Ruthenium-catalysed linear-selective allylic alkylation of allyl acetates

The regioselectivity in the ruthenium-catalysed allylic alkylation of mono substituted allyl acetates with the malonate anion was highly controlled by Ru3(CO)12 with 2-(diphenylphosphino)benzoic acid, and the linear-type alkylated product was obtained.     

Isotactic poly(butene‐1) trigonal crystal growth in the melt

Crystal growth of the trigonal form of isotactic poly(butene‐1) (it‐PB1) was successfully observed in the melt at atmospheric pressure. The growth rate of trigonal crystals was obtained by in situ optical microscopy. It is one hundredth that of it‐PB1 tetragonal crystals. The growth rate of trigonal crystals, as well as that of tetragonal crystals, shows supercooling dependence derived from the nucleation theory. The value of the kinetic constant K of trigonal crystals is about 3.3 times larger than that of tetragonal crystals. The value of the pre‐exponential factor G₀ of trigonal crystals was found to be 41 times as large as that of tetragonal crystals. The difference between these K values can be attributed to the conformational entropy of the ethyl side groups in a nucleating stem. The discrepancy found in the values of G₀ could be explained by introducing pinning and nucleation barriers, which originate from the crystal thickness δl_c, which does not depend on the crystallization temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 684–697, 2007     

New critical point induced by the axial anomaly in dense QCD

We study the interplay between chiral and diquark condensates within the framework of the Ginzburg-Landau free energy, and classify possible phase structures of two and three-flavor massless QCD. The QCD axial anomaly acts as an external field applied to the chiral condensate in a color superconductor and leads to a crossover between the broken chiral symmetry and the color superconducting phase, and, in particular, to a new critical point in the QCD phase diagram.     

Raising sfermion masses by adding extra matter fields

The renormalization group flow of soft supersymmetry breaking masses is sensitive to the field contents of the theory one considers. We point out that the addition of extra vector-like matter fields to the minimal supersymmetric standard model raises the masses of squarks and sleptons relative to those of gauginos. We discuss its phenomenological implications. Besides an obvious effect to the superparticle mass spectrum, we find that radiative corrections from heavier stop loops increase the lightest CP-even Higgs boson mass. We also discuss impact on models with no-scale boundary conditions. It turns out that, unlike the minimal case, staus can become heavier than a B-ino like neutralino, which is cosmologically favored.     

A general nickel-catalyzed hydroamination of 1,3-dienes by alkylamines: catalyst selection, scope, and mechanism

A simple colorimetric assay of various transition-metal catalysts showed that the combination of DPPF, Ni(COD)(2), and acid is a highly active catalyst system for the hydroamination of dienes by alkylamines to form allylic amines. The scope of the reaction is broad; various primary and secondary alkylamines react with 1,3-dienes in the presence of these catalysts. Detailed mechanistic studies revealed the individual steps involved in the catalytic process. These studies uncovered unexpected thermodynamics for the addition of amines to pi-allyl nickel complexes: instead of the thermodynamics favoring the reaction of a nickel allyl with an amine to form an allylic amine, the thermodynamics favored reaction of a nickel(0) complex with allylic amine in the presence of acid to form a Ni(II) allyl. The realization of these thermodynamics led us to the discovery that nickel and some palladium complexes in the presence or absence of acid catalyze the exchange of the amino groups of allylic amines with free amines. This exchange process was used to reveal the relative thermodynamic stabilities of various allylic amines. In addition, this exchange reaction leads to racemization of allylic amines. Therefore, the relative rate for C-N bond formation and cleavage influences the enantioselectivity of diene hydroaminations.     

Enantioselective C-S bond formation by iron/Pybox catalyzed Michael addition of thiols to (E)-3-crotonoyloxazolidin-2-one

The enantioselective Michael addition of thiols to (E)-3-crotonoyloxazolidin-2-one was effectively catalyzed by the Fe(BF₄)₂·6H₂O/(S,S)-ip-Pybox catalyst, and the addition product was obtained with up to a 95% ee.     

Studies of the state of iron contained in α- and β-silicon nitride by Mössbauer and Raman effects

The Mössbauer spectra of β- and α-Si₃N₄ containing Fe have been measured at 300 and 93 K. The former consists of a singlet and a doublet, whereas the latter exhibits paramagnetic hyperfine patterns and a doublet. The single line and hyperfine patterns arise from isolated high-spin Fe³⁺ ions which are bonded equivalently with 4 nitrogen neighbors. Both doublets arise from high-spin Fe³⁺ ion-pairs each of which is strongly bonded by a kind of superexchange force. In β-Si₃N₄ the Fe³⁺ ions occupy the same sites regardless of whether they are doped into the crystal lattice before or after its preparation, while in α-Si₃N₄ the Fe³⁺ ions are located at different sites depending on the doping procedure. From the Raman spectra, the difference in the Mössbauer spectra for the two compounds is attributable to different relaxation by lattice phonons of the host crystals.The Mössbauer spectral lines for β-Si₃N₄ alone have been found to decrease in intensity with tune even at room temperature, such an ageing being observed to be entirely suppressed by γ-irradiation. From different behaviors of the three lines in the ageing and quenching from 1150°C down to room temperature, the ageing is interpretable based on a model that the Fe³⁺ ions jump from substitutional sites into interestitial sites and take place thermal vibration with a large amplitude there.