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1.
Christopher J. Baddeley Timothy E. Jones Aoife G. Trant Karen E. Wilson 《Topics in Catalysis》2011,54(19-20):1348-1356
Enantioselective catalysis is an increasingly important method of providing enantiomeric compounds for the pharmaceutical and agrochemical industries. To date, heterogeneous catalysts have failed to match the industrial impact achieved by homogeneous systems. One successful approach to the creation of heterogeneous enantioselective catalysts has involved the modification of conventional metal particle catalysts by the adsorption of chiral molecules. This article examines the contribution of effects such as chiral recognition and amplification to these types of system and how insight provided by surface science model studies may be exploited in the design of more effective catalysts. 相似文献
2.
Formic acid and formates are often produced by hydrogenation of CO2 with hydrogen over homogeneous catalysts. The present review reports recent achievements in utilization of heterogeneous catalysts. It shows that highly dispersed supported metal catalysts are able to carry out this reaction by providing activation of hydrogen on the metal sites and activation of CO2 or bicarbonate on the support sites. Important advances have recently been achieved through utilization of catalysts using CxNy materials as supports. The high activity of these catalysts could be assigned to their ability to stabilize the active metal in a state of single-metal atoms or heterogenized metal complexes, which may demonstrate a higher activity than metal atoms on the surface of metal nanoparticles. 相似文献
3.
4.
Dendrimers, well-defined hyper-branched macromolecules with characteristic globular structures, have inspired chemists and
chemical engineers to develop new materials and several applications have been explored. The dendritic molecule has emerged
as an attractive material in the field of catalysis and various dendrimer catalysts have been applied not only to catalytic
reactions but also to non-catalytic ones such as nanoscale reactor systems. This article presents a review of research work
on the dendrimer-based catalysis involving the rational design of homogeneous or heterogeneous chiral dendrimer catalysts
for enantioselective reactions and the synthesis of catalytically active bimetallic nanoparticles in the presence of dendrimer
as a template.
This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University. 相似文献
5.
Katalin Balázsik György Szőllősi Ottó Berkesi Gábor Szalontai Ferenc Fülöp Mihály Bartók 《Topics in Catalysis》2012,55(11-13):880-888
The preparation and application of heterogeneous chiral catalysts are described. Heterogeneous Pd, Ir and Ru catalysts were tested in the enantioselective hydrogenations of N-heterocyclic compounds, namely 6,7-dimethoxy-3,4-dihydroisoquinoline and 1-methylene-2-ethoxycarbonyl-6,7-dimetoxy-3,4-dihydroisoquinoline in the presence of optically pure cinchonidine, (S,S)- and (R,R)-Ts-DPEN ligands. Cinchonidine-modified metal catalysts exhibited low ee, whereas catalysts stabilized by triphenylphosphane and modified by (S,S)-Ts-DPEN afforded promising ee values (70–80 %). Immobilized Ru(II)-aminophosphane complexes were found to be active in these hydrogenations producing the corresponding tetrahydroisoquinoline derivatives in high optical purities (up to 97 %). The latter catalysts were characterized by infrared spectroscopy, solid-state MAS NMR spectroscopy and elemental analysis. Recycling of these catalysts showed constant or increasing activities in racemic hydrogenation, whereas the presence of the chiral ligands led to leaching of the active species in the liquid phase. 相似文献
6.
Two chiral manganese(III) salen catalysts, bearing different chiral diamine bridges, were anchored by direct axial coordination of the metal centre onto the phenolate groups of a modified commercial activated carbon. The modification of the activated carbon was achieved by reaction between sodium hydroxide and surface phenol groups giving rise to phenolate groups (CoxONa), which were characterised by XPS, TG and TG-IR. Characterisation of immobilised manganese(III) salen catalysts onto CoxONa material by XPS, ICP-AES and TG-IR clearly point to reaction between carbon surface phenolate groups and the manganese(III) complexes through axial coordination of the metal centre to these groups.These materials were active and enantioselective in the epoxidation of styrene and α-methylstyrene in dichloromethane at 0 °C using, respectively, m-CPBA/NMO and NaOCl. Only for α-methylstyrene comparable asymmetric inductions were found in the epoxide as the homogeneous phase reactions and catalyst reuse led to no significant loss of catalytic activity and enantioselectivity. 相似文献
7.
