Études calorimétriques en milieu solvant organique IV. Dissociation de LiAlH4 dans le tétrahydrofuranne

From calorimetric measurements a model of solution is proposed for LiAlH₄ in THF. It is ionised as LiAlH₄ ? Li⁺ + AlH^?₄. For this reaction, ΔH_i = 3.05 kcal mol^?1 and the dissociation constant is K = 0.11.     

The formation and molecular structure of acetylcyclopentadienylsodium-tetrahydrofuranate

Acetylcyclopentadienylsodium has been isolated in crystalline form as a THF adduct from a reaction between cyclopentadienylsodium and methyl acetate in THF solution. The product has been characterized by means of a single-crystal X-ray diffraction study. {[C₅H₄CMeO]Na·THF}_n crystallizes in the monoclinic space group P2₁/c with unit cell parameters a 6.698(3), b 16.095(4), c 10.661(3) Å, β 92.93(3)° and D_c 1.17 g cm^?3 for Z = 4. Least-squares refinement led to a final R value of 0.080 based on 661 independent observed reflections. The coordination sphere around each sodium atom consists of the oxygen atoms from two C₅H₄CMeO ligands, the oxygen atom of the THF molecule, and an ion contact pair between the sodium and the five ring carbon atoms of the C₅H₄CMeO ligand.     

The formation and molecular structure of (η5-C5H5)3Sm · OC4H8

Reaction of 1/2 mole ratio of (η⁵-C₅H₅)SmCl₂ ·3THF and NaCCCH₂OCH₂CHCH₂ in THF solution resulted in the formation of (η⁵-C₅H₅)Sm·OC₄H₈; the complex crystallizes in monoclinic space group P2₁/n with unit cell constants a = 8.254(5), b = 24.63(1), c = 8.339(3) Å, β = 101.33(5)° and D_c = 1.67 g/cm³ for Z = 4. Refinement has led to a final R value of 0.041 based on 2106 independent observed reflections. The THF molecule is coordinated to the samarium atom at a SmO distance of 2.522(6) Å. The SmC(cyclopentadienyl) bond lengths range from 2.70(1) to 2.80(1) Å and average 2.742(1) Å. A comparison of some significant structural parameters along the isostructural series (η⁵-C₅H₅)₃Ln·THF (LnLa, Pr, Nd, Gd, Dy, Lu and Sm) with the ionic radii of Ln³⁺ was made.     

Influence of MgCl2 on Grignard reagent composition in tetrahydrofuran. III

Reaction of [MgCl₂(THF)₂] with [NBu₄][BF₄] yields the compounds [NBu₄][MgCl₄] (IV) and [Mg(THF)₆][BF₄]₂ (V). After addition of dioxane the reaction equilibrium shifts in the opposite direction. The formation of [MgCl₂(C₄H₈O₂)₂] in solution does not require the presence of MgCl₂. This compound may be formed in the reaction of dioxane with the ionic or molecular species formed by the magnesium atom in solution. The [NBu₄][BF₄] salt also reacts with the Grignard reagent to produce compound IV which confirms that there is a new equilibrium between [Mg(R)X(THF)_n] and [MgR₂(THF)₂], [MgCl₄]²⁻ and [Mg(THF)₆]²⁺. Bis(tetrahydrofuran)magnesium dichloride, because of its reactivity is only stable in Grignard reagent. For that reason the composition of the Grignard reagent in solution is best described as an equilibrium between [Mg(R)X(THF)_n] and [(THF)₄Mg(μ-Cl)₂MgR₂] and [RMg₂(μ-Cl)₃(THF)₅] rather than as a Schlenk equilibrium.     

3-exo-tet Cyclization of 2,2-disubstituted 1,3-dihalopropanes with indium in aqueous and ionic liquid solvent system

The 3-exo-tet cyclization of 2,2-disubstituted 1,3-dihalopropanes with In powder in THF solution of 20% H₂O, dioxane solution of 20% H₂O, and ionic liquids, such as [bmim]Br, [bmim]Cl, and [bmin]BF₄, respectively, was efficiently carried out to form the corresponding 1,1-disubstituted cyclopropanes in good yields. The cyclopropanation of 2,2-disubstituted 1,3-dihalopropanes with In powder in ionic liquids, such as [bmim]Br, [bmim]Cl, and [bmin]BF₄, was markedly accelerated compared with that in a THF solution of 20% H₂O and a dioxane solution of 20% H₂O. The mechanism was proposed to involve the radical 3-exo-tet cyclization of the formed 3-halopropyl radical.     

