Catalysis of Ugi four component coupling reactions by rare earth metal triflates

Substoichiometric quantities of scandium and ytterbium triflate increase the yield of Ugi four component coupling reactions of aromatic aldehydes 2- to 7-fold. These rare earth metal triflates enhance the reaction yields primarily via activation of the imine intermediate of this multicomponent reaction.     

Surface-initiated group transfer polymerization mediated by rare earth metal catalysts

We present the first example of a surface-initiated group transfer polymerization (SI-GTP) mediated by rare earth metal catalysts for polymer brush synthesis. The experimentally facile method allows rapid grafting of polymer brushes with a thickness of >150 nm in <5 min at room temperature. We show the preparation of common poly(methacrylate) brushes and demonstrate that SI-GTP is a versatile route for the preparation of novel polymer brushes. The method gives access to both thermoresponsive and proton-conducting brush layers.     

Direct N-acetyl enamine formation: lithium bromide mediated addition of methyllithium to nitriles

An improved protocol for N-acetyl enamine formation is disclosed which involves LiBr-mediated addition of MeLi to substituted nitriles. The resulting enamides are isolated in high yields and excellent purity which permits subsequent hydrogenation at very low catalyst loading.     

Hydrogenation of carbon monoxide by tetranuclear rare earth metal polyhydrido complexes. Selective formation of ethylene and isolation of well-defined polyoxo rare earth metal clusters

The reaction of the tetranuclear rare earth metal polyhydrido complexes {Cp'Ln(mu-H)2}4(THF) (Cp' = C5Me4SiMe3, Ln = Y (1a), Lu (1b)) with carbon monoxide (1 atm) yielded ethylene and the corresponding tetraoxo cubane complexes (Cp'Ln)4(mu3-O)4 (Ln = Y (5a), Lu (5b)). Stepwise formation of some key reaction intermediates, such as oxymethylene complexes (Cp'Ln)4(mu-OCH2)(mu-H)6(THF) (Ln = Y (2a), Lu (2b)), enolate species (Cp'Y)4(OCH=CH2)(mu-O)(mu-H)5(THF) (3), and dioxo complex (Cp'Y)4(mu3-O)2(mu-H)4(THF) (4), was confirmed. The molecular structures of 2a, 4, and 5b were determined by X-ray diffraction studies.     

Extraction of rare earth metal samarium by microemulsion

The influence of the concentration of sodium oleate (NaOL), alcohol and the nature of the internal water phase on the water content of microemulsion was studied. The effect of the concentration of NaOL, sodium stearate, alcohol, salting-out agent, Alamine 336 added and of the contact time, volume ratio of the aqueous to microemulsion (R) and temperature on the extraction yield of samarium was investigated. The result shows that the extraction of samarium is effective under well-defined conditions utilizing WinsorII microemulsion systems.     

Rare earth metal triflates catalyzed electrophilic nitration using N2O5

A mild,efficient and eco-friendly process for the electrophilic nitration is described using N₂O₅ as a green nitrating agent in the presence of rare earth metal triflates[RE（OTf）₃]under mild conditions.     

Fusion temperatures of rare earth metal trihalides

The fusion temperatures (T _f) of rare earth metal trihalides LnX₃ (Ln=La–Lu, Y; X=Cl, Br, I) typically decrease to a minimum, before taking on an upward trend as the ionic radius of Ln³⁺ decreases. This trend is associated with the variations in the energetic stability of the coordination polyhedron around Ln³⁺. A good correlation is obtained between the variations in the energetic stability of the crystal structure of LnX₃ andT _f.

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Zusammenfassung Die Schmelztemperaturen (T _f) der Trihalide der Seltenen Erdmetalle LnX₃ (Ln=La-Lu, Y; X=Cl, Br, J) gehen mit abnehmendem Ionenradius von Ln³⁺ auf typische Weise durch ein Minimum. Dieser Trend wird mit den Unterschieden in der energetischen Stabilität der um das Ln³⁺-Ion angeordneten Koordinationspolyeder in Verbindung gebracht. Es wurde eine gute Korrelation zwischen der energetischen Stabilität der Kristallstruktur undT _f erhalten.

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LnX₃ (Ln=La-Lu,Y; =l,, I) . Ln³⁺. LnX₃ .

     

Vibration spectra of rare earth metal tantalates

Infrared and Raman spectra of TRTa₇O₁₉ (TR = La, Nd, Eu) have been considered. Their structures have not been determined yet. Vibration spectra enable to assume the presence of TaO₄-tetrahedrons in tantalates. Vibration spectra of TRTaO₄ have been considered as well. Vibration spectra of TR₃TaO₇ have been recorded. Crystals of Le₃TaO₇, Nd₃TaO₇ are isostructural to veberite, while those of Eu₃TaO₇ to pyrochlorine. Factor-group analysis of the vibrations of the above samples of rare earth metal tantalates has been performed.     

