Lanthanide Triflates Research Articles

Syntheses of aliphatic polyesters catalyzed by lanthanide triflates

AbstractPolycondensations of 1,6‐hexane diol and sebacic acid were conducted in bulk with addition of a lanthanide triflate as acidic catalyst. With exception of promethium triflate all lanthanide triflates were studied. A particularly low molecular weight was obtained with neodym triflate and the best results with samarium triflate. With Sm(OTf)3 weight average (Mw) values up to 65 kDa (uncorrected SEC data) were achieved after optimization of the reaction conditions. Comparison of these results with those obtained from bismuth, magnesium, and zinc triflates, on the one hand, and comparison with the acidities of all catalysts, on the other, indicates that the esterification mechanism involves complexation of monomer by metal ions. Preparation of multiblock copoly(ether ester)s failed due to insufficient incorporation of poly(tetrahydrofuran) diols. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 170–177, 2009

ChemInform Abstract: Regioselective Green Anomeric Deacetylation Catalyzed by Lanthanide 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.

Experimental and Theoretical Approaches Toward Anion‐Responsive Tripod–Lanthanide Complexes: Mixed‐Donor Ligand Effects on Lanthanide Complexation and Luminescence Sensing Profiles

A new series of tripods were designed to form anion-responsive, luminescent lanthanide complexes. These tripods contain pyridine, thiazole, pyrazine, or quinoline chromophores combined with amide carbonyl oxygen and tertiary nitrogen atoms. Crystallographic and EXAFS studies of the 10-coordinated tripod-La(NO(3))(3) complexes revealed that each La(3+) cation was cooperatively coordinated by one tetradentate tripod and three bidentate NO(3)(-) anions in the crystal and in CH(3)CN. Quantum chemical calculations indicated that the aromatic nitrogen plays a significant role in lanthanide complexation. The experimentally determined stability constants of complexes of the tripod with La(NO(3))(3), Eu(NO(3))(3), and Tb(NO(3))(3) were in good agreement with the theoretically calculated interaction energies. Complexation of each tripod with lanthanide triflate gave a mixture of several lanthanide complex species. Interestingly, the addition of a coordinative NO(3)(-) or Cl(-) anion to the mixture significantly influenced the lanthanide complexation profiles. The particular combination of tripod and a luminescent Eu(3+) center gave anion-selective luminescence enhancements. Pyridine-containing tripods exhibited the highest NO(3)(-) anion-selective luminescence and thus permit naked-eye detection of the NO(3)(-) anion.

Lanthanide Triflate-Catalyzed Arene Acylation. Relation to Classical Friedel–Crafts Acylation

Lanthanide trifluoromethanesulfonates, Ln(OTf) 3 (OTf (-) = trifluoromethanesulfonate), serve as effective precatalysts for the rapid, regioselective, intermolecular acylation of activated arenes. This contribution probes mechanism and metal ionic radius effects in the catalytic lanthanide triflate-mediated acylation of anisole with acetic anhydride. Kinetic studies of Ln(OTf) 3 (Ln = La, Eu, Yb, Lu)-mediated anisole acylation with acetic anhydride in nitromethane reveal the rate law nu approximately k 3 [Ln (3+)] (1)[acetic anhydride] (1)[anisole] (1). Eyring and Arrhenius analyses yield Delta H++ = 12.9 (4) kcal.mol (-1), Delta S++ = -44.8 (1.3) e.u., and E a = 13.1 (4) kcal.mol (-1) for Ln = Yb, with the negative Delta S++ implying a highly organized transition state. The observed primary kinetic isotope effect of k H/ k D = 2.6 +/- 0.15 is consistent with arene C-H bond scission in the turnover-limiting step. The proposed catalytic pathway involves precatalyst formation via interaction of Ln(OTf) 3 with acetic anhydride, followed by Ln (3+)-anisole pi-complexation, substrate-electrophile sigma-complex formation, and turnover-limiting C-H bond scission. Lanthanide size effects on turnover frequencies are consistent with a transition state lacking significant ionic radius-dependent steric constraints. Substrate-Ln (3+) interactions using paramagnetic Gd (3+) and Yb (3+) NMR probes and factors affecting reaction rates such as arene substituent and added LiClO 4 cocatalyst are also explored.

