Rare Earth Metal Triflates Research Articles

ChemInform Abstract: Direct Formation of β‐Glycosides of N‐Acetyl Glycosamines Mediated by Rare Earth Metal Triflates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

希土類およびハフニウムトリフラートを用いたカルボカチオン生成と各種求核試薬との反応

The rare earth metal and hafnium triflate-catalyzed cationic benzylation of various nucleophiles using benzylic alcohols is described. The reaction of benzylic alcohols with aromatic compounds in nitromethane in the presence of catalytic amount of metal triflate gave Friedel-Crafts-type benzylation products in high yield. Direct use of the alcohol as a source of an electrophile produces only water as a side product. Water-tolerant rare-earth metal triflates effectively catalyzed the alkylation under non-anhydrous conditions and the catalysts could be reused up to three times. The benzylation system also showed compatibility over a wide range of nucleophiles such as olefin, allylsilane, enol acetates, diketones, ketoesters, alcohols, and amides. The reaction conditions of various combinations of benzylic alcohols and nucleophiles were easily optimized by the two-dimensional catalysts-temperature screenings using La, Yb, Sc, and Hf triflates.

Characterization of new reworkable thermosetting coatings obtained by cationic and anionic curing of DGEBA and some Meldrum acid derivatives

Rare earth metal triflates, BF3·MEA and N,N-dimethylaminopyridine (DMAP) were used as cationic and anionic initiators to cure mixtures of diglycidylether of bisphenol A (DGEBA) and Meldrum acid (2,2-dimethyl-4,6-dioxo-1,3-dioxane) derivatives in several proportions. The copolymerization process led to poly(ether-ester) three-dimensional networks. The linear ester groups in the final materials were evaluated by Fourier transform infrared in the attenuated-total-reflection mode (FTIR/ATR).The shrinkage after curing and the thermal degradability of the materials on varying the lactone structure, comonomer ratio and the initiator used were evaluated and related to the chemical structure of the final network. The addition of lactones to the reactive mixture reduced the shrinkage on curing, which improve the reliability of coatings. The materials obtained were more degradable than conventional epoxy resins due to the tertiary alkyl ester groups incorporated into the network, which facilitates to remove the coatings when the service life is over.The flexibilizing effect of the linear ester introduced into the network by copolymerization with DGEBA was studied by DMTA. Microhardness and adhesion characteristics of these materials, which are interesting characteristics in coating industries, were also evaluated.

Study on the effect of rare earth metal triflates as initiators in the cationic curing of DGEBA/γ-valerolactone mixtures and characterization of the thermosets obtained

Abstract The thermal cationic curing of mixtures in different proportions of diglycidylether of bisphenol A (DGEBA) with γ-valerolactone (γ-VL) initiated by scandium, ytterbium and lanthanum triflates or a conventional BF3·MEA initiator was investigated. The non-isothermal differential scanning calorimetry (DSC) experiments at a controlled heating rate were used to evaluate the evolution of the reactive systems. BF3·MEA and rare earth metal triflates initiated curing systems follow a different evolution. Among rare earth metal triflates tested, the scandium was the most active initiator. The phenomenological changes that take place during curing were studied and represented in a time-temperature-transformation (TTT) diagram. Some characteristics of the materials were also evaluated.

ChemInform Abstract: Catalysis of Ugi Four‐Component Coupling Reactions by Rare Earth Metal Triflates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

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.

Direct formation of β-glycosides of N-acetyl glycosamines mediated by rare earth metal triflates

A direct, mild and efficient protocol for the preparation of beta-glycosides of N-acetyl glucosamine (GlcNAc) and N-acetyl galactosamine (GalNAc) has been developed using peracetylated beta-GlcNAc and beta-GalNAc as donors. All rare Earth metal triflate promoters screened were found to promote glycosylation with Sc(OTf)(3) being superior in terms of reaction rate. Simple alcohol glycosylation was found to proceed smoothly in refluxing dichloromethane, whereas higher temperatures under microwave conditions were needed to attain acceptable yields with less reactive, carbohydrate based glycosyl acceptors. The protocol developed was applied to provide the first example of direct chemical formation of a disaccharide using both GlcNAc as a glycosyl donor and acceptor. The alpha-acetate donor was found to be significantly less reactive than the corresponding beta-anomer necessitating higher reaction temperatures under which glycoside anomerisation was found to occur. It was established, that the anomerisation only took place in the presence of both Sc(OTf)(3) and acetic acid.

Rare earth metal triflates promoted Diels–Alder reactions in ionic liquids

Abstract Rare earth metal triflates, when used with ionic liquids can promote Diels–Alder reactions carried out with different dienes and dienophiles suggesting an enhancement in the catalytic power of the triflates in ionic liquids. It is possible to recover and reuse the ionic liquid phase with triflates to give comparable yields and stereoselectivities even after six cycles.