Actinide arene-metalates: ion pairing effects on the electronic structure of unsupported uranium–arenide sandwich complexes

Addition of [UI₂(THF)₃(μ-OMe)]₂·THF (2·THF) to THF solutions containing 6 equiv. of K[C₁₄H₁₀] generates the heteroleptic dimeric complexes [K(18-crown-6)(THF)₂]₂[U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]₂·4THF (118C6·4THF) and {[K(THF)₃][U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]}₂ (1THF) upon crystallization of the products in THF in the presence or absence of 18-crown-6, respectively. Both 118C6·4THF and 1THF are thermally stable in the solid-state at room temperature; however, after crystallization, they become insoluble in THF or DME solutions and instead gradually decompose upon standing. X-ray diffraction analysis reveals 118C6·4THF and 1THF to be structurally similar, possessing uranium centres sandwiched between bent anthracenide ligands of mixed tetrahapto and hexahapto ligation modes. Yet, the two complexes are distinguished by the close contact potassium-arenide ion pairing that is seen in 1THF but absent in 118C6·4THF, which is observed to have a significant effect on the electronic characteristics of the two complexes. Structural analysis, SQUID magnetometry data, XANES spectral characterization, and computational analyses are generally consistent with U(iv) formal assignments for the metal centres in both 118C6·4THF and 1THF, though noticeable differences are detected between the two species. For instance, the effective magnetic moment of 1THF (3.74 μ_B) is significantly lower than that of 118C6·4THF (4.40 μ_B) at 300 K. Furthermore, the XANES data shows the U L_III-edge absorption energy for 1THF to be 0.9 eV higher than that of 118C6·4THF, suggestive of more oxidized metal centres in the former. Of note, CASSCF calculations on the model complex {[U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]₂}²⁻ (1*) shows highly polarized uranium–arenide interactions defined by π-type bonds where the metal contributions are primarily comprised by the 6d-orbitals (7.3 ± 0.6%) with minor participation from the 5f-orbitals (1.5 ± 0.5%). These unique complexes provide new insights into actinide–arenide bonding interactions and show the sensitivity of the electronic structures of the uranium atoms to coordination sphere effects.

Use of Chatt metal-arene protocols with uranium leads to the synthesis of the first well-characterized, unsupported actinide–arenide sandwich complexes. The electronic structures of the actinide centres show a key sensitivity to ion pairing effects.     

Crystallographic characterisation of novel Zn(II) silsesquioxane complexes and their application as initiators for the production of polylactide

Herein, the solid state structures of the products from the reaction of the silsesquioxane triol (iso-C₄H₉)₇Si₇O₁₂(OH)₃ (1) with two equivalents of ZnMe₂ in both THF and toluene are reported. In both cases tetrametallic Zn(II) complexes were isolated, with toluene [(iso-C₄H₉)₇Si₇O₁₂]₂Zn₄Me₂ (2) was prepared while performing the reaction in THF the analogous complex [(iso-C₄H₉)₇Si₇O₁₂]₂Zn₄Me₂(THF)₂ (3) was formed. Both species have also been characterised via¹H, ¹³C{¹H} and ²⁹Si{¹H} NMR spectroscopy, which confirm the solid state structures are maintained in solution. Both 2 and 3 show modest activities for the polymerisation of rac-lactide and a heterogeneous catalyst has also been prepared.     

Synthesis and some properties of Nd(B11H14)3 · 4Dg (Dg is diglyme)

The reaction of Nd(BH₄)₃ · 3THF with decaborane-14 in diglyme at 85–90°C yields Nd(B₁₁H₁₄)₃ · 4Dg. The duration of the reaction is 20 h. The molar ratio of Nd(BH₄)₃ · 3THF to B₁₀H₁₄ is is 1 :3.5. The product is precipitated with heptane from a diglyme solution. The yield is 70%. In an inert atmosphere, Nd(B₁₁H₁₄)₃ · 4Dg is stable to 150°C and decomposes with an exotherm at 160–190°C. The IR spectrum of Nd(B₁₁H₁₄)₃ · 4Dg in the region of B-H stretching vibrations contains an intense band at 2530 cm^?1. The ¹¹B {¹H} NMR spectra of the synthesized compound in diglyme solutions contain signals of the tetradecahydro-nido-undecaborate anion B₁₁H ₁₄ ^? (δ = -14.0, -15.6, and -16.5 ppm).     