Ketone-catalyzed asymmetric epoxidation reactions 总被引:1,自引:0,他引:1
Yang D 《Accounts of chemical research》2004,37(8):497-505
This Account summarizes our efforts in developing organic ketone catalysts for enantioselective and diastereoselective epoxidation of olefins. We have developed an efficient and general protocol for epoxidation of olefins using dioxiranes generated in situ from activated ketones and Oxone (2KHSO5.KHSO4.K2SO4) in a homogeneous aqueous solvent system. We have also developed chiral ketone catalysts for highly enantioselective epoxidation of unfunctionalized trans-olefins and trisubstituted olefins. Excellent diastereoselectivities have been achieved for epoxidation of substituted cyclohexenes with ketone catalysts. 相似文献
8.
Genet JP 《Accounts of chemical research》2003,36(12):908-918
This Account covers the design of Ru catalysts and ligands. Two classes of chiral phosphine ligands are prepared: the electron-rich trans-2,4-substituted phosphetanes, readily available from optically pure 1,3-diol cyclic sulfates, and atropoisomeric ligands (SYNPHOS, MeO-NAPhePHOS, bearing heterotopic biaryl moieties, and a chiral water-soluble diguanidinium binaphthyl diphosphine, Digm-BINAP). Applications of these ligands to rhodium- and ruthenium-mediated hydrogenation of ketones and olefins have been reported with high enantioselectivities. The recognition abilities of Ru-SYNPHOS for a wide range of ketones is superior to those observed with BINAP, MeO-NAPhePHOS, and MeO-BIPHEP. Several biologically active compounds have been prepared through dynamic kinetic resolution. This work gives access to a number of highly active catalysts of the type [Ru(biphosphane)(H)(eta(6)-cot)]BF(4). These catalysts have demonstrated their utility in the enantioselective hydrogenation of the tetrasubstituted cyclopentenone "dehydrodione", which leads to the commercially important perfume component Paradisone (Firmenich). 相似文献
9.
Jian-Hua Zhou Ya-Jun Ji Wang-Juan Dang Xiao-Lei Liu Gui-Wang Zhao Chuan-Xiang Zhang Ji-Shuang Zhao Qing-Bin Fu Huo-Ping Hu 《Electrochimica acta》2007,52(14):4691-4695
Mesoporous carbon with ordered hexagonal structure derived from the co-assembly of triblock copolymer F127 and resol was employed as the carbon support of Pt catalysts for hydrogen electro-oxidation. Structural characterizations revealed that the mesoporous carbon exhibited large surface area and uniform mesopores. The Pt nanoparticles supported on the novel mesoporous carbon were fabricated by a facile CTAB assisted microwave synthesis process, wherein CTAB was expected to improve the wettability of carbon support as well as the dispersion of Pt nanoparticles. X-ray diffraction and transmission electron microscopy were applied to characterize the Pt catalysts. It was found that the Pt nanoparticles were uniform in size and highly dispersed on the mesoporous carbon supports. The cyclic voltammograms in sulfuric acid demonstrated that the electrochemical active surface area of Pt catalysts prepared with CTAB was two times than that without CTAB. 相似文献
10.