Ring-opening polymerization of lactones by rare-earth metal triflates and by their reusable system in ionic liquids

The ring-opening polymerizations (ROPs) of lactones catalyzed by rare-earth metal trifluoromethanesulfonates (triflates) (RE(OTf) 3) were examined. Among various complexes, scandium triflate (Sc(OTf) 3) emerged as an effective catalyst in toluene. The ROP of lactones by Sc(OTf) 3 proceeded in a living fashion, and the number of polymer molecules was controlled by the amount of protic additives such as benzyl alcohol and H 2O. In other words, one molecule of Sc(OTf) 3 catalytically produced a number of polymer molecules (up to 40 molecules) depending on the amount of protic additives. The plausible mechanism was depicted as an activated monomer mechanism. The polylactones with a number-average molecular weight over 25,000 were successfully synthesized. Immobilization of RE(OTf) 3 was investigated in three ionic liquids, and cerium triflate (Ce(OTf) 4) showed relatively high catalytic activity in a biphasic system of 1-butyl-3-methylimidazolium hexafluoroantimonate and toluene in the ROP of ɛ-caprolactone (CL). The ionic liquid containing Ce(OTf) 4 was used, at least three times, in the ROP of CL without losing catalytic activity.

Rare-earth metal triflates catalyzed three-component coupling of aldehydes, ketones or ketoesters and benzyl carbamate: An efficient one-pot stereoselective synthesis of Cbz-protected β-amino carbonyl compounds

Sc(OTf) 3 and Yb(OTf) 3 have been found to be efficient catalysts for one-pot three-component coupling of aldehydes, ketones or ketoesters and benzyl carbamate in acetonitrile at room temperature to furnish the corresponding Cbz-protected β-amino ketones in impressive yields and good diastereoselectivity.

Rare earth triflate catalysts in the synthesis of Vitamin E and its derivatives

Vitamin E is known as the most important fat-soluble antioxidant in biological systems. The scale for commercially produced (all- rac)-α-tocopherol reaches over 25,000 tonnes per year. The known processes for the synthesis of α-tocopherol suffer from disadvantages like formation of by-products and waste-water problem. To overcome these drawbacks, new types of catalysts have been developed. These are rare earth metal triflates, e.g. Bi(OTf) 3, Ga(OTf) 3, Tm(OTf) 3 or Hf(OTf) 4. This new approach to Vitamin E or derivatives thereof has several advantages, based on high yields (above 94%) and selectivities.

Creation of monomeric La complexes on apatite surfaces and their application as heterogeneous catalysts for Michael reactions

Using a cation-exchange method, an equimolar substitution of La3+ for Ca2+ occurred by the treatment of stoichiometric hydroxyapatite (HAP: Ca10(PO4)6(OH)2) with an aqueous solution of La(OTf)3, affording a monomeric hydroxyapatite-bound La complex (LaHAP). Physicochemical characterization by means of XRD, XPS, IR, and La K-edge XAFS analyses proved that a monomeric La3+ phosphate complex was generated on its surface. Such monomeric La3+ species function as an efficient heterogeneous catalyst for the Michael reaction of 1,3-dicarbonyls with enones under aqueous or solvent-free conditions. The work-up procedure is straightforward and the spent catalyst could be recycled without any loss of the catalytic activity. Further application to an asymmetric version was also investigated using various apatite catalysts modified with chiral organic ligands. Enantioselectivity was found to depend on the chiral ligand, solvent, and rare earth metal triflate precursor (RE(OTf)3) for the reaction of methyl 1-oxoindan-2-carboxylate with methyl vinyl ketone. Under optimized reaction conditions, a monomeric fluoroapatite-bound La complex catalyst modified with (R,R)-tartaric acid (TA-LaFAP) provided the Michael adduct quantitatively in up to 60% ee.

Recent Advances in Rare Earth Metal Triflate Catalyzed Organic Synthesis in Green Media

AbstractFor Abstract see ChemInform Abstract in Full Text.

Friedel–Crafts alkylation of aromatics with benzyl alcohols catalyzed by rare earth metal triflates supported on MCM-41 mesoporous silica

Friedel–Crafts alkylation of aromatics with benzyl alcohol as alkylating agent has been investigated over rare earth metal triflates, Sc(OTf) 3, Hf(OTf) 4, La(OTf) 3, and Yb(OTf) 3 supported on MCM-41. The catalytic activity of triflates, particularly, Sc(OTf) 3 and Hf(OTf) 4 was enhanced by being loaded onto MCM-41 because of increased dispersion, and gave the benzylated product in high yield. They were reusable without the loss of the activity for their recycling. Water generated during the benzylation with benzyl alcohol (BnOH) did not affect on the catalytic activity of the Sc(OTf) 3 supported on MCM-41 (Sc(OTf) 3/MCM-41). The catalytic activity of Sc(OTf) 3/MCM-41 was not affected by the further addition of water equimolar to BnOH. The benzylation of aromatics (toluene, p-xylene, mesitylene, and naphthalene) with benzyl alcohol, and of benzene with benzyl alcohols (4-methylbenzyl alcohol and 4-chlorobenzyl alcohol) were studied over Sc(OTf) 3/MCM-41 at 353 K. The rate of the benzylation of benzene over Sc(OTf) 3/MCM-41 was accelerated by electron donating groups and retarded by electron withdrawing groups. The benzylation of aromatics proceeds with direct benzylation with benzyl alcohol, and the dehydration product, i.e., dibenzyl ether (DBE), which is a by-product formed during the benzylation of aromatics; however, it participates in the benzylation with benzene via BnOH with the decrease in BnOH.