Regioselective green anomeric deacetylation catalyzed by lanthanide triflates

Lanthanide triflates, especially Nd(OTf) 3, efficiently catalyze the regioselective transesterification of anomeric acetates. This method offers an efficient solution for the otherwise difficult removal of methyl uronates anomeric acetates as well as a green alternative to published protocols since the lanthanide catalysts are non-toxic and may be easily recycled and reused.

The structure of the lanthanide aquo ions in solution as studied by 17O NMR spectroscopy and DFT calculations

The (17)O NMR shifts of aqueous samples of lanthanide triflates were measured and analysed. In these systems the triflate anion does not enter the first coordination sphere. The contact contribution to the shifts showed a break at Eu(III), which reflects a change in the number of water molecules in the first coordination sphere of the Ln(III) ion from 9 for La-Sm to 8 for the heavier lanthanides. This change in hydration number is accompanied by a change in the parameters governing the pseudo-contact shifts. Fitting of the data with tricapped trigonal prism and square antiprismatic geometries obtained by DFT (density function theory) calculations showed that the crystal field parameters for these geometries differ by an order of magnitude. The hyperfine coupling constant for both geometries was determined to be A/(Planck's constant)= -4.2 x 10(6) rad s(-1).

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.

Kinetic analysis by DSC of the cationic curing of mixtures of DGEBA and 6,6-dimethyl (4,8-dioxaspiro[2.5]octane-5,7-dione)

The kinetics of the thermal cationic cure reaction of mixtures in different proportions of diglycidylether of bisphenol A (DGEBA) with 6,6-dimethyl (4,8-dioxaspiro[2.5]octane-5,7-dione) (MCP) initiated by ytterbium or lanthanum triflates or using a conventional initiator, BF 3·MEA was investigated. The non-isothermal differential scanning calorimetry (DSC) experiments at a controlled heating rate was used for obtaining the kinetic parameters of the reactive systems. BF 3·MEA and lanthanide triflates initiated curing systems follow a complete different kinetic model. Among lanthanide triflates, ytterbium is the most active initiator.

Rare Earth Triflate Catalysts in the Synthesis of Vitamin E and Its Derivatives

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, please click on HTML or PDF.

Lanthanide Triflate Catalyzed Generation of N‐Acyliminium Ions from α‐Amido Sulfones: The Synthesis of (1‐Alkyl‐1‐aryl)methyl Phenyl Sulfones.

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, please click on HTML or PDF.

Regioselective Strategies Mediated by Lanthanide Triflates for Efficient Assembly of Oligomannans

Readily prepared mannosyl n-pentenylorthoesters (NPOEs) serve as donors in themselves and as convenient intermediates for other glycosyl donors, such as n-pentenyl glycosides (NPGs), thioglycosides, and trichloroacetimidates. These various donors are activated by different reagents, and are therefore amenable to versatile, discriminate use. Scandium and ytterbium triflates respond very differently to these donors, with the result that chemoselective discrimination between NPOEs, NPGs, trichloroacetimidates as well as ethyl and phenyl thioglycosides can be achieved. Appropriate NPOEs are also able to provide 2,6 and 3,6 diol acceptors via rearrangement or glycoside formation, and these can be used for one-pot, sequential glycosidations based on orthogonal donors, and in situ double differential glycosidations. Thus NPOEs activated by iodonium ion, specifically generated from ytterbium triflate/N-iodosuccinimide, can be used to monoglycosidate the diols rapidly, with exquisite regio, and sometimes chemo, selectivity. The residual NPOE is converted into disarmed NPG, which is refractory to the reaction conditions, and so poses no threat to the free-OH of the monoglycosidation product. Further glycosidation of the latter can then achieved by direct addition of a trichloroacetimidate or ethyl thioglycoside. This basic strategy has been used to prepare a branched chain pentadecamannan. The success is an example of the efficiency of donor/acceptor MATCH concept for regioselective glycosylation.

