- A novel approach to RE-OR bond from in situ reaction of rare earth triflates and sodium alkoxides: A versatile catalyst for living ring-opening polymerization of ε-caprolactone
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A series of rare earth triflates (RE(OTf)3, RE = Sc, Y and Lu) were used for the first time as moisture-stable precursors to generate rare earth alkoxide complexes through an in situ reaction with sodium alkoxides (NaOR) in tetrahydrofuran. 1H NMR and 13C NMR results confirmed the fast ligands exchange process and the formation of rare earth-oxygen (RE-OR) bond. The in situ formed catalysts displayed high reactivity toward living ring-opening polymerization (ROP) of ε-caprolactone (CL). For instance, Lu(OTf)3/sodium isopropoxide (NaOiPr)-catalyzed ROP of CL with the [CL]0/[NaO iPr]0/[Lu(OTf)3]0 feeding ratio of 300/3/1 produced poly(ε-caprolactone) (PCL) with controlled molecular weight (Mn,exp = 11.9 kDa vs Mn,theo = 11.8 kDa) and narrow polydispersity (PDI) of 1.08 within 3 min at 25°C. The kinetic studies and chain extension confirmed the controlled/living nature for the Lu(OTf)3/NaOiPr-catalyzed ROP of CL. In addition, end-functionalized PCLs bearing vinyl or alkynyl group with narrow PDIs were obtained by using functional sodium alkoxides in the presence of Lu(OTf) 3. 1H NMR and MALDI-ToF MS analyses of the obtained PCLs clearly indicated the presence of the residue of OR groups at the chain ends. A coordination-insertion polymerization mechanism was proposed including a fast ligand exchange between Lu(OTf)3 and NaOR giving the respective lutetium alkoxide complexes, and a CL insertion into RE-OR bond via acyl-oxygen cleavage.
- You, Lixin,Shen, Zhiquan,Kong, Jie,Ling, Jun
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- Electrochemical trifluoromethylation of isonicotinic acid hydrazide using cyclic voltammetry and galvanostatic electrolysis
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Trifluoromethylation of isonicotinic acid hydrazide has been investigated in trifluoroacetic acid containing pyridine, triethylamine and sodium trifluoroacetate dissolved in acetonitrile on platinum and glassy carbon electrodes using cyclic voltammetry. L
- Raja Beryl,Joseph Raj
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- New method of beta-NaYF4: Yb3+, Er3+ synthesis by using beta-cyclodextrin
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Abstract The novel method of synthesis of the hexagonal modification beta-NaYF4 doped with Yb3+ (17 at.%) and Er3+ (3 at.%) using beta-cyclodextrin is proposed. Complex fluorides were prepared by decomposition of the mixture of metal fluoroacetates hydrates with and without addition of beta-cyclodextrin and were investigated by X-ray diffraction, energy dispersive X-ray analysis, scanning and transmission electron microscopy. The samples prepared by adding beta-cyclodextrin in the reaction mixture are single phase and have a hexagonal structure. At the same time, decomposition of the mixture of metal trifluoroacetates hydrates without beta-cyclodextrin is accompanied by pyrohydrolysis, leading to a contamination of the products by impurities of yttrium oxyfluorides and sodium fluoride. So a new synthetic approach proposed in this work allows to obtain pure complex fluorides with homogeneous distribution of elements and with homogeneous pore distribution.
- Fedorova, Anna A.,Fedulin, Andrey I.,Morozov, Igor V.
