Bulky Achiral Triarylphosphines Mimic BINAP in Ru(II)‐ Catalyzed Asymmetric Hydrogenation of Ketones

In the present work, we report on catalysis of the enantioselective hydrogenation of ketones with Ru(II) complexes composed of cheap achiral monodentate phosphine ligands in combination with an enantiopure 1,2‐diamine, affording a variety of optically active secondary alcohols with high efficiency and enantioselectivity. The steric impact of achiral monophosphine ligands in Ru complexes was found to be a critical factor for the high enantioselectivity of the reaction. This finding throws some light on a long‐standing challenge, the high cost of chiral bisphosphine ligands, associated with an industrial application of the asymmetric hydrogenation of ketones.     

Dendronized Poly(Ru‐BINAP) Complexes: Highly Effective and Easily Recyclable Catalysts For Asymmetric Hydrogenation

A new kind of dendronized polymeric chiral BINAP ligands has been synthesized and applied to the Ru‐catalyzed asymmetric hydrogenation of simple aryl ketones and 2‐arylacrylic acids. These dendronized poly(Ru‐BINAP) catalysts exhibited high catalytic activity and enantioselectivity, very similar to those obtained with the corresponding parent Ru(BINAP) and the Ru(BINAP)‐cored dendrimers. It was found that the pendant dendrons had a major impact on the solubility and the catalytic properties of the polymeric ligands. These polymeric catalysts could be easily recovered from the reaction solution by using solvent precipitation, and the reused catalyst showed no loss of activity or enantioselectivity.     

Polyethylene Glycol as an Environmentally Friendly and Recyclable Reaction Medium for Enantioselective Hydrogenation

Polyethylene glycol (PEG) was found to be an inexpensive, non‐toxic and recyclable reaction medium for ruthenium‐ and rhodium‐catalyzed asymmetric hydrogenation of 2‐arylacrylic acids (Ru‐catalyzed CC bond reduction), enamides (Rh‐catalyzed CC bond reduction), β‐keto esters and simple aromatic ketones (Ru‐catalyzed CO bond reduction). In all cases, high catalytic activities and enantioselectivities have been achieved, which are comparable to those obtained in conventional organic solvent systems. The Ru and Rh catalysts prepared with commercially available chiral diphosphine ligands could be readily recycled by simple extraction, as in the case of ionic liquids, and reused up to nine times without obvious loss of catalytic activity and enantioselectivity. The reduced products were obtained from the extracts in high isolated yields. These results indicate that PEGs as new reaction media are attractive alternatives to room temperature ionic liquids.     

手性膦配体在不对称催化氢化中的研究进展

综述了手性膦配体与Rh或Ru的配合物在活性羰基化合物手性催化氢化应用中的研究进展。     

Heterogeneous Asymmetric Hydrogenation of N-Heterocyclic Compounds: Hydrogenation of Tetrahydroisoquinoline Derivatives

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.     

手性树枝状大分子催化剂的合成及其在不对称催化中的应用进展

根据手性催化剂活性位点在树枝状大分子（Dendrimer）中位置的不同,综述了催化活性位点分别位于Dendrimer核心和外围以及聚合物固载化的手性Dendrimer催化剂的合成及其在不对称氢化、不对称氢转移、不对称Michael加成、硼烷对酮的不对称还原、不对称醇醛缩合反应、不对称Diels-Alder反应等不对称催化反应中的应用,重点论述了树枝状结构及代数对手性催化剂的活性、对映选择性及循环利用的影响,并对开发活性、选择性和稳定性更高的可回收手性Dendrimer催化剂前景进行展望。     

New Chiral Diphosphine Ligands Designed to have a Narrow Dihedral Angle in the Biaryl Backbone

A series of novel optically active diphosphine ligands, (4,4′‐bi‐1,3‐benzodioxole)‐5,5′‐diylbis(diarylphosphine)s ( 6 ), which are called SEGPHOS, has been designed and synthesized with dihedral angles in the Ru complexes being less than that in the corresponding BINAP‐Ru complex. The stereorecognition abilities of SEGPHOS‐Ru complex catalysts in the asymmetric catalytic hydrogenation of a wide variety of carbonyl compounds are superior to those observed with BINAP‐Ru complex catalysts.     

Chiral Bis(N‐sulfonylamino)phosphine‐ and TADDOL‐Phosphite‐Oxazoline Ligands: Synthesis and Application in Asymmetric Catalysis

A series of N,P‐ligands has been prepared, containing a chiral oxazoline ring and as a second chiral unit a bis(N‐sulfonylamino)phosphine group embedded in a diazaphospholidine ring or a cyclic phosphite group derived from TADDOL. These modular ligands are readily synthesized from chiral amino alcohols and chiral 1,2‐diamines or TADDOLs. Palladium and iridium complexes derived from these ligands were found to be efficient catalysts for enantioselective allylic alkylation and olefin hydrogenation, respectively.     

