Multinuclear Pd/Zn complex-catalyzed asymmetric alkylative ring-opening reaction of oxabicyclic alkenes

A multinuclear palladium catalyst can be used to realize the efficient catalytic asymmetric alkylative ring-opening reaction of oxabicyclic alkenes using dimethylzinc. The use of (R)-BINOL-PHOS bearing bisphosphine and diol moieties is essential for achieving excellent catalytic performance; the corresponding monophosphine and hydroxy-protected derivatives showed lower catalytic activities and/or enantioselectivities. The generation of Pd/Zn-multinuclear complexes is a key feature of the present catalysis.     

Effects of lanthanum on the properties of bifunctional Ni/HY catalyst

A series of lanthanum modified-Ni/HY bifunctional catalysts for n-octane hydroconversion were prepared by ion-exchange method, and the influence of lanthanum contents on the activity and the selectivity was investigated. Py-FTIR and CO-DRIFTS results indicated that the addition of lanthanum could adjust the acidity and the metal state over Ni/HY catalyst, and consequently change the ratio of metal to acid functions. It was found that the best catalytic performance at the lanthanum exchange of ca. 8 wt.% was due to the suitable metal/acid ratio.     

Synergism between molybdenum and lanthanum in the disproportionation of hydrogen peroxide into singlet oxygen

The catalytic disproportionation of hydrogen peroxide into singlet molecular oxygen was studied using the combined action of lanthanum(III) and molybdenum(VI). A synergistic effect was observed between both metals, resulting in a strong acceleration of the H2O2 disproportionation. An optimum in the catalytic activity was found at La/Mo and La/NaOH molar ratios of 4/1 and 1/3, respectively.     

Construction and Activity of a New Catalytic System in the Hydrolysis of Bis(4‐nitrophenyl) Phosphate Ester

A new catalytic system containing an unsaturated heterocyclic nitrogen ligand and lanthanum(III) was constructed and used as a catalyst in the hydrolysis of bis(4‐nitrophenyl) phosphate ester (BNPP) in this work. The results indicated that this catalytic system showed greater catalytic activity in the hydrolysis of BNPP and better reproducibility and stability than other similar lanthanum(III) systems. The catalytic rate of the BNPP hydrolysis was about 10⁷‐fold faster than that of its spontaneous hydrolysis at the same conditions. Compared with the previous Cu(II) or Ni(II) complex containing the same ligand in the water, the activity of the macrocyclic La(III) complex increases ca. 10³‐fold for BNPP catalytic hydrolysis. The experimental data showed that the monohydroxy complex made of the heterocyclic nitrogen ligand and lanthanum(III) is the real active species as a catalyst in BNPP catalytic hydrolysis.     

Reduction of organic halides with lanthanum metal: a novel generation method of alkyl radicals

Results of the reaction of alkyl halides with lanthanum metal have been shown. The reduction of alkyl iodide with 1/3 equiv of lanthanum metal efficiently proceeded to give the corresponding reductive dimerized products along with the formation of reduction and dehydroiodination products. In the case of alkyl bromides and chlorides, the reaction did not proceed under the same reaction conditions as that of alkyl iodides; however, the reaction was dramatically promoted by the addition of a catalytic amount of iodine. A reaction pathway including alkyl radicals was suggested.     

Atom-economy Synthesis of N-Substituted Carbamate from Urea Derivative and Dimethyl Carbonate Catalyzed by La/SiO_2: Characterization and Activity

A series of silica gel immobilized lanthanum catalysts were prepared for the atom‐economy synthesis of N‐substituted carbamates from urea derivatives and dimethyl carbonate. The La/SiO₂ catalysts with lanthanum loadings varied from 1.3 wt% to 8.5 wt% were characterized by AES, BET, XRD, TEM, FT‐IR, XPS and TPD. According to the characterization, lanthanum species with particle sizes of 5–10 nm on the surface of silica gel were formed. The catalysts were all amorphous and the surface areas were 336.5–530.2 m²/g. NH₃‐TPD analysis showed that all samples exhibited similar acid strength with different acid amounts. FT‐IR measurement indicated that the component of lanthanum species on the catalyst surface were La(OH)₃, LaOOH and hydrated La₂O₃. Also, the peak value of the absolute amount of LaOOH was obtained with 4.3 wt% lanthanum loading. The BET surface area decreased dramatically when the lanthanum loading was above 4.3 wt%. In consideration of the results obtained from the catalytic reactions, it could be concluded that LaOOH was the possible active species and high surface area was important for the high catalytic activity.     

