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Tetrahydrofuran

About: Tetrahydrofuran is a research topic. Over the lifetime, 11778 publications have been published within this topic receiving 158241 citations. The topic is also known as: diethylene oxide & 1,4-epoxybutane.


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Journal ArticleDOI
TL;DR: In this article, Thomson et al. showed that the organometallic chemistry of scandium compounds can be improved with two bulky pentamethylcyclopentadienyl groups as ancillary ligands.
Abstract: The use of two bulky pentamethylcyclopentadienyl groups has allowed the preparation of highly coordinatively unsaturated monomeric derivatives of scandium. The chloride, methyl, benzyl, and phenyl derivatives are described. An unstable hydride derivative is obtained via hydrogenation of the alkyls. Spectral data for the methyl derivative together with the results of an X—ray structure determination suggest that the methyl group is bonded to scandium in a conventional manner; in particular, no agostic Sc-H—C interaction is indicated. H—D exchange between H2, benzene, [C5(CH3)5], Si(CH3)4, P(CH3)3, CH, and the n—CR bonds of tetrahydrofuran is catalyzed by the hydride derivative. The C—H bonds of cyclohexane and the —CH bonds of tetrahydrofuran are unreactive. With pyridine an a-metallated pyridine derivative is obtained, whose structure is reported. These hydride and methyl derivatives rapidly polymerize ethylene, whereas propene and isobutene undergo insertion to yield first n—alkyl scandium derivative followed by insertion into the vinylic C—H bonds of additional olefin to afford alkane and scandium alkenyls. Some speculation on the mechanisms of these unusual transformations is presented. INTRODUCTION The organometallic chemistry of the elements of the first transition series (TiCu) has been extensively investigated during the past three decades. The remaining member, scandium, has been virtually ignored. Its classification as a true transition element is somewhat debatable, and scandium has been traditionally grouped with yttrium, and lanthanum, and the lanthanide elements (CeLu), On the other hand, the ionic radius of Sc3+ is closer to those of some of the early transition metal ions (1) in some of their common oxidation states: III IV V Sc3+ Ti V3+ 0.81 A 0.68 A 0.78 A Zr Nb3+ 0.93 A 0.80 A 0.86 A La3+... Lu3+ Hf Ta3+ 1.15 A 0.93 A 0.81 A 0.86 A Thus, the organometallic chemistry of scandium may be expected apriori to be intermediate between that of the early transition elements and that of yttrium and the later lanthanide elements. Our research group has a longstanding interest in the organometallic chemistry of the group IV transition elements. We have found that monomeric, coordinatively unsaturated alkyls and hydrides may be obtained with two bulky pentamethylcyclopentadienyl groups as ancillary ligands, i.e. 2 M. E. THOMPSON and J. E. BERCAW (M = Ti, Zr, Hf; R, R' = H, alkyl) The high reactivity of these toward CU, olef ins, H2, and C—H bonds is attributed in large part to the fact that the formally d0,16—electron metal center is a strong Lewis acid; entering substrates interaet strongly with the vacant la1 orbital (2) of the bent sandwich complex. It occurred to us that monomeric hydride and alkyl derivatives of scandocene may exhibit even greater Lewis acidity; scandium is more electropositive and Cp2Sc—R (R = H, alkyl) derivatives are d°, 14—electron species with two low—lying vacant orbitals. Organoscandium compounds are commonly polymeric {Sc(C6H5)31X (3), [Sc(CECC6H5)3Jx (3), and [Sc(C5H5)3]x (4), dimeric [(5—C5H5)2ScClJ2 (5))or are associated with a main group III compound (,g. Cri5—C5E5)2Sc(i—CH3)2Al(CH3)2(6) and {-CsH3(SiNe3)2}2Sc(—H)2BH2 (7)). Monomeric species may be obtained as adducts with Lewis bases (fl5—C5H5)2Sc(CH3)(B), B = THF, pyridine) (8). Hence, highly coordinatively unsaturated organoscandium compounds are indeed voracious Lewis acids which tightly bind bases, or, in their absence, oligomerize with bridging halide or alkyl groups. In these regards, organoscandium compounds resemble organic compounds of the main group III element aluminum. Bulky ancillary ligands often impede oligomerization of coordinatively unsaturated species and render them more soluble, Recently Lappert and. co—workers have adopted this strategy in the preparation of hydrocarbon soluble bis(cyclopentadienyl)scandium derivatives [{fl5—C5HS(SiMeg)2}2ScC1}2 (9) and 5—C5H3(SiNe3)2}2Sc(p-H)2BH2). In order to obtain monomeric, base—free organoscandium we have undertaken the syntheses of derivatives containing two sterically more demanding pentamethylcyclopentadienyl groups as ancillary ligands: Sc—'R (R = hydride, alkyl, aryl, etc.) These formally d°, 14—electron compounds are extremely reactive, undergoing facile reactions with olefins, H2, and C—H bonds*. We report herein the preparation and characterization of these compounds and some aspects of their chemistry. RESULTS AND DISCUSSION Prparation of Alkyl and Hydride Derivatives of Permethylscandocene The requisite starting material, (r15—C5Ne5)2ScCl (1), is prepared straightforwardly form ScCl3(THF)3 (THF = tetrahydrofuran) and Li(C5Ne5) in ref luxing xylenes (eq 1). The product is obtained in 75% yield by direct sublimation from the residue following removal of solvent ScCl3(THF)3 + 2 Li(C5Ne5) (q5-C5Ne5)2ScC1(THF) + 2 THF + 2 LiCl

