of MAH to succinic anhydride(SAH) in the first stage and the subsequent hydrogenation of SAH to GBL in the second stage. A novel ruthenium catalyst system consisting of Ru salts, trialkylphosphine and p-toluene sulfonic acid (p-TsOH) was found very effective for the hydrogenation of SAH affording GBL, which exhibited excellent catalyst performance, exceeding 97% selectivity for GBL and high activity.     

Pt (111)面和Pt14团簇上肉桂醛吸附及选择性加氢机理研究

利用密度泛函理论研究了Pt（111）面及Pt₁₄团簇对肉桂醛（CAL）的吸附作用和不完全加氢的反应机理。分析吸附能结果表明,肉桂醛分子以C=O与C=C键协同吸附在Pt（111）面上的六角密积（Hcp）位最稳定,以C=C键吸附在Pt₁₄团簇上最稳定,且在Pt₁₄团簇上的吸附作用较Pt（111）面更强。由过渡态搜索并计算得到的反应能垒及反应热可知,肉桂醛在Pt（111）面和Pt₁₄团簇上均较容易对C=O键加氢得到肉桂醇（COL）。其中,优先加氢O原子为最佳反应路径,即Pt无论是平板还是团簇对肉桂醛加氢均有较好的选择性。同时发现,肉桂醛分子在Pt（111）面的加氢反应能垒较Pt₁₄团簇上更低,即Pt的催化活性及对肉桂醛加氢产物选择性与其结构密切相关,其中,Pt（111）面对生成肉桂醇更加有利。     

A highly selective arene hydrogenation catalyst that operates in ionic liquid

The synthesis and structural characterization of [Ru(eta(6)-p-cymene)(eta(2)-TRIPHOS)Cl][PF(6)] is described. The complex is a highly active, homogeneous arene hydrogenation catalyst that is selective toward the hydrogenation of aromatic rings in preference to alkenes, as demonstrated by the hydrogenation of allylbenzene to allylcyclohexane. The catalyst operates in both dichloromethane and ionic liquids and undergoes no decomposition in the latter solvent.     

Highly Enantioselective Hydrogenation of N‐Aryl Imines Derived from Acetophenones by Using Ru–Pybox Complexes under Hydrogenation or Transfer Hydrogenation Conditions in Isopropanol

The asymmetric reduction of N‐aryl imines derived from acetophenones by using Ru complexes bearing both a pybox (2,6‐bis(oxazoline)pyridine) and a monodentate phosphite ligand has been described. The catalysts show good activity with a diverse range of substrates, and deliver the amine products in very high levels of enantioselectivity (up to 99 %) under both hydrogenation and transfer hydrogenation conditions in isopropanol. From deuteration studies, a very different labeling is observed under hydrogenation and transfer hydrogenation conditions, which demonstrates the different nature of the hydrogen source in both reactions.     

丁二烯-b-甲基丙烯酸甲酯共聚物中C＝C的选择性催化加氢

以氯化三苯基膦铑为催化剂,对丁二烯-b-甲基丙烯酸甲酯共聚物的催化加氢反应进行了研究,用NMR、FTIR、动态粘弹谱和化学分析法对加氢产物进行了表征。证明RhCl[P(C₆H₅)₃]₃可有效地使共聚物中的C＝C加氢,且具有很高的选择性,未加氢的双键含量小于0.71%.     

非负载纳米多孔钯催化喹啉及其衍生物的化学选择性氢化反应:H_2分子异裂（英文）

纳米多孔金属是近十年发展起来的一类具有三维通孔结构的新型功能材料,其由纳米尺度的细孔和韧带构成,具有极大的比表面积;它还是一种无毒无载体的宏观材料,并且易制备、易回收和重复利用,因此作为高效的非均相催化剂已逐渐引起人们的重视.1,2,3,4-四氢喹啉是许多医药、农药、染料和天然产物的重要骨架.通过喹啉及其衍生物的选择性加氢反应制备1,2,3,4-四氢喹啉,具有原子利用率高和原料易得等优点.在过去,已经开发了许多类型的均相和非均相催化体系,并成功地用于催化喹啉及其衍生物的选择性加氢反应.尽管非均相催化体系具有诸多优点,但仍存在H_2压力(10–50 atm)和反应温度(60–150℃)相对较高的缺点.因此,开发更加温和条件下的喹啉及其衍生物的选择性加氢反应具有重要意义.此外,在喹啉及其衍生物的加氢反应过程中,H_2分子在非均相催化剂表面的裂解模式,即均裂还是异裂尚不清楚.因此,本文采用新型非均相催化剂纳米多孔钯,研究了喹啉及其衍生物的选择性加氢反应,在相对较低的H_2压力(2–5 atm)和温度(室温–50℃)下实现了目标反应,高收率、高选择性地得到1,2,3,4-四氢喹啉化合物.在最佳反应条件下,对底物的适用范围进行了考察.结果表明,各种含喹啉结构单元的化合物均能顺利发生反应,产物收率在62%–95%.而且该反应对甲基、甲氧基、羟基、酯基、醛基、酰胺基、卤素(F,Cl和Br)等官能团具有较好的兼容性.苯环上取代基的电子效应对反应有一定的影响,吸电子基有利于目标反应的进行.反应完成后,纳米多孔钯催化剂很容易回收,且循环使用多次后,仍未见催化活性降低.扫描电镜和透射电镜结果发现,循环使用后的纳米多孔钯催化剂结构没有发生明显改变,表明其结构稳定.浸出实验结果证明,没有钯原子浸出到反应液中,表明该纳米多孔钯催化反应属于多相催化过程.喹啉的选择性氢化反应被放大到克级的规模时,目标产物的收率仅略有降低,说明该方法具有很好的实用性.通过动力学实验发现,随着反应的进行,反应速率不断加快,表明反应过程中生成的乙胺和1,2,3,4-四氢喹啉同样扮演着路易斯碱性添加剂的角色,促进了反应的进行.通过反应机理研究,揭示了H–H键在纳米多孔钯表面发生了异裂,原位形成的Pd–H物种作为弱亲核试剂,对目标反应的选择性控制起到了至关重要的作用.     

贵金属催化p-叔丁基-α-甲基肉桂醛加氢

采用傅里叶变换红外光谱仪(FT-IR)、N₂吸脱附、X射线衍射(XRD)、透射电子显微镜(TEM)揭示了微波辅助-KOH处理对活性炭的物理化学性能的影响规律。 结果表明,活性炭表面的含氧基团的种类增加,微孔明显减少,中大孔的比例增大。 通过浸渍-原位还原方法制备了Pt、Pd、Ru、Rh负载微波辅助-KOH处理活性炭催化剂,并对其催化p-叔丁基-α-甲基肉桂醛选择性加氢性能进行了研究。 发现Pt具有优异的C=O加氢选择性,而Pd具有优良的C=C加氢选择性。 进一步研究了Pd-Pt双组分催化剂催化p-叔丁基-α-甲基肉桂醛加氢产物分布,随着Pt含量的增加, C=O选择性逐步提高, C=C选择性逐渐下降,且当m(Pd)∶m(Pt)=4∶1时,其催化剂的催化性能最佳。