Complex formation of p-nitrocalix[6]arene with rare earth metal ions.

p-Nitrocalix[6]arene (CALX-N6, L) formed a 1:1 metal complex, ML, with light rare earth metal ions (M3+), such as La3+, Pr3+ and Nd3+ except Ce3+, but formed a 1:2 (M(3+):L) complex, ML2 (the charge of the complex is omitted) with heavy rare earth metal ions, such as Sm(3+)-Lu3+ including Y3+. The conditional stability constants of these 1:1 and 1:2 complexes, KML and KML2, were measured by a ligand displacement method using absorption spectrophotometry in 4% (v/v) acetone aqueous solution at pH 9.65 +/- 0.15 and 25 degrees C.     

Generation of rare earth metal clusters by means of the gas-aggregation technique

Generation of rare-earth clusters is achieved using a gas aggregation technique. Varying the nucleation conditions induces a change in the relative cluster abundances. This can be understood in terms of competing cubic versus icosahedron structures.     

Developments of rare earth metal catalysts for olefin polymerization

This review article describes recent developments in rare earth metal complexes as polymerization catalysts, focusing on the polymerization of ethylene and α-olefins. Most of this kind of catalysts had been based on metallocene type complexes, and their catalytic behaviors are surveyed. Advanced series of half-metallocene and non-Cp type catalyst systems are also summarized.     

Phase diagrams for systems formed by manganese and rare earth metal oxides

We analyze the advantages and disadvantages of various methods for representing P-T-x diagrams of three-component systems and their fragments in various coordinates.     

Catalytic addition of terminal alkynes to carbodiimides by half-sandwich rare earth metal complexes

The catalytic addition of terminal alkynes to carbodiimides has been achieved for the first time by use of half-sandwich rare earth metal complexes, such as {Me2Si(C5Me4)(NPh)}Y(CH2SiMe3)(THF)2, which offers a straightforward, atom-economic route to the N,N'-disubstituted propiolamidines which contain a conjugated C-C triple bond, a new family of amidines which were difficult to prepare by other means. A rare earth metal amidinate species was confirmed to be a true catalytic species in this process, thus demonstrating for the first time that an amidinate unit, though being often used as an ancillary ligand for various organometallic complexes, can itself participate in a catalytic reaction under appropriate conditions.     

Catalytic enantioselective construction of tetrasubstituted carbons by self-assembled poly rare earth metal complexes

Rare earth metal-based enantioselective catalysts that can promote practical cyanation reactions of ketones and ketoimines were developed. These catalytic enantioselective tetrasubstituted carbon-forming reactions are useful platforms for the synthesis of biologically active compounds. ESI-MS and crystallographic studies of the asymmetric catalysts revealed that the active catalysts are polymetallic complexes produced through the assembly of modules. The higher-order structure of the polymetallic complexes has strong effects on catalyst activity and enantioselectivity. Controlling the higher-order structure of artificial polymetallic asymmetric catalysts is a new strategy for optimizing asymmetric catalysts. Recent progress in this approach is also described.     

辉光放电质谱法测定稀土矿中的15种稀土元素

利用高纯铜粉与稀土矿石粉末均匀混合压片制样.混合15种高纯稀土氧化物制样建立标准工作曲线,校正15种稀土元素相对灵敏度因子,再进行定量分析.结果 表明,稀土元素工作曲线的线性方程相关系数R2均大于0.996,相对标准偏差(RSD)小于5％,满足定量分析要求.测定结果与电感耦合等离子体质谱法(ICP-MS)和电感耦合等离...     

A study of the degradation of ester-modified epoxy resins obtained by cationic copolymerization of DGEBA with γ-lactones initiated by rare earth triflates

The thermal degradation of new thermosetting materials prepared by cationic copolymerization of mixtures with different proportions of diglycidylether of bisphenol A (DGEBA) with γ-valerolactone (γ-VL) or α-methyl-γ-butyrolactone (γ-MBL) initiated by scandium, ytterbium or lanthanum triflate and a complex of boron trifluoride was investigated. To study the thermal degradation thermogravimetry (TGA) was used. The materials are more degradable than conventional epoxy resins due to the presence of ester groups in the polymer chain, which are broken at the beginning of degradation. The degradability increased with the proportion of linear ester groups and the Lewis acidity of the initiator used in the polymerization and when the proportion of lactone in the initial mixture increased. The kinetic parameters of the degradation were calculated from TGA data by applying isoconversional procedures.     

Thermal decomposition of some rare earth metal cupferrates and neocupferrates

The thermal decomposition of the eupferrates and neocupferrates of europium, terbium, dysprosium, holmium, erbium, and ytterbium was studied on the thermobalance. The metal chelates possessed poor thermal stability as well as a pronounced tendency to Coprecipitate reagent. The minimum oxide level temperatures for the metal cupferrates were : Eu, 570°; Tb, 540°; Dy, 550°; Ho, 610°; Er, 550° and Yb, 520°. The minimum oxide level temperatures for the metal neocupferrates were: Eu, 560°; Tb 565°; Dy, 540°; Ho,445°; Er, 530°; and Yb, 485°.