稀土水滑石的合成与表征（Ⅰ）

合成了稀土镧在层晶格骨架中的水滑石,经粉末X射线衍射、红外光谱、X射线光电子能谱及离子交换法进行了表征.通过催化苯酐与正己醇的酯化反应,表明样品具有催化活性.     

Direct, catalytic enantioselective nitroaldol (Henry) reaction of trifluoromethyl ketones: an asymmetric entry to alpha-trifluoromethyl-substituted quaternary carbons

Herein we describe the first direct, catalytic enantioselective nitroaldol (Henry) reaction of simple alpha-trifluoromethyl ketones with nitromethane using a chiral monometallic lanthanum(III) triflate salt complex, namely [(Delta,S,S,S)-Binolam]3.La(OTf)3, as enantioselective catalyst. The resulting alpha-trifluoromethyl tertiary nitroaldols were obtained in moderate to high yields (up to 93%) and enantioselectivities (up to 98% ee). These adducts are versatile chiral building blocks and may be reduced (NiCl2/NaBH4) to their beta-amino-alpha-trifluoromethyl tertiary alcohols without loss of enantiomeric purity.     

La2O3对Pd/Al2O3催化蒽醌氢化制H2O2性能的影响

 采用湿浸法制备了用于蒽醌氢化制H2O2的La2O3促进的Pd/Al2O3催化剂,并考察了不同La2O3含量对催化性能的影响. 采用XRD,N2物理吸附,CO2-TPD,H2-O2滴定和电子探针等技术对催化剂进行了表征. 结果表明,加入适量的La2O3能够抑制高温焙烧时Al2O3晶粒的长大,增大催化剂的比表面积,提高金属Pd的分散度,增强载体表面碱性,提高催化剂表面的Pd浓度,减小Pd层厚度,从而提高催化剂的氢化活性. 加入La2O3可使催化剂的Pd负载量由0.281%降至0.188%,而催化剂活性提高了44%.     

Fritsch-Buttenberg-Wiechell rearrangement to alkynes from gem-dihaloalkenes with lanthanum metal

The first example of the FBW rearrangement using of lanthanum metal and a catalytic amount of iodine was disclosed. When gem-diiodo- and gem-dibromoalkenes were treated with lanthanum metal in the presence of a catalytic amount of iodine, the reductive dehalogenation of these compounds smoothly proceeded to produce the corresponding alkynes in moderate to good yields.     

The studies of hydrodesulfurization activity over molybdenum catalysts supported on Al-MCM-41 modified by lanthanum

A series of lanthanum modified Al-MCM-41 substrates served as supports to prepare the Mo/La-Al-MCM-41 catalysts. The catalysts were characterized by XRD, BET, FT-IR, XPS, TPR and TPD, and their catalytic activities were determined for thiophene hydrodesulfurization (HDS).     

Regulation of the rate of hydrolysis of phosphorus acid esters in organized systems based on amphiphilic pyrimidinophanes

The aggregation and catalytic activity of supramolecular systems based on new macrocyclic dimeric surfactants (pyrimidinophanes) was studied both in the absence and in the presence of polyethyleneimine (PEI). It was found that the critical micelle concentrations measured by tensiometry were independent of the structure of surfactants. The morphology of aggregates was responsible for various characters of the catalytic effects of pyrimidinophanes in the hydrolysis of phosphonic acid esters. A less hydrophobic pyrimidinophane exhibited a typical effect of cationic surfactants to accelerate the reaction both in the absence and in the presence of PEI. Unlike cationic micelles, a heminal-type pyrimidinophane exhibited an anomalous behavior: it had no effect on the rates of hydrolysis of the substrates and did not inhibit the hydrolysis. Upon the addition of lanthanum ions, the catalytic activity of dimeric surfactants increased. The overall catalytic effect due to the action of supramolecular systems based on pyrimidinophanes, PEI, and lanthanum ions can increase the rates of hydrolysis of the substrates by three orders of magnitude, as compared with that of alkaline hydrolysis.     

Palladium-catalyzed asymmetric hydrogenation of functionalized ketones

[reaction: see text]. A novel catalytic system for asymmetric hydrogenation of functionalized ketones has been developed using a Pd/bisphosphine complex as the catalyst in 2,2,2-trifluoroethanol. The reaction exhibits high enantioselectivity, and up to 92.2% ee was obtained.     

N-Boc-L-valine-connected amidomonophosphane rhodium(I) catalyst for asymmetric arylation of N-tosylarylimines with arylboroxines

A catalytic asymmetric arylation of sterically tuned imines with arylboroxines was developed by using N-Boc-l-valine-connected amidomonophosphane rhodium(I) catalyst in n-PrOH. The TMS group used for the steric tuning of imines is convertible to other functionalities that are applicable as a key foothold for the carbon-carbon bond-forming coupling reactions.     

