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1.
An oxidovanadium(IV) complex having a perrhenato ligand [VO(ReO4)(4,4′-tBubpy)2][0.25SO4·0.5ReO4] (4,4′-tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine) efficiently catalyzes not only dehydrogenative oxidation of benzylic and propargylic mono-alcohols but also oxidative CC bond cleavage of meso-1,2-diaryl-1,2-ethanediols under atmospheric molecular oxygen, affording the corresponding carbonyl compounds in good yield.  相似文献   

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The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G7 basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (rg and ∠α) of caffeine are as follows: <r(NC)ring> = 1.382(3) Å; r(CC) = 1.382(←) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; <r(NCmethyl)> = 1.459(13) Å; <r(CO)> = 1.206(5) Å; <r(CH)> = 1.085(11) Å; ∠N1C2N3 = 116.5(11)°; ∠N3C4C5 = 121. 5(13)°; ∠C4C5C6 = 122.9(10)°; ∠C4C5N7 = 104.7(14)°; ∠N9–C4=C5 = 111.6(10)°; <∠NCHmethyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one.  相似文献   

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A general and efficient procedure for the stereoselective synthesis of (E)-(1-propenyl)phenyl esters from readily accessible allylphenols has been developed. The process involves a two-step sequence consisting of the initial acylation of the allylphenols with an acid chloride, followed by catalytic CC bond isomerization in the resulting allylphenyl esters. The latter step was performed in methanol at 80 °C using catalytic amounts (0.5 mol %) of the commercially available bis(allyl)-ruthenium(IV) dimer [{RuCl(μ-Cl)(η33-C10H16)}2] (C10H16=2,7-dimethylocta-2,6-diene-1,8-diyl). Reactions proceeded in high yields (68–93%) and short times (4–9 h) with complete E-selectivity.  相似文献   

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The synthesis of new ruthenium-based catalysts applicable for both homogeneous and heterogeneous metathesis is described. Starting from the Hoveyda-Grubbs first generation (1) and the Hoveyda-Grubbs second generation (2) catalysts the homogeneous catalysts [RuCl((RO)3Si–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(SIMes)] (4: R = Et, R′ = H; 5: R = R′ = Me) (SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) were prepared by substitution of one chloride ligand with trialkoxysilyl functionalized silver carboxylates (RO)3Si–C3H6–N(R′)–CO–C3F6–COOAg (3a: R = Et, R′ = H; 3b: R = R′ = Me). These homogeneous ruthenium-species are among a few known examples with mixed anionic ligands. Exchange of both chloride ligands afforded the catalysts [Ru((RO)3Si–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(SIMes)] (9: R = Et, R′ = H; 11: R = R′ = Me) and [Ru((RO)3Si–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(PCy3)] (8: R = Et, R′ = H; 10: R = R′ = Me). The reactivity of the new complexes was tested in homogeneous ring-closing metathesis (RCM) of N,N-diallyl-p-toluenesulfonamide and TONs of up to 5000 were achieved. Heterogeneous catalysts were obtained by reaction of 4, 5 and 811 with silica gel (SG-60). The resultant supported catalysts 4a, 5a, 8a11a showed reduced activity compared to their homogenous analogues, but rival the activity of similar heterogeneous systems.  相似文献   

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From thermal analyses and X-ray diffraction the phase diagram of the BiSnTe and SnTeBi2Te3 sections was determined. The local environment of Sn and Te atoms was studied by 119Sn and 125Te Mössbauer spectroscopy. The BiSnTe section showed a eutectic reaction at 267 °C and 20 % mole SnTe–80 % mole Bi. No intermediate compound was detected. The SnTeBi2Te3 section is characterized by a eutectic reaction at 585 °C and 40 % mole SnTe–60% mole Bi2Te3 and a peritectic reaction at 600 °C and 50 % mole SnTe–50% mole Bi2Te3. It corresponds to the compound SnBi2Te4, which has a rhombohedral layered structure with unit cell parameters a=4.3954(4) Å and c=41.606(1) Å. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASSnTe / Bi / Bi2Te3 / phase diagram / Mössbauer  相似文献   

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SnO prepared by soft chemistry exhibits a black color and semiconducting properties. The X-ray diffraction indicates a tetragonal symmetry (SG: P4/nmm) with nano crystallites of an average size of 85 nm. The forbidden band, determined from the diffuse reflectance is found to be 1.46 eV. The electrical conductivity occurs by polaron hopping and follows an Arrhenius type law with activation energy of 0.21 eV, the change in the slope at 526 K is attributed to the oxidation to SnO2. The photo-electrochemical study shows n type conduction with a flat band potential of ?0.45 V, close to the photocurrent onset potential (?0.40 V). The electrochemical impedance spectroscopy shows the bulk contribution of SnO (Rb = 1.7  cm2) and decreases down to 1.89  cm2 under illumination. The photocatalytic properties have been evaluated for the first time for to the oxygen evolution. The valence band, deriving from Sn2+: 5p orbital with a potential (?0.80 VSCE/5.55 eV), is suitably positioned with respect to O2/H2O level (~0.6 VSCE), leading to water oxidation under visible light. The best performance occurs at pH  7 with an oxygen liberation rate of 23 µmol mL h?1 (mg catalyst)?1 and a quantum efficiency of 1.2%. An improvement of ~13% is observed on the system SnO/clay.  相似文献   

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《Comptes Rendus Chimie》2015,18(5):554-557
The direct three-component condensation of resorcinol, 1-(2,4-dihydroxyphenyl)ethanone or 2,4-dihydroxybenzophenone with benzaldehydes and malononitrile to generate some novel 2-amino-3-cyano-4H-chromene derivatives has been carried out over K2CO3 (25 mol%) with high efficiency in water as a green solvent at 70 °C.  相似文献   

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