Lanthanide triflates as curing initiators for solid DGEBA resin: Thermal and mechanical characterization

AbstractA new class of cationic initiators, lanthanide triflates, has been studied in the curing of diglycidyl ether of bisphenol‐A (DGEBA). Two metal salts (Erbium and Ytterbium (III) trifluoromethanesulfonate) in various proportions (0.5, 1, and 2 parts per hundred of resin) have been used and the thermal and mechanical properties of the thermosets compared to a common solid epoxy system (crosslinked with o‐tolylbiguanide). The kinetics of these processes has been evaluated by the isoconversional method that has been proved to be an excellent tool to predict the principal curing parameters (conversion/time/temperature). Their mechanical properties have been evaluated by dynamic mechanical thermal analysis (DMTA), stress‐strain curves, impact resistances and adhesion to metallic substrates, and the thermal characteristics were measured by calorimetry (DSC) and thermogravimetry (TGA). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Lanthanide(III) coordination polymers from the exo-coordination of Na +: Syntheses, structures, luminescence, and decay dynamics

[Na 2[Ln 2( sal) 4(CF 3SO 3) 2(H 2O) 4](CF 3SO 3) 2] n Ln = Nd ( 1) and Eu ( 2) were synthesized from the reaction of salicylaldehyde, lanthanide(III) triflates, and sodium hydroxide. The compounds are iso-structural and possess a 2-D supramolecular network built up from discrete dinuclear Ln(III) units [Ln 2( sal) 4(CF 3SO 3) 2(H 2O) 4] via exo-coordination of Na(CF 3SO 3). The sal ligands display μ 2-O coordination modes involving both the phenolic and carbonyl oxygen atoms while the triflates function as both μ 2 and μ 3 bridges. Each Ln(III) in the network is eight coordinate and in bicapped trigonal prism coordination geometry. Luminescence from [Na 2[Eu 2( sal) 4(CF 3SO 3) 2(H 2O) 4](CF 3SO 3) 2] n showed temperature dependent sensitized emission with significant quadrupolar contribution and decay dynamical studies followed single exponential kinetics. Together these results indicate that in the presence of Na + ions, sal, and triflate are useful ligands in the construction of Ln(III) coordination polymers with unusual luminescence and structures.

Compositional variations in monomeric trimethylsilylated allyl lanthanide complexes

Treatment of three equivalents of the potassium salt of the bis(1,3-trimethylsilyl)allyl anion with various late lanthanide triflates (M = Dy, Ho, Er, Tm, Lu) produces the unsolvated triallyllanthanide complexes LnA 3 ′ (A′ = 1,3-(SiMe 3) 2C 3H 3). The use of lanthanide halides (Cl, I) with the potassium allyl also generates neutral complexes, but when lanthanide iodides and the corresponding lithium allyl are combined, the lanthanate species Li(thf) 4 [ LnA 3 ′ I ] are formed. Trends in the bonding of lanthanide allyl complexes with the trimethylsilylated-allyl ligand are explored and compared with those of cyclopentadienyl lanthanide complexes.

FTIR/ATR study of the copolymerization of diglycidyl ether of Bisphenol A with methyl‐substituted γ‐lactones catalyzed by rare earth triflate initiators

AbstractMixtures of DGEBA with γ‐valerolactone (γ‐VL) or α‐methyl‐γ‐butyrolactone (γ‐MBL) 2:1 (mol/mol) were cationically copolymerized in the presence of scandium, ytterbium, or lanthanum triflates as initiators. The evolution of the different reactive groups was followed by means of FTIR/ATR spectroscopy. From these experiments, we could detect the coexistence of two unexpected processes: a reversion of the intermediate spiroorthoester formed to the initial products and a depolymerization process, which only takes place in samples with γ‐VL, when scandium triflate was used as initiator or when the proportion of ytterbium triflate was increased from 1 to 3 phr. When γ‐MBL was used as comonomer no depolymerization occurs which supports the proposed mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2129–2141, 2007