[{(η5-C5H4CH3)2YbIII(OC4H8)}(μ2-O)]: Ein neuer Lanthanoid (Ln)-Komplex mit streng linearer LnOLn-Anordnung

Light-green, well-shaped crystals of the new binuclear complex: [{(η⁵-C₅H₄CH₃)₂Yb^III(THF)}₂(μ-O)] (1), incidentally obtained from a solution of (C₅H₄CH₃)₃Yb^III in tetrahydrofuran (THF) in the presence of glyoxal-bis(tert-butylimine), have been subjected to a single-crystal X-ray diffraction study. The crystals are monoclinic, with space group P2₁/c and a 1110.4(2), b 862.3(1), c 1628.0(3) pm; β 104.69(1)°; R = 0.047 (R_w = 0.051). The YbO distance of 201.5(1) pm within the strictly linear YbOYb skeleton belongs to the shortest LnO bonds (Ln = lanthanoid element) so far observed.     

Solution-phase synthesis of ordered mesoporous carbon as resonant-gravimetric sensing material for room-temperature H_2S detection

H_2S can cause multiple diseases and poses a great threat to human health.However,the precise detection of extremely toxic H_2S at room temperature is still a great challenge.Here,a facile solvent evaporation induced aggregating assembly(EIAA) method has been applied for the production of ordered mesoporous carbon(OMCs) in an acidic THF/H_2 O solution with high-molecular-weight poly(ethylene oxide)-b-polystyrene(PEO-b-PS) copolymers as the structure-directing agent,formaldehyde and resorcinol as carbon precursors.Along with the continuous evaporation of THF from the mixed solution,cylindrical micelles are formed in the solution and further assemble into highly ordered mesostructure.The obtained OMCs possesses a two-dimensional(2 D) hexagonal mesostructure with uniform and large pore diameter(～19.2 nm),high surface area(599 m~2/g),and large pore volume(0.92 cm~3/g).When being used as the resonant cantilever gas sensor for room-temperature H_2S detection,the OMCs has delivered not only a superior gas sensing performance with ultrafast re s ponse(14 s) and recovery(21 s) even at low concentration(2 ppm) but also an excellent selectivity toward H_2S among various common interfering gases.Moreover,the limit of detection is better than 0.2 ppm,indicating its potential application in environmental monitoring and health protection.     

Photo-induced homolysis of alkyltricyclopentadienyluranium(IV) complexes: an example of a successful UIV → UIII reduction

Photo-induced reduction of two organouranium complexes of the type Cp₃UR (R = CH₃ and n-C₄H₉) was studied in toluene and THF solution at various temperatures. Optimal conditions for the production of Cp₃U . THF as the final product involve UV/VIS irradiation in THF at ca. 60°C. Spin trap experiments indicate that, at least in THF, intermediate free radicals participate. The results, including gas chromatographic, mass spectroscopic and ¹H NMR spectroscopic measurements, are discussed in terms of a virtually first order multi-step process involving discrete radical pairs kept together efficiently by solvent cages so that H-atom abstraction from a Cp ligand followed by decomposition of the organometallic product is largely avoided.     

Pentazol‐Derivate und daraus entstehende Azide: [O3S—p‐C6H4—N5]— und [O3S—p‐C6H4—N3]— als Kalium‐Kronenether‐Salze

Pentazole Derivates and Azides Formed from them: Potassium‐Crown‐Ether Salts of [O₃S—p‐C₆H₄—N₅]^— and [O₃S—p‐C₆H₄—N₃]^{— —}O₃S—p‐C₆H₄—N₂⁺ was reacted with sodium azide at —50 °C in methanol, yielding a mixture of 4‐pentazolylbenzenesulfonate and 4‐azidobenzenesulfonate (amount‐of‐substance ratio 27:73 according to NMR). By addition of KOH in methanol at —50 °C a mixture of the potassium salts K[O₃S—p‐C₆H₄—N₅] and K[O₃S—p‐C₆H₄—N₃] was precipitated (ratio 60:40). A solution of this mixture along with 18‐crown‐6 in tetrahydrofurane yielded the crystalline pentazole derivate [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₅]·THF by addition of petrol ether at —70 °C. From the same solution upon evaporation and redissolution in THF/petrol ether the crystalline azide [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·THF was obtained. A solution of the latter in chloroform/toluene under air yielded [K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·1/3H₂O. According to their X‐ray crystal structure determinations [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₅]·THF and [THF‐K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·THF have the same kind of crystal packing. Differences worth mentioning exist only for the atomic positions of the pentazole ring as compared to the azido group and for one THF molecule which is coordinated to the potassium ion; different orientations of the THF molecule take account for the different space requirements of the N₅ and the N₃ group. In [K‐18‐crown‐6][O₃S—p‐C₆H₄—N₃]·1/3H₂O there exists one unit consisting of one [K‐18‐crown‐6]⁺ and one [O₃S‐C₆H₄—N₃]^— ion and another unit consisting of two [O₃S‐C₆H₄—N₃]^— ions joined via two [K‐18‐crown‐6]⁺ ions and one water molecule. The rate constants for the decomposition [O₃S‐C₆H₄—N₅]^— → [O₃S‐C₆H₄—N₃]^— + N₂ in methanol were determined at 0 °C and —20 °C.     

