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31.
32.
Jacobson MA Keresztes I Williard PG 《Journal of the American Chemical Society》2005,127(13):4965-4975
N-Lithio-N-(trialkylsilyl)allylamines can be deprotonated in the presence of ethereal solvents exclusively at the cis-vinylic position to yield 3,N-dilithio-N-(trialkylsilyl)allylamines under mild conditions. Low temperature (1)H and (7)Li NMR ((1)H NOESY, TOCSY, (1)H/(7)Li HSQC, and DO-NMR) studies on the solution structure of 3,N-dilithio-N-(tert-butyldimethylsilyl)allylamine identified three major aggregates in THF (monomer, dimer and tetramer), but the aggregate structures failed to explain the solvent dependence and regiochemical outcome of the reaction. Low temperature (1)H NMR (NOESY, TOCSY, DO-NMR) studies on the solution structure of N-lithio-N-(tert-butyldimethylsilyl)allylamine in the presence of nBuLi identified amide/nBuLi mixed aggregates in both the ethereal solvent THF (1:1 dimer) and the hydrocarbon solvent toluene (1:3 tetramer). Addition of 2 equiv of THF to toluene solutions induces the formation of the same THF solvated 1:1 dimer as observed in neat THF. NMR evidence suggests that in THF the mixed aggregate has close contact between the olefin and the beta-CH(2) of nBuLi, while in the absence of THF, the allyl chain appears to be pointed away from the nearest nBuLi residues. 相似文献
33.
Wolfgang A. Herrmann Carl Krüger Richard Goddard Ivan Bernal 《Journal of organometallic chemistry》1977,140(1):73-89
μ-Carbonylbis(carbonyl-ν5-cycopentadienylrhodium)(Rh—Rh) reacts with N-methyl-and N-ethyl-N-nitrosourea in boiling benzene to yield the dinuclear, diamagnetic, neutral rhodium complexes μ-methylene- (A) and μ-ethylidenebis(carbonyl-η5-cyclopentadienylrhodium)(Rh—Rh) (B), respectively. Deuterium labelled experiments prove the origin of the metal-stabilized methylene ligand to be the alkyl group of the organic precursor. This new method of preparation of transition metal—methylene complexes may be used as an alternative to the commonly used diazo method; the latter method was shown to work with diazodiethylmalonate and dicarbonyl-η5-cyclopentadienylrhodium, the reaction yielding μ-bis(ethoxycarbonyl)methylenebis(carbonyl-η5-cyclopentadienylrhodium)(Rh—Rh).Compound A crystallizes in the triclinic system, P, and with cell constants of a 803.42(5), b 909.98(6), c 938.81(2) pm, α 74.402(3), β81.923(3), and γ 83.685(6)°. The unit cell volume and the calculated density are 651.6 Å3 and 2.069 g cm-3, for one molecule in the asymmetric unit. The molecular geometry of μ-CH2[η5-C5H5Rh(CO)]2 was established from 2718 unique reflections collected with a computer-controlled diffractometer and refined to a final R(F) = 0.0379. The molecular parameters derived from the single-crystal X-ray study conform to a remarkable degree with those found for μ-CO[η5-C5H5Rh(CO)]2. Thus, the bridging ligands CH2 and CO seem to be analogous in their effects on the structural characteristics of the molecular framework of the two molecules. 相似文献
34.
Ivan Ernest 《Helvetica chimica acta》1979,62(8):2681-2694
A synthesis of (6 R, 7 R)-7-acylamino-2-oxocephem-4-carboxylic acids from penicillins is reported based on the formation of the 2-oxocephem system in an intramolecular Wittig condensation. An interesting steric effect of the acylamino grouping on the course of this key step was used to advantage. Some physical and biological properties of this new type of Δ3-cephem are described. 相似文献
35.
Joachim GarricJean-Michel Léger Axelle GrelardMasakazu Ohkita Ivan Huc 《Tetrahedron letters》2003,44(7):1421-1424
X-Ray crystallography and NMR show a strong preference for trans conformers of N′-phenyl or N′-(2-pyridyl) 2-pyridinecarboxylic acid hydrazides, stabilized by an NHNpyr. intramolecular hydrogen bond both in the solid state and in solution. This allows us to extrapolate that oligomers of this unit should adopt extended linear conformations. 相似文献
36.
Silylstannanes can be regioselectively added across terminal alkynes in a quantitative fashion in the presence of a palladium(0) catalyst immobilised in the [bmim]PF6 ionic liquid which can be recycled without loss of activity. 相似文献
37.
Rudovsky J Hermann P Botta M Aime S Lukes I 《Chemical communications (Cambridge, England)》2005,(18):2390-2392
A marked increase of relaxivity has been observed upon rigidifying the internal frame of Gd-containing PAMAM dendrimers: the effect has been attained by either protonation of the dendrimer or by forming supramolecular adducts with cationic polyaminoacids. 相似文献
38.
Reaction of [Nb(NMe(2))(5)] with 10 equiv of 2,6-Me(2)C(6)H(3)SH in toluene results in the formation of red crystals of [Nb(SC(6)H(3)Me(2)-2,6)(5)]. Crystal structure analysis of [Nb(SC(6)H(3)Me(2)-2,6)(5)] showed that the niobium center adopts a distorted trigonal bipyramidal geometry. Niobium disulfide, NbS(2), has been successfully prepared via a thio "sol-gel" process using [Nb(SC(6)H(3)Me(2)-2,6)(5)] as the metal source. In contrast, vapor phase thin-film studies revealed that [Nb(SC(6)H(3)Me(2)-2,6)(5)] functions as a single-source precursor to NbS films. 相似文献
39.
Ivan Gutman Sabina Gojak Niko Radulović Boris Furtula 《Monatshefte für Chemie / Chemical Monthly》2006,137(3):277-284
Summary. In a recent work it was demonstrated that in linear hexagonal chains the distribution of π-electrons into rings (as computed
by means of the Randić–Balaban method) is uniform, irrespective of the nature of the terminal fragments. We now establish that an analogous, yet somewhat
more complex, uniformity in the π-electron distribution exists also in double linear hexagonal chains, as well as in some
other benzenoid systems. 相似文献
40.
James D. Korp Ivan Bernal Steven F. Watkins F. R. Fronczek 《Journal of heterocyclic chemistry》1982,19(3):459-462
The molecular structure of 10-(1,3-Dithiolan-2-ylidene)-10H-indeno[1,2-f] -1,2,3,4,5-pentathiepin S7C12H89 has been determined by single crystal X-ray diffraction. The crystals are triclinic, space group PI, with two molecules in a unit cell of dimensions α = 8.931(2), b = 9.387(2), c = 10.175(2) Å, α = 75.73(2), β = 73.35(1), γ = 64.37(2)°. The structure was solved by direct methods, and refined to a final R value of 3.3% for 1925 independent reflections. The molecule consists of an indene core with a nearly co-planar dithiolane and a fused pentasulfide chain. The S5C2 ring is in the chair configuration, with an average S? S distance of 2.052 Å. There is no variation of bond lengths as is frequently seen in multi-sulfur chains. The indenone ring shows no evidence of any delocalization, while the dithiolane ring is disordered at the two methylene positions. No attempt was made to resolve the disorder, since it is frequently seen and has been thoroughly investigated previously. 相似文献