Catalytic asymmetric synthesis of (S)-oxybutynin and a versatile intermediate for antimuscarinic agents

A practical synthesis of (S)-oxybutynin, a muscarinic receptor antagonist, using catalytic enantioselective cyanosilylation of cyclohexyl phenyl ketone (9a) as a key step is described. The key reaction proceeded with 94% ee using 1 mol% of Gd-1 catalyst, and was performed on a 100 g-scale. In addition, a short catalytic enantioselective synthesis of the versatile intermediate for Scios Nova analogues of antimuscarinic agents (7) is described. Application of the catalytic enantioselective cyanosilylation to ketones containing two sterically similar substituents on the carbonyl group is also discussed.     

CH4 reforming with CO2 for syngas production over La2O3 promoted Ni catalysts supported on mesoporous nanostructured γ-Al2O3

Nanostructured γ-Al₂O₃ with high surface area and mesoporous structure was synthesized by sol-gel method and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by XRD, N₂ adsorption-desorption, TPR, TPO, TPH, NH₃-TPD and SEM techniques. The BET analysis showed a high surface area of 204 m²·g⁻¹ and a narrow pore-size distribution centered at a diameter of 5.5 nm for catalyst support. The BET results revealed that addition of lanthanum oxide to aluminum oxide decreased the specific surface area. In addition, TPR results showed that addition of lanthanum oxide increased the reducibility of nickel catalyst. The catalytic evaluation results showed an increase in methane conversion with increasing lanthanum oxide to 3 mol% and further increase in lanthanum content decreased the catalytic activity. TPO analysis revealed that the coke deposition decreased with increasing lanthanum oxide to 3 mol%. SEM and TPH analyses confirmed the formation of whisker type carbon over the spent catalysts. Addition of steam and O₂ to dry reforming feed increased the methane conversion and led to carbon free operation in combined processes.     

A catalytic asymmetric Ugi-type reaction with acyclic azomethine imines

An unconventional Ugi: A catalytic asymmetric Ugi-type reaction can be realized by use of N'-alkylbenzohydrazide, instead of a conventional amine, in the presence of an axially chiral dicarboxylic acid. The reaction proceeds through a key acyclic azomethine imine intermediate, which has recently emerged as a promising electrophile in asymmetric catalysis.     

Catalytic asymmetric synthesis of a potent thiomarinol antibiotic

Thiomarinols, isolated from the bacterium Alteromonas rava sp. nov. SANK 73390, are potent marine antibiotics that possess both Gram-positive and Gram-negative activity. The first total synthesis of a member of the thiomarinol class of marine antibiotics was achieved in a remarkable global yield of 22% (from 3-boronoacrolein pinacolate). The highlight of this synthesis is the efficient catalytic enantio-, regio-, E/Z-, and diastereoselective three-component inverse electron demand Diels-Alder/allylboration sequence. This key operation provides a rare example of an enantioselective HDA reaction involving acyclic 2-substituted enol ethers, and it featured an unusual but fortuitous kinetic selection that favored the requisite Z-dienophile.     

Supramolecular catalytic systems based on 1, 4-diazabicyclo[2.2.2]octane,its alkylated quaternary derivatives,and lanthanum nitrate

Spectrophotometry was used to study the catalytic effects of the systems composed of N-monoand N, N-dialkylated 1, 4-diazabicyclo[2.2.2]octanes and lanthanum nitrate on the hydrolysis rate of O-alkyl O-4-nitrophenyl chloromethylphosphonates (Alk = Et, Buⁿ, and n-hexyl). The mechanism of action and efficiency of the catalytic system depend on the structure of the heterocycle, its propensity to aggregation and complexation with the lanthanum cation, and the relative content of the components in solution. The maximum catalytic effect (a ～115-fold increase in the hydrolysis rate constant) was achieved in micellar solutions of the cationic monoalkylated derivative of 1, 4-diazabicyclo[2.2.2]octane and lanthanum nitrate.

     

Rhodium-catalyzed asymmetric hydroarylation of diphenylphosphinylallenes with arylboronic acids

Rhodium-catalyzed asymmetric hydroarylation of diphenylphosphinylallenes with arylboronic acids proceeded in high yields with high regio- and enantioselectivity to give chiral allylphosphine oxides of up to 98% ee. The structural determination of the key intermediate, a pi-allylrhodium complex, was successful to establish the catalytic cycle of the reaction.