Showing papers on "Tetrahydrofuran published in 1989"

The Mechanism of Phase Separation of Polymers in Organic Media—Apolar and Polar Systems

Abstract: The phase separation properties of nine apolar and 15 polar systems, each comprising two polymers dissolved in one organic solvent, were examined in the light of recent developments in surface thermodynamics of polar components. A clear correlation existed between the sign of the total interfacial free energy of interaction of the system and the phase separation (or miscibility). Conversely, some of the phase separation results could be used to estimate the electron-donor surface tension parameters of methyl ethyl ketone and tetrahydrofuran.

Lewis base adducts of uranium triiodide: A new class of synthetically useful precursors for trivalent uranium chemistry

Abstract: A series of organic-solvent-soluble Lewis base adducts of uranium triiodide that are easy to prepare and that serve as excellent precursors to a variety of new and known trivalent uranium compounds have been found. The compound UI{sub 3}(THF){sub 4} (THF = tetrahydrofuran) has been prepared by the reaction of clean uranium turnings with freshly sublimed elemental iodine in THF solution at 0{degree}C. Single crystals of UI{sub 3}(THF){sub 4} have been grown from a concentrated THF solution at -40{degree}C, and the structural data collected from x-ray diffraction studies at 23{degree}C are reported. 31 refs., 1 fig.

Solvation of anion radicals: gas-phase versus solution

Abstract: Reversible half-wave potentials for 38 neutral/anion radical couples have been measured at 298 K by cyclic voltammetry in five solvents: tetrahydrofuran, N,N-dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide, and methanol. Among the compounds are 22 substituted nitrobenzenes and nine quinones. The potentials are referenced to the cobaltocenium/cobaltocene couple

Scandium, yttrium, uranium, and thorium derivatives of the 1,4-bis(trimethylsilyl)cyclo-octatetraene dianion; the X-ray crystal structure of [Sc2(η-C8H6{1,4-(SiMe3)2})2(µ-Cl)2(µ-thf)](thf = tetrahydrofuran)

Abstract: Deprotonation of 1,4-bis(trimethylsilyl)cyclo-octa-2,5,7-triene affords the 1,4-bis(trimethylsilyl)cyclo-octatetraene dianion, which reacts with [UCl4] or [ThCl4] to give the sandwich compounds [M(η-C8H6{1,4-(SiMe3)2})2], M = U or Th, with [UCl2(BH4)2] to give [U(η-C8H6{1,4-(SiMe3)2})(η3-BH4)2], and with [ScCl3(thf)3] or [YCl3(thf)3](thf = tetrahydrofuran) to yield [{M(η-C8H6{1,4-(SiMe3)2})(η-Cl)}2{thf}n], M = Sc, n= 1; M = Y, n= 2; X-ray crystallography shows the latter scandium compound to possess a novel semi-bridging thf ligand.

Four-and five-co-ordinate lanthanide (II) aryloxides: X-ray structures of the bis(2,6-di-t-butyl-4-methylphenoxo)ytterbium(II) complexes [Yb(OAr)2(L)2] and [Yb(OAr)2(L′)3][ArC6H2But2-2,6-Me-4, L = tetrahydrofuran (thf) or OEt2, L′= thf]

Abstract: General methods for the preparation of hydrocarbon-soluble, monomeric ytterbium (II) aryloxides are described {Yb+2TIOAr, or [Yb(NR2)2(OEt2)2]+2ArOH;RSiMe3, ArC6H2But2-2,6-Me-4; crystalline [Yb(OAr)2(thf)3](thf = tetrahydrofuran)(1) has the unprecedented square-pyramidal YbII stereochemistry (one thf apical), whereas the complexes [Yb(Oar)2(L)2][L = thf (2) or OEt2(3)] are tetrahedral, with 2.207 (12)(1), 2.137(10)(2), or 2.154(28)A(3); complex (3) with thf readily yields (1) or (2)}.

Preparation of the bis(trimethylsilyl)amido lanthanide chlorides [{Ln[N(SiMe3)2]2(µ-Cl)(thf)}2](thf = tetrahydrofuran), and the crystal and molecular structures of the gadolinium and ytterbium complexes

Abstract: Reaction of LnCl3 with 2 equivalents of LiL [L = N(SiMe3)2] in tetrahydrofuran (thf) at –5 °C yields [{LnL2Cl(thf)}2] for Ln = Eu, Gd, or Yb or [YL2Cl(thf)2] for Ln = Y. X-Ray crystal structure analysis of the compounds of Gd and Yb confirms the formation of halide-bridged dimers. In the M2Cl2 bridging unit the M–Cl bond lengths differ slightly and the angle at the metal (ca. 74°) is much smaller than at chlorine (ca. 106°). The metal co-ordination geometries are irregular but can be best described as distorted trigonal bipyramidal with the bridging chlorines spanning one axial and one equatorial site. The bond lengths M–Cl and M–N indicate a Gd–Yb radius difference of ca. 0.07 A, but the M–O distances differ by 0.093 A. Variable-temperature n.m.r. studies of [{EuL2Cl(thf)}2] and [{YbL2Cl(thf)}2] show that there is free rotation about Ln–N and Ln–O bonds at room temperature. These rotations are frozen out at low temperatures to give a solution structure having higher symmetry (C2h) than that found in the crystal.

