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51.
The reduction of Pt(IV) complexes followed by the oxidative addition of dimethyl sulfate to Pt(II) affords Cs2PtMe2Cl4, a complex of dimethylplatinum(IV). On treatment with such nucleophiles as Cl–, Br–, I–, and PtCl4
2– in aqueous solutions at 368 K this complex undergoes reductive elimination to give MeX and PtIIMe as a transient species. The latter is further converted to methane upon protolysis, whereas in the presence of an oxidant (Na2PtCl6) it gives rise to the PtIVMe species. The kinetics of decomposition of Cs2PtMe2Cl4 in aqueous HCl-KCl systems (2M or 3M in Cl–; [PtIVMe2][Cl–]) were studied. The reaction takes place as anS
N
2 attack of X– on the carbon atom of a methyl group located with thetrans position with respect to the aqua-ligand of the [PtMe2Cl3(H2O)]– complex.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 389–395, February, 1993. 相似文献
52.
Reaction of trans-[Pt(H)2(PCy3)2], 1, with [60]fullerene at room temperature affords [Pt(PCy3)2(η2-C60)], 2, in nearly quantitative yield. The most probable reaction pattern is the insertion of a fullerene 6,6 junction onto a Pt-H bond yielding an η1 alkyl derivative which, after hydrogen extrusion, gives 2. On the other hand, addition of 1 to different electron-deficient olefins, such as dimethyl maleate and fumarate, furnishes mixtures of both η1 metal—alkyl and η2 metal—olefin derivatives. If tetrachloroethylene is used as 2π component, trans-[PtCl(H)(PCy3)2] forms exclusively. 相似文献
53.
54.
Cristina Tealdi Lorenzo Malavasi Giorgio Flor 《Journal of solid state chemistry》2004,177(11):4359-4367
Atomistic computer simulation techniques have been used, for the first time, to reproduce the crystal structure of MgTa2O6 and to investigate the defect chemistry and dopant properties of this material. The calculated defect energetics suggest that the concentration of intrinsic atomic defects in this phase is insignificant and that the system is probably stable to both oxidation and reduction. Dopant solution energy versus ion size trends are found for both isovalent and aliovalent dopant incorporation at Mg and Ta sites. Divalent dopants (e.g. Ca, Cu) preferentially occupy the Mg site whereas dopants with higher charge (e.g. Sc, Zr, Nb) are more favorable on the Ta site. High migration activation energies (>2 eV) predict limited ionic conductivity in this material. 相似文献
55.
Nucleophilic vinylic substitutions of 4H-pyran-4-one and 2-methyl-4H-pyran-4-one with ammonia were calculated by the B3LYP method using the 6-31G(d,p) basis set. Bulk solvent effects of aqueous
solution were estimated by the polarized continuum and Poisson–Boltzmann self-consistent reaction field models using the 6-311+G(d,p)
basis set. In the gas phase different mechanisms were found for the two reaction systems calculated. The reaction of 4H-pyran-4-one proceeds through enol, whereas a feasible path for the less reactive 2-methyl-4H-pyran-4-one is the mechanism through a keto intermediate. Addition of ammonia in concert with proton transfer is the rate-determining
step ofthe reaction. The mechanism proceeding either by a bimolecular nucleophilic substitution (SN2) or by one involving a tetrahedral zwitterionic intermediate is shown to be unlikely in the gas phase or nonpolar solution.
The effects of bulk solvent not only consist in a reduction of the various activation barriers by about 25–40 kJ mol−1 but also in a change in the reaction mechanism.
Received 26 May 2002 / Accepted 26 July 2002 /
Published online: 14 February 2003 相似文献
56.
Defect turbulence described by the one-dimensional complex Ginzburg–Landau equation is investigated and analyzed via a birth–death process of the local structures composed of defects, holes, and modulated amplitude waves (MAWs). All the number statistics of each local structure, in its stationary state, are subjected to Poisson statistics. In addition, the probability density functions of interarrival times of defects, lifetimes of holes, and MAWs show the existence of long-memory and some characteristic time scales caused by zigzag motions of oscillating traveling holes. The corresponding stochastic process for these observations is fully described by a non-Markovian master equation. 相似文献
57.
58.
Polystyrene-supported 2-azidoethyl phenyl selenide and 3-azidopropyl phenyl selenide reagents have been developed and applied to the traceless solid-phase organic synthesis of 1-vinyl- and 1-allyl-1,2,3-triazoles by CuI-mediated azide–alkyne cycloadditions and subsequent cleavage from the polymer support through oxidation–elimination reaction with 30% hydrogen peroxide. The advantages of this method include straightforward operation, good yield and purity of the products, and good stability and lack of odor for the reagents. 相似文献
59.
Angelo Ranise Francesco LucchesiniMatteo Caviglia Silvana AlfeiAndrea Spallarossa Chiara Caneva 《Tetrahedron》2013
A simple one-pot procedure for the stereoselective synthesis of Knoevenagel-type indoles is described. The method is based on the in situ reaction of indole iminium salts (four of them are fully characterized) with acyclic symmetrical and unsymmetrical active methylene reagents in the presence of triethylamine. In general, the overall yields are moderate to good. Some of relevant reaction parameters and steric effects affecting stereoselectivity are discussed. 相似文献
60.
Exploring Regioselective Bond Cleavage and Cross‐Coupling Reactions using a Low‐Valent Nickel Complex
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Addison N. Desnoyer Florian W. Friese Weiling Chiu Marcus W. Drover Dr. Brian O. Patrick Prof. Dr. Jennifer A. Love 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):4070-4077
Recently, esters have received much attention as transmetalation partners for cross‐coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}2(μ‐η2:η2‐C6H6)] (dtbpe=1,2‐bis(di‐tert‐butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η2‐carbonyl complexes. In contrast, acetylthioesters underwent rapid Cacyl?S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross‐coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η2‐carbonyl complex, phenyl esters were found to predominantly undergo Caryl?O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2‐naphthyl acetate was also found to undergo clean Caryl?O bond cleavage, and although stoichiometric cross‐coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive. 相似文献