Polymer-supported bisBINOL ligands for the immobilization of multicomponent asymmetric catalysts

[reaction: see text] Polymer-supported bisBINOL ligands were successfully utilized for the immobilization of multicomponent asymmetric catalysts. The polymer-supported Al-Li-bis(binaphthoxide) (ALB) catalyst was more effective than the dendrimer-supported ALB in the Michael reaction of 2-cyclohexen-1-one with dibenzyl malonate affording the adduct in 91% yield with 96% ee. The polymer was also effective for the immobilization of a mu-oxodititanium complex that promoted carbonyl-ene reaction of ethyl glyoxalate with alpha-methyl styrene to provide the adduct with up to 98% ee.     

DFT Study of a 5‐endo‐trig‐Type Cyclization of 3‐Alkenoic Acids by Using Pd–Spiro‐bis(isoxazoline) as Catalyst: Importance of the Rigid Spiro Framework for Both Selectivity and Reactivity

The reaction pathway of an enantioselective 5‐endo‐trig‐type cyclization of 3‐alkenoic acids catalyzed by a chiral palladium–spiro‐bis(isoxazoline) complex, Pd–SPRIX, has been studied by density functional theory calculations. The most plausible pathway involves intramolecular nucleophilic attack of the carboxylate moiety on the C?C double bond activated by Pd–SPRIX and β‐H elimination from the resulting organopalladium intermediate. The enantioselectivity was determined in the cyclization step through the formation of a π‐olefin complex, in which one of the two enantiofaces of the olefin moiety was selected. The β‐H elimination occurs via a seven‐membered cyclic structure in which the acetate ligand plays a key role in lowering the activation barrier of the transition state. In the elimination step, the SPRIX ligand was found to behave as a monodentate ligand due to the hemilability of one of the isoxazoline units thereby facilitating the elimination. Natural population analysis of this pathway showed that the more weakly electron‐donating SPRIX ligand, compared with the bis(oxazoline) ligand, BOX, facilitated the formation of the π‐olefin complex intermediate, leading to a smaller overall activation energy and a higher reactivity of the Pd–SPRIX catalyst.     

PVTx relationships and solid-liquid equilibria for the m-xylene-p-xylene system under high pressures

PVTx relationships of the m-xylene-p-xylene system have been measured with a glass piezometer at 283.15 and 298.15 K and pressures up to 200 MPa, or up to the point of solidification of m-xylene where this occurred at a lower pressure. Freezing pressures of m-xylene were observed as a discontinuity in the volume at increasing pressure. Approximate solid-liquid equilibria under high pressures were obtained from the freezing pressure measurement. The Carnahan-Starling-van der Waals (CS-vdW) equation of state was used to correlate the PVTx data. The solid-liquid equilibria under high pressures were calculated with the CS-vdW equation of state for the liquid phase and a simple equation of state for the solid phase. In order to test the validity of the calculation method, the solid-liquid equilibrium relationships of the benzene-cyclohexane system were also calculated. It was found that the solid molar volume should be treated as a function of temperature and/or pressure to fit the experimental data.     

The role of a radial ion-track distribution in semiconductors studied by numerical simulations

The effect of radial ion-track distribution on the transient current in semiconductors caused by a high-energy heavy ion strike was studied. Reasonable agreement was observed in experimental and calculated transient currents for ion energies ranging from several to several hundred MeV when the radius of the ion track used in the numerical simulations was shorter or equivalent to that of the penumbra radius.     

Discontinuous boundary implementation for the shallow water equations

Quasi‐bubble finite element approximations to the shallow water equations are investigated focusing on implementations of the surface elevation boundary condition. We first demonstrate by numerical results that the conventional implementation of the boundary condition degrades the accuracy of the velocity solution. It is also shown that the degraded velocity leads to a critical instability if the advection term is present in the momentum equation. Then we propose an alternative implementation for the boundary condition. We refer to this alternative implementation as a discontinuous boundary (DB) implementation because it introduces at each boundary node two independent mass–flux values that result in a discontinuity at the boundary. Numerical results show that the proposed DB implementation is consistent, stabilizes the quasi‐bubble scheme, and leads to second‐order accuracy at the surface elevation specified boundary. Copyright © 2004 John Wiley & Sons, Ltd.     

Molecular distortion effect on ff-emission in a Pr(III) complex with 4,7-diphenyl-1,10-phenanthroline.

The electronic and structural behaviour of a Pr(III) complex with 4,7-diphenyl-1,10-phenanthroline, [Pr(bathophen)(2)(NO(3))(3)], is investigated with respect to the effect of configuration changes on the Pr(III) centre. [Pr(bathophen)(2)(NO(3))(3)] luminesces from the excited states of the ligand and the metal ion. The fluorescence, ff-emission ((1)D(2)-->(3)H(4)), and phosphorescence bands appear at 394, 608.2 and 482 nm, respectively, in the solid state. In acetonitrile, the complex also shows multiple emissions. From the time-resolved emission and the lifetime measurements, the excitation energy-transfer in [Pr(bathophen)(2)(NO(3))(3)] is clarified, that is, the upper excited triplet level of the ligand acts as an energy donor, while the (1)D(2) levels of Pr(III) is the acceptor. Additionally, the emission phenomena of the complex can be modified by molecular distortion, particularly by rotation of the phenyl groups in the ligand.     

Binary nucleation rates for ethanol/water mixtures in supersonic Laval nozzles

Although the conditions corresponding to the onset of condensation of aqueous-alcohol mixtures have been measured in supersonic nozzles [B. E. Wyslouzil et al., J. Chem. Phys. 113, 7317 (2000)], the true nucleation rates have not. Here, we propose a new analytical method to estimate the temperature, the concentrations of condensable species in both the vapor and the liquid phases, and the amount of the condensate using only the measured static pressure profiles in the nozzle. We applied the method to ethanol/water (CH(3)CH(2)OH/D(2)O or CH(3)CH(2)OD/D(2)O) mixtures and confirmed that the aerosol volume fractions derived from pressure measurements and small angle neutron scattering measurements are in very good agreement when this method is used. Combining the results from the pressure measurements with the number densities of the condensed droplets, measured either by small angle neutron or small angle x-ray scattering, we determined the first quantitative ethanol/water binary nucleation rates in the supersonic nozzle at a temperature of 229±1?K.     

Initial step of anthracene‐sensitized photoacid generation from diphenyliodonium hexafluorophosphate in an epoxy matrix studied by steady‐state and laser‐flash photolyses

The anthracene‐sensitized photodecomposition of diphenyliodonium hexafluorophosphate was studied in an epoxy matrix. From steady‐state photolysis, the generation of protons, which are considered to be the actual initiators of the polymerization of epoxides, was confirmed. In addition, 9‐phenylanthracene was detected as a main product from anthracene. From time‐resolved laser‐flash photolysis, a broad absorption band with a peak at about 500 nm was observed that was thought to be due to the precursor of 9‐phenylanthracene. On the basis of these results, we propose electron transfer from anthracene in the excited singlet state to the diphenyliodonium cation as the initial step of photoacid generation. This process is followed by fast chemical reactions, which generate 9‐phenylanthracene and protons, and back electron transfer from the diphenyliodine radical to the anthracene cation radical. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2937–2946, 2001