Chiral 2,6‐Bis(oxazolinyl)pyridine—Rare Earth Metal Complexes as Catalysts for Highly Enantioselective 1,3‐Dipolar Cycloaddition Reactions of 2‐Benzopyrylium‐4‐olates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Recent Advances in Rare Earth-Metal Triflate Catalyzed Organic Synthesis in Green Media

Rare-earth metal triflates have been well established as potent environmentally-benign Lewis acids. This review summarizes the recent progress of RE(OTf)3 catalyzed organic synthesis in green media including water, ionic liquids, super critical CO2, solvent-free conditions as well as solid supported synthesis. Keywords: rare-earth metal triflates, aqueous phase, ionic liquids, super critical co2, solvent free, solid support, organic synthesis, green chemistry

Chiral 2,6-Bis(oxazolinyl)pyridine−Rare Earth Metal Complexes as Catalysts for Highly Enantioselective 1,3-Dipolar Cycloaddition Reactions of 2-Benzopyrylium-4-olates

Significant levels of enantioselectivity were obtained in 1,3-dipolar cycloadditions of 2-benzopyrylium-4-olate generated from the Rh(2)(OAc)(4)-catalyzed decomposition of o-methoxycarbonyl-alpha-diazoacetophenone. This reaction utilized chiral 2,6-bis(oxazolinyl)pyridine (Pybox)--rare earth metal triflate complexes as chiral Lewis acid catalysts. The reactions with several benzyloxyacetaldehyde derivatives catalyzed by a Sc(III)--Pybox-i-Pr complex (10 mol %) proceeded smoothly to yield endo-adducts selectively with high enantioselectivity (up to 93% ee). For the reaction with benzyl pyruvate, the Sc(III)-Pybox-i-Pr complex (10 mol %) catalyzed the reaction effectively in the presence of trifluoroacetic acid (10 mol %) to yield an exo-adduct with both high diastereo- and enantioselectivity (94% ee). This catalytic system was efficiently applied to the reactions with several other alpha-keto esters with high exo- and enantioselectivities (up to 95% ee). In contrast to the reaction with carbonyl compounds, Yb(III)--Pybox-Ph complex (10 mol %) was found to be effective to obtain high enantioselectivity (96% ee) of diastereoselectively produced exo-cycloadduct in the reaction with 3-acryloyl-2-oxazolidinone.

Novel Initiating System for the Stereocontrolled Radical Polymerization of Acrylamides: Alkyl Bromide/Rare Earth Metal Triflate System

A novel radical initiating system — rare-earth metal triflate [Y(OTf)3, Yb(OTf)3, Lu(OTf)3, Sc(OTf)3] and alkyl halide containing α-esters (ethyl 2-bromoisobutyrate and ethyl 2-bromopropionate) or α-amide (N,N-dimethyl-2-bromo-2-methylpropanamide) was used for the stereocontrolled radical polymerization of N-isopropylacrylamide (NIPAM). The Lewis acids serve a dual role as the promoter of the radical initiation and the controller of the stereospecific polymerization. The effects of the Lewis acid type and concentration, the initiator type and concentration, solvents, and temperature on the polymerization of NIPAM have been reported. The chain-end structure of the resulting polymer was determined by 1H NMR. We also extended this initiating system for the polymerization of N,N-dimethylacrylamide, styrene, n-butyl acrylate, and methyl methacrylate.

Rare-earth metal triflates as versatile catalysts for the chloromethylation of aromatic hydrocarbons

Rare-earth metal triflates, such as Sc(OTf)3, Yb(OTf)3, and Sm(OTf)3 work as highly effective catalysts for the chloromethylation of aromatic hydrocarbons with hydrochloric acid and trioxane. They are active enough in aqueous solution at a concentration of less than 1–5% of the substrate under heterogeneous conditions of organic and aqueous phases. The triflate stays in the aqueous phase after the catalysis, and the organic products are easily separated from the catalyst. Sc(OTf)3 was stable under the reaction conditions. The catalyst in the aqueous solution could be recycled and used for further reactions without significant loss of activity. The chloromethylation of m-xylene catalyzed by Sc(OTf)3 gave 2,5-bis(chloromethyl)-m-xylene with 1,2,4,5-substitution, which is expected to be a key intermediate for pyromellitic dianhydride. The catalysis occurred via the formation of a chloromethylated triflate complex, and electrophilic addition to an aromatic hydrocarbon.

Stereoselectivity in 1,3‐Dipolar Cycloaddition Reactions of 2‐Benzopyrylium‐4‐olate with Acrylic Acid Derivatives Catalyzed by Rare Earth Metal Triflates.

AbstractFor Abstract see ChemInform Abstract in Full Text.