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排序方式: 共有196条查询结果,搜索用时 15 毫秒
61.
Hydrosilylation of aromatic nitriles promoted by solvated rhodium atom-derived catalysts 总被引:1,自引:0,他引:1
Anna Maria Caporusso Nicoletta Panziera Paolo Pertici Emanuela Pitzalis Piero Salvadori Giovanni Vitulli Gianmario Martra 《Journal of molecular catalysis. A, Chemical》1999,150(1-2):275-285
Rhodium metal particles, isolated as supported or unsupported powder starting from mesitylene solvated rhodium atoms, catalyse the hydrosilylation of aromatic nitriles to N,N-disilylamines in high conversion at 100°C. Different hydrosilanes (HSiMe3, HSi(OEt)3) can be employed. In the case of cinnamonitrile, the chemoselectivity of the reaction to 2-trimethylsilyl-3-phenylpropionitrile and (E)- and (Z)-1-di(trimethylsilyl)amino-3-phenyl-1-propene is strongly dependent on the reaction temperature. The commercial rhodium on γ-Al2O3 catalyst is considerably less active and selective than the analogous catalyst prepared via Metal Vapour Synthesis (MVS) probably owing to the different dimension and distribution of the metal particles in the two samples as shown by HRTEM analysis. 相似文献
62.
63.
Paola Antoniotti Stefano Borocci Nicoletta Bronzolino Felice Grandinetti 《Chemphyschem》2004,5(9):1345-1351
The structure and stability of various HCN2+ isomeric structures have been investigated at the complete active space SCF (CASSCF) and multireference-configuration interaction [MR-Cl-SD(Q)] levels of theory with the 6-31G(d) and 6-311G(d,p) basis sets. The investigated species include the singlet (S) and triplet (T) open-chain H-N-C-N+ ions 1S, 1S', and 1T, the open-chain H-C-N-N+ ions 2S, 2S', and 2T, the HC-N2+ cyclic structures 3S and 3T, and the HN-CN+ cyclic structures 4S and 4T. All these species have been identified as true energy minima on the CASSCF(8,7)/6-31G(d) potential energy surface, and their optimised geometries, refined at the CASSCF(8,8)/6-31G(d) level of theory, have been used to perform single point calculations at the [MR-Cl-SD(Q]/6-311G(d,p) computational level. The most stable structure was the H-N-C-N+ ion 1T, whose absolute enthalpy of formation at 298.15 K has been estimated as 333.9 +/- 2 kcalmol(-1) using the Gaussian-3 (G3) procedure. The two species closest in energy to 1T are the triplet H-C-N-N+ ion 2T and the singlet diazirinyl cation 3S, whose G3 enthalpies of formation at 298.15 K are 343.5 +/- 2 and 340.6 +/- 2 kcalmol(-1), respectively. Finally, we have discussed the implications of our calculations for the detailed structure of the HCN2+ ions formed in the reaction between N3+ and HCN, experimentally observed by flowing after-glow-selected ion flow/drift tube mass spectrometry and possibly occurring in Titan's atmosphere. 相似文献
64.
Stefano Borocci Nicoletta Bronzolino Felice Grandinetti 《Helvetica chimica acta》2007,90(7):1335-1352
Ab initio calculations at the MP2 level of theory disclose the conceivable existence of neutral complexes containing four or five distinct noble gases (Ng) each bound to a distinct Be‐atom. These multicenter polynuclear Ng molecules are formally obtained by replacing the H‐atoms of CH4 and but‐2‐yne with ? NBeNg moieties, which behave as independent monovalent ‘functional groups’. Our investigated complexes include the five homotetranuclear [C(NBeNg)4] complexes 1 – 5 (Ng=He? Xe), the five heterotetranuclear complexes [CN4Be4(He)(Ne)(Ar)(Kr)] ( 6 ), [CN4Be4(He)(Ne)(Ar)(Xe)] ( 7 ), [CN4Be4(He)(Ne)(Kr)(Xe)] ( 8 ), [CN4Be4(He)(Ar)(Kr)(Xe)] ( 9 ), and [CN4Be4(Ne)(Ar)(Kr)(Xe)] ( 10 ), and the heteropentanuclear complex [HC4N5Be5(He)(Ne)(Ar)(Kr)(Xe)] ( 11 ). We also investigated the five model complexes [H3CNBeNg] (Ng=He? Xe) containing a single ? NBeNg moiety. The geometries and vibrational frequencies of all these species, invariably characterized as minimum‐energy structures, were computed at the MP2(full)/6‐31G(d,p)/SDD level of theory, and their stability with respect to the loss of the various Ng‐atoms was evaluated by single‐point calculations at the MP2(full)/6‐311G(d)/SDD level of theory. The beryllium‐Ng binding energies range from ca. 17 (Ng=He) to ca. 63 (Ng=Xe) kJ/mol, and the results of natural‐bond‐orbital (NBO) and atoms‐in‐molecules (AIM) analysis reveal that the Be? Ng interaction is essentially electrostatic for helium, neon, argon, and krypton, and has probably a small covalent contribution for xenon. 相似文献
65.