Synthesis,structure, and catalytic activity of rare-earth metal amides with a neutral pyrrolyl-functionalized indolyl ligand

<正>1 Representation of complexes and selected bond distances and bond angles Figure S1 Structure of complex 4. Hydrogen atoms were omitted for clarity, ellipsoids set at the 30% probability level. Selected bond distances() and angles(°): Er(1)–Cl(1) 2.6180(18), Er(1)–N(1) 2.301(6), Er(1)–N(4) 2.232(6), Er(1)–N(5) 2.229(6), N(1)–Er(1)–Cl(1) 87.41(14), N(4)–Er(1)–Cl(1) 101.16(14), N(5)–Er(1)–Cl(1) 118.60(16), N(4)–Er(1)–N(1) 114.1(2), N(5)–Er(1)–N(1) 108.7(2), N(5)–Er(1)–N(4) 121.9(2).Figure S2 Structure of complex 5. Hydrogen atoms were omitted for clarity, ellipsoids set at the 30% probability level. Selected bond distances(o) and angles(°): Y(1)–Cl(1) 2.6212(12), Y(1)–N(1) 2.280(3), Y(1)–N(4) 2.214(3), Y(1)–N(5) 2.228(3), N(1)–Y(1)–Cl(1) 87.67(8), N(4)–Y(1)–Cl(1) 121.32(8), N(5)–Y(1)–Cl(1) 102.88(8), N(4)–Y(1)–N(1) 107.75(11), N(5)–Y(1)–N(1) 111.64(11), N(4)–Y(1)–N(5) 120.78(10).     

Preparation and reactions of the (dicarbonyl)(η5-cyclopentadienyl)(tetrahydrofuran)iron cation: A convenient route to (dicarbonyl)(η5-cyclopentadiemyl)(η2-olefin)iron cations and related complexes

The versatile reagent [η⁵-C₅H₅)Fe(CO)₂(THF)]BF₄ has been isolated from the reaction of (η₅-C₅H₅)Fe(CO)₂I and AgBF₄ in THF and shown to react in CH₂Cl₂ with olefins to yield [(η⁵-C₅H₅)Fe(CO)₂(η²-olefin)]BF₄ complexes. For most olefins the yields are high. The yield in these reactions can be increased by treating the CH₂Cl₂ solution of [(η⁵-C₅H₅)Fe(Co)₂(THF)]BF₄ and olefin with gaseous BF₃ in order to complex the THF as the BF₃-THF adduct. Most striking is the increase in yield for the cyclohexene complex from 17% to 92%.     

Studies on organolanthanide complexes: VII. Formation and cleavage of carbon-metal bonds of dicyclopentadienyl-early lanthanide complexes

Four new 1,10-phenanthroline-coordinated early lanthanide complexes containing a σ-carbon-metal bond 1–4 were synthesized by the reaction of alkynylsodium or alkyllithium with (η⁵-C₅H₅)₂LnCl·nPhen in THF at 0 or −78°C. The complexes (η⁵-C₅H₅)₂LnCl·nPhen were prepared from LnCl₃·nPhen and C₅H₅Na. 1,1′-Trimethylenedicyclopentadienyl(phenylacetylenylneodymium). THF 5 was also prepared. These complexes were identified by elemental analysis, IR, ¹H NMR spectroscopy and thermogravimetry. Protolysis reactions of these complexes with H₂O. CH₃OH and t-C₄H₉OH show that different protolytic reagents give the products with different cleavage extents of σ- and π-bonds. The ligands in the complexes also affect the cleavage of π-bonds. β-Hydrogen elimination of complex 3 takes place with thermal decomposition.     