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- Strategic synthesis of [Cu2], [Cu4] and [Cu5] complexes: inhibition and triggering of ligand arm hydrolysis and self-aggregation by chosen ancillary bridges
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The Schiff base ligand HL1 ({2,6-bis(allylimino)methyl}-4-methylphenol) having no coordinating donor arm has been examined for its reaction medium and ancillary bridge dependent reactivity for a hierarchical family of CuII complexes. The ligand showed a unique reactivity pattern toward CuII in solution. The bridging nature of in situ generated HO? ions in the absence and presence of externally added carboxylates (RCOO?; R = CF3, C6H5 and CH3) has been utilized to produce complexes {[Cu2(μ-L2)2(H2O)]2[Cu2(μ-L2)2(H2O)2](ClO4)6} (1) (HL2 = 3-{(allylimino)methyl}-2-hydroxy-5-methylbenzaldehyde), [Cu4(μ4-O)(μ-L1)2(μ1,3-O2CCF3)4] (2), [Cu4(μ4-O)(μ-L1)2(μ1,3-O2CC6H5)4]·H2O (3), and [Cu5(μ3-OH)2(μ-L1)2(μ1,3-OAc)2(OAc)2(H2O)4][Cu5(μ3-OH)2(μ-L1)2(μ1,3-OAc)2(OAc)3(H2O)](ClO4)3·2C2H5OH (4). The absence of carboxylate anions did not yield HO? ions in situ and triggered single ligand arm hydrolysis. The formation of tetra- and pentanuclear aggregates as well as ligand hydrolyzed dinuclear products has been rationalized to identify the possible roles of carboxylate anions in solution. Detailed characterization of the complexes in the solid state and in solution has been carried out using spectroscopic measurements, X-ray crystallography, variable temperature magnetic measurements and functional behavior. In MeOH solutions at 298 K, the complexes 1-4 showed catalytic oxidation of 3,5-di-tert-butyl catechol (3,5-DTBCH2) saturated with O2 from the air.
- Das, Manisha,Canaj, Angelos B.,Bertolasi, Valerio,Murrie, Mark,Ray, Debashis
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- Heterometallic trinuclear oxo-centered clusters as single-source precursors for synthesis of stoichiometric monodisperse transition metal ferrite nanocrystals
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The use of heterobimetallic metal complexes as molecular single-source precursors is a promising strategy for the targeted synthesis of phase-pure stoichiometric ternary metal oxide nanocrystals. However, the design and synthesis of these precursors is not trivial and can require considerable effort. Using spinel metal ferrite nanocrystals of formula MFe2O4 (M = Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) as a model system, this paper evaluates the efficacy of the single-source precursor approach by comparing directly nanocrystals synthesized from the solvothermal reaction of heterobimetallic trinuclear oxo-bridged clusters of formula MIIFeIII2(μ3-O)(μ2-O2CR)6(H2O)3, R = CF3 to nanocrystals synthesized from the solvothermal reaction of stoichiometric mixtures of multi-source precursors, such as metal acetate or nitrate salts. For each M explored here, the clusters form phase-pure MFe2O4 nanocrystals with significantly narrower size distributions than nanocrystals synthesized from multi-source-precursors. In the case of M = Cu, the multi-source metal salt precursors produce a mixture of CuO and CuFe2O4. Additionally, changing the electronic nature of the R-group on the bridging carboxylate ligand from electron withdrawing (CF3) to electron donating (CH3 or C(CH3)3) decreases the average diameter of the resulting nanocrystals by a factor of two. The cluster molecules therefore offer superior control over both morphology and composition for transition metal ferrite nanocrystals. We hypothesize that this remarkable performance arises from the presence of pre-formed M2+-O-Fe3+ moieties in the cluster molecules that enable direct nucleation of MFe2O4 and preclude nucleation of binary oxide impurities.
- Brennessel, William W.,Knowles, Kathryn E.,Sanchez-Lievanos, Karla R.,Tariq, Mehrin
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- Oxidation of fluoroalkyl alcohols using sodium hypochlorite pentahydrate [1]
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Fluoroalkyl alcohols are effectivity oxidized to the corresponding fluoroalkyl carbonyl compounds by reaction with sodium hypochlorite pentahydrate in acetonitrile in the presence of acid and nitroxyl radical catalysts. Although the reaction proceeded slower under a nitroxyl radical catalyst- free condition, the desired carbonyl compounds were obtained in high yields. For the reaction with fluoroalkyl allylic alcohols, the corresponding α,β-epoxyketone hydrates were obtained in high yields.