Marvelli L Mantovani N Marchi A Rossi R Brugnati M Peruzzini M Barbaro P de los Rios I Bertolasi V 《Dalton transactions (Cambridge, England : 2003)》2004,(5):713-722
A family of new Fischer-type rhenium(III) benzoyldiazenido-2-oxacyclocarbenes of formula [(ReCl2[eta1-N2C(O)Ph][=C(CH2)nCH(R)O](PPh3)2][n = 2, R = H (2), R = Me (3); n = 3, R = H (4), R = Me (5)] have been prepared by reaction of [ReCl2[eta2-N2C(Ph)O](PPh3)2] (1) with omega-alkynols, such as 3-butyn-1-ol, 4-pentyn-1-ol, 4-pentyn-2-ol, 5-hexyn-2-ol in refluxing THF. The correct formulation of the carbene derivatives 2-5 has been unambiguously determined in solution by NMR analysis and confirmed for compounds 2-4 by X-ray diffraction methods in the solid state. All complexes are octahedral with the benzoyldiazenido ligand, Re[N2C(O)Ph], adopting a "single bent" conformation. The coordination basal plane is completed by an oxacyclocarbene ligand and two chlorine atoms. Two triphenylphosphines in trans positions with respect to each other complete the octahedral geometry around rhenium. The reactivity of 1 towards different alkynes and alkenes including propargyl- and allylamine has been also studied. With propargyl amine, monosubstituted or bisubstituted complexes, [(ReCl2[eta1-N2C(O)Ph][eta1-NH2CH2C triple bond CH]n(PPh3)(3-n)][n= 1 (6); n = 2 (7)], have been isolated depending on the reaction conditions. In contrast, the reaction with allylamine gave only the disubstituted complex [(ReCl2[eta1-N2C(O)Ph][eta1-NH2CH2CH=CH2]2(PPh3)] (8). The molecular structure of the monosubstituted adduct has been confirmed by X-ray analysis in the solid state. 相似文献
66.
Francesco A. Bottino Giovanna DiPasquale Nicoletta Leonardi Antonino Pollicino 《Journal of polymer science. Part A, Polymer chemistry》1995,33(5):843-847
A series of new poly(arylene ether)s, containing naphthalene, pyridine, and quinoline units have been prepared by solution condensation polymerization. The synthesis involves nucleophilic displacement of aromatic dihalides with aromatic potassium bisphenates in an anhydrous dipolar aprotic solvent at elevated temperatures. The polymers, having inherent viscosity from 0.24 to 1.32 dL/g, were obtained in quantitative yield, have excellent thermal stability as shown by 10% weight loss temperatures in nitrogen and air (above 450 and 430°C, respectively) and high glass transition temperatures (in the range of 150–220°C). The introduction of quinoline moieties in the polymer backbone positively influences the thermal properties, such as high Tg/Tm ratios. © 1995 John Wiley & Sons, Inc. 相似文献
67.
The dissociation constants of the two oxime groups of 1,1-bis(pyridinium-4-aldoxime)trimethylene dibromide (TMB-4) were determined using spectrophotometric data. Two numerical methods were applied to treat the overlapping equilibria. The results obtained by both agreed with each other and their mean values at 25°C corrected for the ionic strength of 0.05moldm–3 are pKa1=7.49±0.11 and pKa2=8.96±0.09. These values were discussed in terms of the pKas of 1,1-bis(pyridinium-4-aldoxime)oxydimethylene dichloride (Toxogonin), a similar dioxime, which were derived by extrapolation of literature data. 相似文献
68.
Maurizio Galimberti Nicoletta Mascellani Fabrizio Piemontesi Isabella Camurati 《Macromolecular rapid communications》1999,20(4):214-218
Ethene/propene copolymerizations were performed in solution with a single centre catalyst system composed of a “constrained geometry” half‐sandwich organometallic complex {η1: η5‐[(tert‐butylamido)dimethylsilyl](2,3,4,5‐tetramethyl‐1‐cyclopentadienyl)}titanium dichloride, and methylaluminoxane. The statistical treatment of polymerization data allowed to determine the reactivity ratios for ethene and propene: rE = 1.35 ± 0.09, rP = 0.82 ± 0.05, rErP = 1.10 ± 0.14. This catalyst system promotes an almost random distribution of ethene and propene and gives rise to values of rP and rE very similar to each other. 相似文献
69.
Evidence for PSII donor-side damage and photoinhibition induced by cadmium treatment on rice (Oryza sativa L.) 总被引:2,自引:0,他引:2
Pagliano C Raviolo M Dalla Vecchia F Gabbrielli R Gonnelli C Rascio N Barbato R La Rocca N 《Journal of photochemistry and photobiology. B, Biology》2006,84(1):70-78
The effects of cadmium (from 7.5 to 75 microM) on chloroplasts of rice were studied at the structural and biochemical level. Loss of pigments, reduction of thylakoids and decrease in oxygen evolution and Fv/Fm ratio occur in leaves following cadmium treatment. However, the amount of photosystem II reaction center proteins and that of its light harvesting complex is not affected, indicating that cadmium does not adversely influence the structural organization of this photosystem. In thylakoids isolated from cadmium-treated plants a loss in the capability to reduce 2,6-dichlorophenolindophenol is observed, which is partially restored if diphenylcarbazide is used as an electron donor, indicating that cadmium affects water splitting activity. In thylakoids isolated from control plants and treated with cadmium, diphenylcarbazide preserves most of the photosystem II activity lost after incubation with cadmium; most of the S(2) multiline electron paramagnetic resonance signal from the manganese cluster is lost, whereas the TyrD(+) and other signals are retained. Light-induced photosystem II damage, in vitro, is promoted by Cd-treatment as deduced from the mobility shift of the D1 protein observed by immunoblot. 相似文献
70.
Summary. We propose and analyze a finite difference scheme for the Kohn Laplacian operator associated with the Heisenberg group, which
is a degenerate elliptic operator of H?rmander type. We give a complete analysis for a periodic problem in a cube. In particular,
we prove a discrete Poincaré-Wiertinger inequality which yields the stability. Numerical tests are presented.
Received June 1, 1999 / Revised version received June 7, 2000 / Published online March 20, 2001 相似文献