Derivatives of cyclooctatetraenecyclopentadienyl-titanium containing substituents in the five-membered ring

The syntheses of some substituted cyclooctatetraenecyclopentadienyl-titanium compounds are described, viz: (h⁸-C₈H₈)(h⁵-R)Ti with R = C₅H₄CH₃, C₅H₄C(CH₃)₃, C₅H₄Si(CH₃)₃, indenyl (= Ind) and fluorenyl (= Flu). The compounds have been prepared by reaction of [(h⁸-C₈H₈)TiCl·THF]₂ with RNa in ether solution. The paramagnetic compounds are thermally stable to ca. 350°, but they are sensitive to air and water. The IR spectra and dipole moments of the compounds are given. The mass spectra of the complexes (h⁸-C₈H₈)(h⁵-C₅H₅)Ti, (h⁸-C₈H₈)(h⁵-Ind)Ti and (h⁸-C₈H₈)(h⁵-Flu)Ti indicate weakening of the Tih⁵R bond-strength in this sequence.     

Synthesis and characterisation of sterically bulky lithium amidinate and bis-amidinate complexes

The synthesis and characterisation of the amidines, (tript)C(NR)(NHR), R = Prⁱ or cyclohexyl (Cy), tript = triptycenyl, and lithium amidinate complexes, [Li(THF)₂{(tript)C(NR)₂}] bearing the bulky triptycenyl substituent on the amidine or amidinate backbone carbon is described. NMR spectroscopic studies have shown these to exist solely as their Z-syn isomeric forms in solution due to the steric effect of the triptycenyl moiety. The X-ray crystal structures of two examples confirm this is also the case in the solid state. A new bis-amidine ligand, 1,4-{(PrⁱHN)(PrⁱN)C}₂{2,3,5,6-C₆(p-C₆H₄Bu^t)₄}, and the corresponding lithium bis-amidinate complex, [1,4-{Li(THF)₂(PrⁱN)₂C}₂{2,3,5,6-C₆(p-C₆H₄Bu^t)₄}], which incorporate a sterically bulky tetraarylphenylene spacer unit have also been prepared. In solution, the amidine undergoes facile inter-conversion between its E-syn:E-syn and Z-syn:E-syn isomers. The bis-amidinate complex has been structurally characterised and shown to chelate both of its lithium centres.     

Synthesis,characterization, and structures of arylaluminum reagents and asymmetric arylation of aldehydes catalyzed by a titanium complex of an N-sulfonylated amino alcohol

A series of phenylaluminum reagents AlPh_xEt_3?x(L) (x = 1–3) containing adduct ligand L [Et₂O, THF, OPPh₃, or 4-dimethylaminopyridine (DMAP)] were synthesized and characterized. NMR studies showed that AlPh_xEt_3?x(L) (x = 1 or 2) exists as an equilibrium mixture of 3–4 species in solution. Solid-state structures of the phenylaluminum reagents reveal a distorted tetrahedral geometry. Asymmetric additions of phenylaluminum to 2-chlorobenzaldehyde were examined employing a titanium(IV) complex [TiL¹(OPrⁱ)₂]₂ 10 (H₂L¹ = (1R,2S)-2-(p-tolylsulfonylamino)-1,3-diphenyl-1-propanol) as a catalyst precursor. It was found that the adduct ligand L had a strong influence on the reactivity and the enantioselectivity in asymmetric phenyl additions to aldehydes. The phenylaluminum reagents with OPPh₃ or DMAP were unreactive toward aldehydes, and AlPh₃(THF) was found to be superior to AlPh₃(OEt₂) or AlPhEt₂(THF). Asymmetric aryl additions of AlAr₃(THF) to aldehydes employing a loading of 5 mol % titanium(IV) complex 10 with a strategy of a slow addition of the aldehydes over 20 min were conducted, and the reactions produced optically active secondary alcohols in high yields with excellent enantioselectivities of up to 94% ee.     

Reaction of a naphthalene complex C10H8Yb(THF)2 with cyclopentadienyl-substituted alcohols and amines as a convenient synthetic route to the half-sandwich complexes of divalent ytterbium

The reactions of ytterbium naphthalene complex C₁₀H₈Yb(THF)₂ with 2-cyclopentadienylethanol, 1-cyclopentadienylpropan-2-ol, 3-cyclopentadienyl-1-butoxypropan-2-ol, and cyclopentadienyldimethylsilyl-tert-butylamine were studied. The bivalent ytterbium complexes with chelate bifunctional cyclopentadienyl ligands [(η⁵−C₅H₅)CH₂CH₂(η¹−O)]Yb(THF), [(η⁵−C₅H₅)CH₂CH₂(η¹−O)]Yb(DME). [(η⁵−C₅H₅)CH₂CH(Me)(η¹−O)]Yb(THF), [(η⁵−C₅H₅)CH₂CH(CH₂OC₄H₉)(η¹−O)]Yb(THF), and [(η⁵−C₅H₅)SiMe₂(η¹−N(Bu¹))]Yb(THF) were obtained and characterized. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 742–745, April, 2000.