- Kirihara, Masayuki,Suzuki, Katsuya,Nakakura, Kana,Saito, Katsuya,Nakamura, Riho,Tujimoto, Kazuki,Sakamoto, Yugo,Kikkawa, You,Shimazu, Hideo,Kimura, Yoshikazu
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- Alkali metal trifluoroacetates for the nucleophilic trifluoromethylation of fullerenes
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Fullerene C60 readily reacts with potassium and cesium trifluoroacetates yielding C60(CF3)–M+ salts, and subsequent acid hydrolysis gives ortho-C60(CF3)H. The reaction rate and the probability of the alternative reaction pathways strongly depend on the particular metal cation. Thus, the reactivity increases in the order Li 2- rather than CF3-functionalization of the fullerene, in good accordance with the hard/soft acids and bases theory. The nucleophilic trifluoromethylation is found to be applicable to other pristine fullerenes like C70 as well as to fullerene derivatives like p7mp-C70(CF3)10. It enables selective preparation of low trifluoromethylated fullerenes via regioselective consecutive trifluoromethylation under accurately controlled solution-phase conditions.
- Bogdanov, Viktor P.,Dmitrieva, Veronika A.,Ioutsi, Vitaliy A.,Belov, Nikita M.,Goryunkov, Alexey A.
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- Pyrolytic decarboxylation of some derivatives of perfluorinated mono- and dicarboxylic acids
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Pathways of pyrolysis of perfluorinated carboxylic acids are considered in relation to the structure of the acids and reaction conditions. The reaction mechanism is discussed.
- Lebedev,Berenblit,Starobin,Gubanov
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p. 1640 - 1645
(2007/10/03)
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- Reaction of polyfluoro-3-chloro(bromo)-1-butenes with sodium hypohalites and properties of epoxides derived therefrom
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Epoxidation of 3-chloro(bromo)heptafluoro-1-butenes and 3,4-dichlorohexafluoro-1-butene with aqueous solutions of sodium hypohalites is accompanied by cleavage of the carbon skeleton at the double bond and formation of polyfluorocarboxylic acid sodium sal
- Zapevalov,Filyakova,Kodess,Saloutin
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p. 919 - 923
(2007/10/03)
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- 1,2 chemiluminescent dioxetanes of improved performance
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A new class of stable dioxetanes bears a polycyclic stabilizing group and aryloxy moiety, the oxygen atom of which is provided with a protective group which can be removed by an enzymatic or chemical trigger admixed with the dioxetane. The polycyclic stabilizing group is preferably spiroadamantane. The group further bears an alkoxy, aryloxy, aralkyloxy or cycloalkyloxy moiety which is partially or completely substituted with halogens, particularly fluorine and chlorine. Proper selection of electron active groups on the stabilizing moiety, the aryl group and the OR group yields enhanced enzyme kinetics, superior light intensity and excellent detection sensitivity in various assays.
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- Synthesis and some properties of 1-chloro(bromo)heptafluoro-1-butenes and their epoxy derivatives
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1-Chloro- and 1-bromoheptafluoro-1-butenes have been synthesized by chlorination (bromination) of 1,2,3,3,4,4,4-heptafluoro-1-butene and subsequent dehydrohalogenation of the resulting 1,2-dichloro-and 1,2-dibromo-l,2,3,3,4,4,4-heptafluorobutanes with aqueous alkali. 1-Chloro- and l-bromo-l,2-epoxy-heptafluorobutanes have been obtained by oxidation of the title alkenes with molecular oxygen under UV irradiation. In the presence of fluoride ion, the epoxy derivatives undergo isomerization into α-chloro(bromo)-hexafluorobutyryl fluorides; the reaction with antimony pentafluoride yields 1-chloro(bromo)-heptafluoro-2-butanones.