Carbon-heteroatom bonds (C-X) are ubiquitous and are among the most reactive components of organic compounds. Therefore investigations of the construction of C-X bonds are fundamental and vibrant fields in organic chemistry. Transition-metal-catalyzed heteroatom-hydrogen bond (X-H) insertions via a metal carbene or carbenoid intermediate represent one of the most efficient approaches to form C-X bonds. Because of the availability of substrates, neutral and mild reaction conditions, and high reactivity of these transformations, researchers have widely applied transition-metal-catalyzed X-H insertions in organic synthesis. Researchers have developed a variety of rhodium-catalyzed asymmetric C-H insertion reactions with high to excellent enantioselectivities for a wide range of substrates. However, at the time that we launched our research, very few highly enantioselective X-H insertions had been documented primarily because of a lack of efficient chiral catalysts and indistinct insertion mechanisms. In this Account, we describe our recent studies of copper- and iron-catalyzed asymmetric X-H insertion reactions by using chiral spiro-bisoxazoline and diimine ligands. The copper complexes of chiral spiro-bisoxazoline ligands proved to be highly enantioselective catalysts for N-H insertions of α-diazoesters into anilines, O-H insertions of α-diazoesters into phenols and water, O-H insertions of α-diazophosphonates into alcohols, and S-H insertions of α-diazoesters into mercaptans. The iron complexes of chiral spiro-bisoxazoline ligands afforded the O-H insertion of α-diazoesters into alcohols and water with unprecedented enantioselectivities. The copper complexes of chiral spiro-diimine ligands exhibited excellent reactivity and enantioselectivity in the Si-H insertion of α-diazoacetates into a wide range of silanes. These transition-metal-catalyzed X-H insertions have many potential applications in organic synthesis because the insertion products, including chiral α-aminoesters, α-hydroxyesters, α-hydroxyphosphonates, α-mercaptoesters, and α-silyl esters, are important building blocks for the synthesis of biologically active compounds. The electronic properties of α-diazoesters and anilines markedly affected the enantioselectivity of N-H insertion reaction, which supports a stepwise ylide insertion mechanism. A novel binuclear spiro copper complex was isolated and fully characterized using X-ray diffraction analysis and ESI-MS analysis. The positive nonlinear effect indicated that binuclear copper complexes were the catalytically active species. The 14-electron copper centers, trans coordination model, perfect C(2)-symmetric chiral pocket, and Cu-Cu interaction facilitate the performance of the chiral spiro catalysts in X-H insertion reactions. 相似文献
11.
Nickel compounds were deposited on alumina-silica ceramic foam by different methods, in particular a homogeneous precipitation and a heterogeneous sol-gel processing to prepare catalyst for pyrolysis of alkanes (methane, propane-butane). Carbon deposits, in particular catalytic filamentous carbon (CFC) were synthesized on the Al/Si surface during the catalytic pyrolysis. Comparative analysis of the textural parameters of the initial support and composite carbon-mineral adsorbents was carried out. The effect of the method of catalyst preparation upon the morphology of supported nickel compounds and synthesized carbon deposits was examined in scanning electron microscope. The carbon yield for catalysts prepared by homogeneous precipitation was shown to be an order of magnitude higher than for the catalysts prepared by other methods. A uniform distribution of nickel nanoparticles deposited on the Al/Si foam by homogeneous precipitation led to the formation of a mesoporous CFC-layer with thickness of 0.5-2.0 μm and specific surface area ca. 500 m2/g due to chaotic interlacing of carbon nanofibers with a diameter of 50-100 nm and length exceeding 1 μm. 相似文献
12.
Dae-Woon Park Sung-Dae Choi Soon-Ja Choi Chung-Young Lee Geon-Joong Kim 《Catalysis Letters》2002,78(1-4):145-151
Organosilane-modified mesoporous materials have been prepared under mild and acidic conditions by a solvent evaporation method using C16TMABr surfactant as a template. The mesoporous samples synthesized in ethanol solvent by using this evaporation method showed a fully disordered pore system, but those obtained under hydrothermal conditions had highly ordered pores. The chiral salen Mn(III) complexes were immobilized on these organosilane-functionalized mesoporous silicas by a grafting method. The catalysts used in the asymmetric epoxidation of styrene and cis-stilbene and the effect of different mesoporous structures on the reactivity was investigated. Similar enantioselectivities were observed by using these heterogenized salen complexes as compared with reaction under homogeneous conditions. 相似文献
13.
Bu‐Mahn Park Soungyun Mun Jaesook Yun 《Advanced Synthesis \u0026amp; Catalysis》2006,348(9):1029-1032
The highly enantioselective reduction of imines is achieved by employing chiral Zn/diamine catalysts. This new catalytic protocol offers attractive features such as use of a non‐precious metal and an inexpensive silane, easy modification of chiral diamine ligands and provides ready access to chiral amines in good yields and with excellent enantioselectivities. 相似文献
14.
15.
Xinyuan Fan Sonia Sayalero Miquel A. Perics 《Advanced Synthesis \u0026amp; Catalysis》2012,354(16):2971-2976
Polystyrene (PS)‐supported diphenylprolinol silyl ethers have been developed as highly active catalysts for the enantioselective α‐amination of aldehydes. Understanding the mechanism of catalyst deactivation has led to the development of reaction conditions notably extending catalyst life in repeated recycling (10 cycles; accumulated TON of 480) and has allowed the implementation of a continuous flow α‐amination process (6 min residence time, 8 h operation). 相似文献
16.