133 citations

Journal ArticleDOI
04 Jun 2007-Small
TL;DR: Treatment of solutions of P2 in tetrahydrofuran (THF), a nonselective solvent, with increasing amounts of solvents that are selective for the polar polythiophene blocks (water) or the nonpolar polyfluorene blocks (hexane), respectively, results in the formation of two different types of core-shell aggregates, which show rather different optical properties.
Abstract: A novel, amphiphilic, conjugated block copolymer is described, which was prepared by a Suzuki-type cross-coupling of 2-bromo-[9,9-bis(2-ethylhexyl)fluorene]-7-pinacolato boronate as an AB-type monomer and monobromo-substituted poly[3-(6-bromohexyl)thiophene] (Br-P3BrHT) as a polymeric end capper in the key step. PF-P3PHT (P2; PF = poly(9,9-dialkylfluorene); P3PHT = poly[3-(6-diethylphosphonato-hexyl)thiophene]) as the amphiphilic target polymer was then generated in a polymer-analogous conversion of the alkyl bromide side chains of the PF-P3BrHT (P1) precursor into polar alkyl phosphonate groups by reaction with triethyl phosphite. P2 shows a strong influence of the solvent polarity on the optical spectra (absorption, emission). Treatment of solutions of P2 in tetrahydrofuran (THF), a nonselective solvent, with increasing amounts of solvents that are selective for the polar polythiophene blocks (water) or the nonpolar polyfluorene blocks (hexane), respectively, results in the formation of two different types of core-shell aggregates, which show rather different optical properties (photoluminescence quenching, excitation energy transfer).

133 citations

Journal ArticleDOI
TL;DR: In this paper, the authors showed that tetrahydrofuran clathrate hydrate single crystals grow from the supercooled melt as octahedra, showing that {1 1 1} is the slowest growing face.

132 citations

Journal ArticleDOI
TL;DR: In this paper, the properties and possible structures for the compounds are discussed, and the compound C5H5Fe(CO)2I is also described, as well as possible structures of the compounds.

132 citations

Journal ArticleDOI
TL;DR: The phase behavior of alkyl carboxylic acid/water/tetrahydrofuran (THF) ternary systems as a function of component concentration, pH, ionic strength, and temperature was investigated and the coacervates were described for the first time.
Abstract: Coacervates made up of alkanoic (C8−C16) and alkenoic (C18) acid reverse micelles were described for the first time, and their potential for the extraction of organic compounds prior to liquid chromatography was examined. The coacervation process occurred in miscible binary mixtures of water and a variety of protic and aprotic solvents. The phase behavior of alkyl carboxylic acids was found to be a function of both the Hildebrand solubility parameter, δ, and the hydrogen-bonding capability of the solvent. The best solvents for analytical extractions were those featuring the lowest δ values. The phase behavior of alkyl carboxylic acid/water/tetrahydrofuran (THF) ternary systems as a function of component concentration, pH, ionic strength, and temperature was investigated. The efficiency and the time required for phase separation depended on the experimental procedure used (i.e., standing, centrifugation, stirring, and sonication). The formation of alkyl carboxylic acid reverse micelles in THF was proven us...

132 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023194
2022382
2021124
2020154
2019193
2018218