- Filyakova,Kodess,Zapevalov
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p. 1256 - 1262
(2007/10/03)
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- Production of carboxylic acid halides and carboxylate salts
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A process for preparing carboxylic acid halides and carboxylate salts by reacting metal or "onium" halides with carboxylic anhydrides, which process is very suitable for working-up anhydrous, spent catalyst preparations. The resulting carboxylic acid halide or carboxylate salt can be used as an acylating reagent or alkylating reagent, and metal halide or "onium" halide liberated during this can be reacted anew with carboxylic anhydride and regenerated, thereby making it possible to effect a hydrolysis-free alkylation or acylation without forming salt-type waste products. If the mixture of carboxylic acid halide and carboxylate salt is allowed to react with an alcohol, preferably in situ, the resulting ester can be isolated without hydrolysis.
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- α- AND β-CHLORO(BROMO)-2,3-EPOXYPOLYFLUOROBUTANES. FORMATION AND CHEMICAL TRANSFORMATIONS
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It was shown that the epoxidation of polyfluoro-2-butenes containing chlorine or bromine atoms at the α or β position with sodium hypochlorite has lower selectivity than the reaction with internal perfluoroalkenes.The reactions of chlorine and bromine-containing 2,3-epoxypolyfluorobutanes with a series of nucleophilic and electrophilic reagents were conducted.It was noticed that the opening of their epoxide ring by antimony pentafluoride is accompanied by migration of the chlorine or bromine atom.With nucleophilic reagents the ring of 1-chloro- and 1-bromo-2,3-epoxyheptafluorobutanes opens in both possible directions.
- Filyakova, T. I.,Matochkina, E. G.,Peschanskii, N. V.,Kodess, M. I.,Zapevalov, A. Ya.
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- HYDROLYSIS OF FLUOROALKYL-CONTAINING β-AMINOVINYL KETONES
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The kinetics of hydrolysis of fluoroalkyl-containing β-aminovinyl ketones R1C(O)CHC(NHR3)R2, in which the substituents CF3 and HCF2CF2 are in the ketone (R1) or enamine parts of the molecule (R2), was studied.In acid (pH 10) media, they hydrolyze with the formation of the corresponding amines and β-diketones.In an alkaline medium, the β-diketones undergo cleavage to fluorinated acids and methyl ketones.The rate constants of hydrolysis in an acid medium change within a range of four orders, depensdng on the nature of the substituents.The presence of a fluoroalkyl group at the enamine reaction center increases the hydrolysis rate.In an alkaline medium, the rate constants vary within one order.
- Bazhenova, L. N.,Filyakova, V. I.,Kirichenko, V. E.,Pashkevich, K. I.
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p. 581 - 585
(2007/10/02)
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- METAL SILANOLATES: ORGANIC SOLUBLE EQUIVALENTS FOR O-2
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Alkali metal trimethylsilanolates, M+ -OSiMe3, convert carboxylic acid derivatives into their corresponding anhydrous acid salts under mild non-aqueous conditions.
- Langanis, E. D.,Chenard, B. L.
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p. 5831 - 5834
(2007/10/02)
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- SYNTHESIS OF PERFLUOROBICYCLIC ETHERS . THE ELECTROCHEMICAL FLUORINATION OF α-CYCLOHEXENYL-SUBSTITUTED CARBOXYLIC ACID DERIVATIVES
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The electrochemical fluorination of α-cyclohexenyl-substituted carboxylic esters afforded both perfluoro (9-alkyl-7-oxa-bicyclononane)s and perfluoro(8-alkoxy-9-alkyl-7-oxabicyclononane)s in fairly good yields.As the driving force for the ring-closure in this fluorination, a mechanism which involves a resonance stabilized intermediate radical is proposed. Perfluoro(8-chloro-8-methoxy-9-ethyl-7-oxabicyclononane) and perfluoro(8,8-dichloro-9-ethyl-7-oxabicyclononane) were obtained by the controlled chlorination of perfluoro(8-methoxy-9-ethyl-7-oxabicyclo nonane) with anhydrous aluminum chloride in low yields.Some new fused perfluorobicyclic ethers and a perfluoroacid fluoride obtained in this experiment have been characterized by infrared, mass and 19F nmr spectra and elemental analysis.
- Abe, Takashi,Hayashi, Eiji,Baba, Hajime,Nagase, Shunji
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p. 419 - 434
(2007/10/02)
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