Preparation of recoverable Ru catalysts for liquid-phase oxidation and hydrogenation reactions

We here report the synthesis, characterization and catalytic performance of new supported Ru(III) and Ru(0) catalysts. In contrast to most supported catalysts, these new developed catalysts for oxidation and hydrogenation reactions were prepared using nearly the same synthetic strategy, and are easily recovered by magnetic separation from liquid phase reactions. The catalysts were found to be active in both forms, Ru(III) and Ru(0), for selective oxidation of alcohols and hydrogenation of olefins, respectively. The catalysts operate under mild conditions to activate molecular oxygen or molecular hydrogen to perform clean conversion of selected substrates. Aryl and alkyl alcohols were converted to aldehydes under mild conditions, with negligible metal leaching. If the metal is properly reduced, Ru(0) nanoparticles immobilized on the magnetic support surface are obtained, and the catalyst becomes active for hydrogenation reactions.     

Ruthenium catalyzed asymmetric transfer hydrogenation based on chiral P,N,O Schiff base ligands and crystal structure of a ruthenium(II) complex bearing chiral P,N,O Schiff base ligands

A ruthenium catalyst, generated in situ by heating the chiral P,N,O Schiff base ligand L (L = (S)-Ph₂PC₆H₄CNCHPhCH₂OH) with Ru(DMSO)₄Cl₂ in 2-propanol, is active for asymmetric transfer hydrogenation with best enantioselectivity up to 81%. A ruthenium complex of formula RuL₂Cl₂ is prepared and its crystal structure revealed that the two chiral P,N,O Schiff ligands are in meridional configuration. This complex is also an active catalyst for asymmetric transfer hydrogenation. However, the ‘[Ru(DMSO)₄]Cl₂ + chiral P,N,O ligand’ protocol displays better enantioselectivity.     

Study on liquid‐phase hydrogenation of paranitrotoluene over Ru‐based catalysts

This paper presented a study on the role of yttrium addition to Ru‐based catalysts for liquid phase paranitrotoluene hydrogenation reaction. An impregnation‐precipitation method was used for preparation of a series of yttrium doped Ru/NaY catalysts with yttrium content in the range of 0.0026–0.0052 g/g. Properties of the obtained samples were characterized and analyzed by X‐ray diffraction (XRD), H₂‐TPR, Transmission electron microscopy (TEM), ICP atomic emission spectroscopy, and Nitrogen adsorption‐desorption. The results revealed that catalytic activity of NaY supported Ru catalysts increased with the yttrium content at first, then decreased with the further increase of yttrium content. When yttrium content was 0.0033 g/g, a Ru‐Y/NaY² catalyst showed the most excellent performance of paranitrotoluene hydrogenation reaction (paranitrotoluene conversion and the selectivity toward P‐methyl‐cyclohexylamine reached 99.9 % and 82.5 %, respectively). In addition, to compare with the performance of Ru‐Y/NaY catalysts, the active carbon supported Ru catalysts were prepared using the same method in view of its higher surface area and adsorption capacity. Finally, the effect of solvent on the reaction over Ru‐Y/NaY² catalyst has been investigated, it was found that the best performance of paranitrotoluene hydrogenation reaction took place in protic solvents (isopropanol and ethanol). This was mainly ascribed to their polarity and hydrogen‐bond accepting capability.

     

Self-supported chiral catalysts for heterogeneous asymmetric catalysis

A conceptually new strategy for chiral catalyst immobilization, self-supported catalysts, in heterogeneous asymmetric catalysis is highlighted in the present article. Various homochiral metal-organic polymers with diverse structures have been designed and readily prepared through coordination assembly of modular polytypic/polyfunctional ligands and metal ions without using any supports. These polymers have been successfully employed as chiral catalysts in a variety of heterogeneous asymmetric ractions, including hydrogenation, epoxidation, sulfoxidation, carbonyl-ene reactions, diethylzinc addition, and Michael addition. The self-supported heterogeneous chiral catalysts showed activity and enanioselectivity comparable or even superior to those obtained with their corresponding homogeneous counterparts, and could be readily recovered and reused several times without significant loss of activity or enantioslectivity.     

手性铝化合物催化不对称氢转移反应的研究

以手性铝化合物为催化剂，异丙醇为氢源，进行芳香酮的不对称氢转移反应。在考察的酮类底物中，大部分具有较高收率，产物光学收率ee最高为83%。当配体和催化剂物质的量比为1时，反应效果最好。又考察一些手性二醇配体，其中，茚衍生的配体有着较好的手性诱导性能。     

Asymmetric transfer hydrogenation of ketones catalyzed by thermoregulated ionic liquid-regulating ruthenium complexes

A sulfonated chiral diamine ligand anion-based functionalized ionic liquid has been synthesized. Then the new ionic liquid-regulating ruthenium complexes were prepared successfully and employed as efficient catalysts for the asymmetric transfer hydrogenation of various ketones. The catalysts were highly efficient for the hydrogenation of a wide range of substrates bearing different functional groups and could be separated easily from the reaction mixture by thermoregulated phase separation, which can be efficiently recycled five times without significant changes in catalytic activity and enantioselectivity.     