Pybox/Lanthanide‐Catalysed Diels–Alder Reactions with an Unsaturated α‐Oxo Ester or 3‐Alkenoyl‐2‐oxazolidinone as Dienophile: The Sense of Stereoinduction in Five‐ or Six‐Membered Bidentate Reagent Coordination

AbstractThe enantioselective Diels–Alder (DA) reactions of cyclopentadiene with 3‐cinnamoyl‐1,3‐oxazolidinone (3) and methyl (E)‐2‐oxo‐4‐phenyl‐3‐butenoate (4) carried out in the presence of lanthanide triflate complexes of (4′S,5′S)‐2,6‐bis[4′‐(triisopropylsilyloxymethyl)‐5′‐phenyl‐1′,3′‐oxazolin‐2′‐yl]pyridine (1) have been compared. The aim of this work was to compare the effect of the α‐ and β‐dicarbonyl derivatives, coordinated to the cationic site of the catalysts through a five‐ or six‐membered ring chelation, respectively, on the face‐selectivity of the reaction. Only the ScIII triflate complex of 1 was found to be a very selective catalyst in the reaction with cinnamoyloxazolidinone 3, which allowed almost complete stereocontrol. The reaction between cyclopentadiene and methyl keto ester 4 was more complicated because, in addition to the expected normal DA adducts 7 and 8, the less expected endo‐9 product of the [4+2] hetero‐DA (HDA) reaction, which resulted from the α‐keto ester behaving as a heterodiene, was obtained. [3,3] Claisen rearrangement of HDA adduct 9 stereospecifically gave the endo DA product, which allowed a correlation to be made between the absolute configuration of these products. The scandium complex was found to be the best catalyst in both reactions: the DA reaction gave an endo‐7:exo‐8 ratio of 95:5 and the ee of (2R,3R)‐7 was 99.5 %, whereas the HDA reaction was strongly selective and gave a single stereoisomer: (4R,4aS,7aR)‐9 with an ee > 99.5 %. The lanthanum complex furnished the opposite enantiomer in both reactions, albeit with low ee; the lanthanides with intermediate ionic radius gave results that were in between those of scandium and lanthanum. A rationale of the stereochemical outcome is proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Lanthanide triflate catalyzed generation of N-acyliminium ions from α-amido sulfones: the synthesis of (1-alkyl-1-aryl)methyl phenyl sulfones

The reaction of α-amido sulfones with various aromatic and heteroaromatic compounds in the presence of a catalytic amount of lanthanide triflate provides a facile route for the synthesis of (1-alkyl-1-aryl)methyl phenyl sulfones.

Lanthanoid Triflate Catalyzed Preparation of β,β‐Difluorohomopropargyl Alcohols in Aqueous Media. Application to the Synthesis of 4,4‐Difluoroisochromans.

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, please click on HTML or PDF.

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.

The degradation of new thermally degradable thermosets obtained by cationic curing of mixtures of DGEBA and 6,6-dimethyl (4,8-dioxaspiro[2.5]octane-5,7-dione)

The thermal degradation of thermosetting materials prepared by cationic copolymerization of mixtures of different proportions of diglycidylether of bisphenol A (DGEBA) with 6,6-dimethyl (4,8-dioxaspiro[2.5]octane-5,7-dione) (MCP) initiated by ytterbium or lanthanum triflate or using a conventional initiator, BF 3·MEA was investigated. To study the thermal degradation, several techniques were used such as thermogravimetry (TGA), infrared spectroscopy (FTIR) and calorimetry (DSC) and the volatiles evolved during degradation were identified by mass spectrometry. The materials prepared possess the characteristics of thermally degradable thermosets, due to the presence of ester groups in the polymer chain, which are broken at the beginning of degradation. The degradability increased when lanthanide triflates were used in the curing, especially the ytterbium salt and when the proportion of MCP in the material increased.