Christopher W. Jones 《Topics in Catalysis》2010,53(13-14):942-952
Research on heterogenized metal complex catalysts has been carried out for 40 years. Despite thousands of published catalysts, there are only two significant commercial processes that utilize supported metal complex catalysts. Most academic papers are simply “demonstration of concept” studies reporting myriad ways to support various metal complex catalysts. Too few papers focus on rigorous studies of reaction kinetics, catalyst recycle, catalyst stability and deactivation pathways. Here, preliminary stability and deactivation studies of supported enantioselective Co-salen epoxide ring-opening catalysts and enantioselective Ru-salen olefin cyclopropanation catalysts are summarized. Insights with regard to catalyst deactivation suggest methodologies for catalyst stabilization, allowing for more effective catalyst recycle and enhanced catalyst turnover. Further examples where supported metal complex catalysts are applied in commercial processes will require the field to shift focus from “demonstration of concept” studies to more detailed investigations of catalyst stability and recyclability. 相似文献
17.
Homogeneous and heterogeneous catalysis have developed independently as two separate disciplines. Homogeneous catalysis is characterized by the use of highly active, well-characterized compounds. In contrast, heterogeneous catalysis exhibits the advantage of easy separation of the catalyst from the products and can be easily adapted to continuous flow processes. In recent years, there is an emerging trend in catalysis that is bridging these two fields. On one hand, some of the complexes used in homogeneous catalysis are really precursors of nanoparticles that are species that have been traditionally subject of study in heterogeneous catalysis. On the other hand, the use of novel media allows the recovery and reuse of homogeneous catalysts, a hallmark of heterogeneous catalysis. Also, powerful experimental techniques can characterize the active sites in solids up to a much higher level of detail. In this review, we have selected two reaction types that are attracting much current interest, namely the enantioselective addition to aldehydes by chiral metallosalen complexes and the palladium catalyzed C–C cross coupling, and used them to illustrate a series of strategies based on new concepts that can serve to impart the advantages of homogeneous catalysis into heterogeneous catalysis and vice versa. 相似文献
18.
综述了固体酸、固体碱和金属配合物在动态动力学拆分制备光学纯手性化合物进行外消旋化的催化机理,讨论了均相外消旋催化剂和多相外消旋催化剂在动态动力学拆分工艺中的应用,重点介绍了过渡金属配合物催化剂和生物酶配伍进行动态动力学拆分制备手性化合物的研究进展和发展趋势。 相似文献
19.
Sang Hoon Joo Dae Jong You Hyung Ik Lee Hyuk Chang Doyoung Seung 《Electrochimica acta》2006,52(4):1618-1626
This paper presents the effect of graphitic character of ordered mesoporous carbons (OMCs) on the performances of OMC supported catalysts for direct methanol fuel cells (DMFC). Two OMC samples with hexagonal mesostructure were prepared from phenanthrene and sucrose by nano-replication method using mesoporous silica as a template. Structural characterizations revealed that both OMCs exhibited large BET surface area and uniform mesopores, while the OMC synthesized from phenanthrene exhibited lower sheet resistance than the OMC derived from sucrose. The Pt nanoparticles were supported on both OMCs with very high dispersion, as the particle size was estimated under 3 nm despite high metal loading of 60 wt.%. In DMFC single cell test, the OMC supported Pt catalysts exhibited much higher performance than the commercial catalyst, which may be attributed to the high surface area and uniform mesopore networks of OMC. In particular, it was found that the performance of OMC supported catalysts can be significantly enhanced by lowering the resistance of OMC. 相似文献
20.
A series of bis(imino)pyridyl Co(II) and Fe(II) complexes containing allyloxy group on the pyridine ring were prepared. These metal complexes were heterogenized covalently immobilizing on modified SBA-15 mesoporous material in the presence of Karstedt catalyst. This immobilization technique was demonstrated to be an ideal one since the resulting supported catalysts resembled closely their homogeneous counterparts, mirroring the feature of active sites. 相似文献