Magnetically Recoverable Nanoparticles: Highly Efficient Catalysts for Asymmetric Transfer Hydrogenation of Aromatic Ketones in Aqueous Medium

Two magnetic chiral iridium and rhodium catalysts were prepared via directly postgrafting 1,2‐diphenylethylenediamine‐derived organic silica or 1,2‐cyclohexanediamine‐derived organic silica onto the silica‐coated iron oxide nanoparticles followed by complexation with iridium(III) or rhodium(III) complexes. During the asymmetric transfer hydrogenation of aromatic ketones in aqueous medium, the magnetic chiral catalysts exhibited high catalytic activities (up to 99% conversion) and enantioselectivities (up to 92% ee). Both catalysts could be recovered easily by magnetic separation and be reused ten times without significantly affecting their catalytic activities and enantioselectivities.     

用催化剂表面修饰以进行苯选择加氢制环己烯的研究

1 前言常规的气相苯催化加氢反应,苯环大π键一经打开就全部加氢到底,产物中只能获得环己烷而极难得到选择加氢产物环己烯。生成环己烷的反应从热力学上看远比生成环己烯的反应容易进行很多,并且环己烯也非常容易进一步加氢生成环己烷。但催化剂的表面经修饰剂作用后可根本改变其性能,从而改进催化活性及选择性,或实现常规方法不可能实现的反应,获得不易得到的产物。在经表面修饰的催化剂上进行苯加氢反应可获得选择加氢产物环     

Preparation of Ru metal nanoparticles in mesoporous materials: influence of sulfur on the hydrogenating activity

Hydrogenating catalysts were prepared by inserting Ru into the pores of mesoporous Al-MCM-41 materials by selective adsorption of [Ru(NH₃)₆]³⁺. Ru/support catalysts were obtained after reduction with H₂. The activities of these catalysts in hydrogenation reactions were compared to those of Ru/HY and Ru/SiO₂. The catalytic properties in the absence of sulfur were tested in benzene hydrogenation, and the intrinsic activities of all the catalysts (either supported on mesoporous materials or on zeolites) were identical. It was concluded from this result that the dispersion of the Ru metallic phase was similar for all these catalysts. These samples were tested in the tetralin hydrogenation in pure H₂ and in the presence of H₂S (330 ppm of H₂S in H₂). They were found to be much less active than the zeolite-supported catalysts in the presence of H₂S. It is proposed that the lower activity of the catalysts supported on mesoporous materials is either due to their milder acidity, as evidenced by NH₃-TPD, cumene cracking and pyridine desorption experiments, or to the localization of the Ru nanoparticles on alumina islands.     

Enantioselective Hydrogenation of β‐Acylamino Acrylates Catalyzed by Rhodium(I)‐Monophosphite Complexes

Chiral rhodium(I) complexes bearing monophosphite ligands, prepared from chiral Binol and (L )‐menthol, were found to be efficient catalysts for the asymmetric hydrogenation of β‐acylamino acrylates with ee values up to 94%.     

Hydrogenation of succinic acid to γ-butyrolactone (GBL) over ruthenium catalyst supported on surfactant-templated mesoporous carbon

Mesoporous carbon support (denoted as STC) was prepared by a surfactant-templating method for use as a support for ruthenium catalyst. For comparison, porous carbon (denoted as TC), spherical carbon (denoted as SC), and microporous carbon (denoted as DC) supports were also prepared by a templating method, hydrothermal method, and direct carbonization method, respectively. Ruthenium catalysts supported on carbon supports (Ru/C) were then prepared by an incipient wetness impregnation method. The Ru/C (Ru/DC, Ru/SC, Ru/TC, and Ru/STC) catalysts were characterized by FE-SEM, N₂ adsorption–desorption isotherm, BET, XRD, and HR-TEM analyses. Liquid-phase hydrogenation of succinic acid to γ-butyrolactone (GBL) was carried out over Ru/C catalysts in a batch reactor. In the hydrogenation of succinic acid, Ru/STC catalyst showed the highest conversion of succinic acid and the highest yield for GBL. The superior catalytic performance of Ru/STC catalyst compared to the other catalysts (Ru/TC, Ru/SC, and Ru/DC) was due to fine dispersion of ruthenium (ruthenium surface area). Thus, ruthenium surface area played a key role in determining the catalytic performance in the liquid-phase hydrogenation of succinic acid to GBL over Ru/C catalysts.     

Activation of carbon dioxide on Fe-catalysts

Development and evaluation of novel catalysts capable of activating CO₂ especially in CO₂ hydrogenation have been investigated. Several catalysts have been prepared, and characterized by CO₂ TPD. Their performance has been evaluated at 300 °C and 10 bar. All catalysts were active in CO₂ hydrogenation reaction with conversions of approximately 15–30% at 24 h time on stream. Potassium was found to enhance chain growth and to decrease the formation of methane. Ru promoter did not provide any benefit in activity or selectivity. Zr-promoted catalyst materials exhibited enhanced CO₂ adsorption and improved hydrocarbon yields.