The crystal structure of bis{tris(trimethylsilyl)methyl}magnesium: an example of two-co-ordinate magnesium in the solid state

Abstract: The lithium–magnesium complex [Li(thf)2(µ-Br)2Mg{C(SiMe3)3}thf](thf = tetrahydrofuran) decomposes of heating in vacuum to give [Mg{C(SiMe3)3}2], which is monomeric; this is the first characterisation of a two-co-ordinate magnesium compound in the solid state.

One-pot synthesis of tetrahydrofuran derivatives from allylic alcohols and vinyl ethers by means of palladium(II) acetate.

Abstract: Reaction of allylic alcohol with vinyl ether in the presence of Pd(OAc)2 afforded furan derivatives in good yield. Pd(OAc)2 was essential for the reaction. PdCl2 complex did not afford cyclized product but gave acetal exclusively. Three components were combined at once to produce 4-(3-butenyl)-2-butoxy-4-methyltetrahydrofuran upon treatment of a mixture of 2-methyl-2-propen-1-ol, butyl vinyl ether, and allyl bromide. The reaction could successfully be extended to the synthesis of nitrogen containing heterocycles by use of N-tosyl allylic amines in place of allylic alcohols.

Molekül- und Kristallstruktur des 1,4-Bis[tris(tetrahydrofuran)lithium]-octaphenyltetrasilans

Abstract: Das aus Octaphenyl-cyclo-tetrasilan und Lithium in Tetrahydrofuran (THF) dargestellte, orangerote 1,4-Dilithium-octaphenyltetrasilan [4] kristallisiert aus Tetrahydrofuran/n-Pentan als Addukt mit sechs Molekulen Tetrahydrofuran triklin in der Raumgruppe P1. Die Verbindung weist folgende, bei −5 ± 3°C bestimmte Parameter der Elementarzelle auf: a = 1159,6(3); b = 1268,4(2); c = 1367,8(3) pm; α = 92,23(2)°; β = 113,79(2)° γ = 111,62(2)°; Z = 1. Nach den Ergebnissen einer Rontgenstrukturanalyse (Rw = 0,046) liegt ein zentrosymmetrisches Molekul mit gestrecktem, planarem LiSi4Li-Gerust vor; jedes Lithium ist an Silicium und die Sauerstoffatome aus drei Tetrahydrofuran-Molekulen gebunden. Charakteristische Bindungslangen und -winkel sind: LiSi 271; SiSi 241 und 243; SiC 190 bis 192 pm; LiSiSi 126°; SiSiSi 127°. 29Si- und 7Li-Kernresonanz-Messungen bei tiefen Temperaturen ergeben in Losung drei unterschiedliche Addukte. Molecular and Crystal Structure of 1,4-Bis[tris(tetrahydrofuran)lithium]-octaphenyltetrasilane 1,4-Dilithium-octaphenyltetrasilane prepared from octaphenyl-cyclo-tetrasilane and lithium in tetrahydrofuran (THF) [4], can be isolated from tetrahydrofuran/n-pentane as an adduct with six molecules of tetrahydrofuran per formula unit. The orange-red compound crystallizes in the triclinic space group P1 {a = 1159.6(3); b = 1268.4(2); c = 1367.8(3) pm; α = 92,23(2)° β = 113.79(2)° γ = 111.62(2)° at −5 ± 3°C; Z = 1}. An x-ray structure determination (Rw = 0.046) shows the existence of a centrosymmetric molecule with an extended planar LiSi4Li unit; either lithium atom is bound to silicon and to the oxygen atoms of three molecules of tetrahydrofuran. Characteristic bond lengths and angles are: LiSi 271; SiSi 241 and 243; SiC 190 to 192 pm; LiSiSi 126°; SiSiSi 127°. 29Si and 7Li n.m.r. measurements at low temperatures indicate the presence of three different adducts.

Selective lanthanide-catalysed reactions: catalytic properties of Sm and Yb metal vapour deposition products

Abstract: The characteristics of lanthanide catalysts obtained when Sm and Yb were vaporized into a frozen organic (tetrahydrofuran, benzene and methyl-cyclohexane) matrix (77 K) were investigated. These low-valent, highly dispersed lanthanide particles (indicated as Sm/THF, Sm/benzene, Yb/THF, Yb/benzene etc.) were catalytically active and selective for hydrogenation and isomerization. Samarium usually showed a greater activity than ytterbium. Olefin [ethene, propene, but-1-ene and (z)-but-2-ene] hydrogenation obeyed the rate law v=kPH, suggesting that the reaction is controlled by catalytic activation of hydrogen. The molecular isotopic identity of hydrogen was conserved during the hydrogenation. Yb/THF and Yb/benzene were active for partial hydrogenation of benzene to cyclohexene. For the hydrogenation of olefins and acetylenes the substrate specificity was high; thus C—C double bonds were more readily reduced than triple bonds. The samarium and ytterbium catalysts discriminate between terminal and internal C—C triple bonds, only internal CC bonds (but-2-yne and pent-2-yne) being reduced very selectively in contrast to acetylene, methylacetylene and but-1-yne. Solid base character of the lanthanide provides a cause for these differences in catalytic properties.