Propylene bulk phase oligomerization with bisiminepyridine iron catalysts: Mechanistic investigation of 1,2-versus 2,1-propylene insertion

Iron(II) complexes were synthesized with bisiminepyridine ligands of different steric demand. Activation with modified MAO (25 mol% isobutyl groups) generated very active catalysts for propylene oligomerization. These oligomerizations were carried out in liquid propylene in a heat flow calorimeter. The oligomers were separated by preparative gas chromatography and the dimers and trimers analyzed using analytical gas chromatography, ¹H-NMR-, and ¹³C NMR-spectroskopy. By means of the knowledge of the dimer and trimer structure, we were able to establish a mechanistic pathway for propylene insertion and obtained knowledge about the iron alkyl species involved. Analysis of the various dimers formed allowed us to determine the percentage of 1,2-versus 2,1-propylene insertions. Considering the same iron alkyl species with ligands of different steric demand, a change in the probabilities for 1,2-versus 2,1-propylene insertions can be observed. With this knowledge, the catalyst behaviour for ligands of varying steric demand can be predicted. The question of how to produce oligomers versus polymers is one of knowing how to control the ratio of the 1.2-and 2.1-insertion. One method is to alter the steric demand in the ortho position of the ligand. The more bulky the ligand, the more often a 2,1-propylene insertion happens and, therefore, the higher the molecular mass of the oligomers, i.e., polymer is formed. Another important observation is that the formation of α-olefines is favored with a higher steric demand of the catalyst. The text was submitted by the authors in English.     

Hyperfine Field in Ferromagnetic CoPd Alloys

The magnetic hyperfine interaction of ⁶⁰Co in the completely miscible alloy Co _x Pd_1−x was investigated for different values of x by measuring the nuclear orientation of ⁶⁰Co as function of temperature and by nuclear magnetic resonance of the oriented ⁶⁰Co nuclei. A broad resonance signal of Gaussian shape could be observed down to x=60%. The dependence of the mean magnetic hyperfine field on the Co concentration was observed to be linear very similar to that of experimental values of the magnetic moment per atom in the literature. The magnetic hyperfine field and its broad distribution are discussed in a simple model with RKKY interaction. This revised version was published online in September 2006 with corrections to the Cover Date.     

Services for replica consistency handling in data grids

The grid technology is a popular framework for collaborative, resource sharing computing infrastructure for many scientific domains. As wider scientific communities engage in the use of the grids, the view on the grid technology changes from the traditional high-performance computing perspective to a wider context. Data management is becoming one of the main areas of research interest in the scope of grid systems. In this paper, we present services for replica update propagation and consistency handling, which try to address the absence of software tools for maintaining the consistency among distributed data resources in a grid environment. We describe the architecture of the services as well as several important implementation details. We discuss the possibility of integration consistency handling services with legacy software and grid middleware services. This gives us the possibility to benefit from legacy software functionality and, in the same time, to increase the data availability and fault-tolerance by means of data replication. The text was submitted by the authors in English.     

Propylene bulk phase oligomerization with bisiminepyridine iron complexes in a calorimeter: mechanistic investigation of 1,2 versus 2,1 propylene insertion

Iron(II) complexes were synthesized with bisiminepyridine ligands of low steric demand. Activation with modified-methylaluminoxane (25 mol.% isobutyl groups) generated very active catalysts for propylene oligomerization. The oligomerizations were carried out in liquid propylene in a heat flow calorimeter. The oligomers were separated by preparative gas chromatography and the dimers and trimers analyzed using analytical gas chromatography, ¹H-NMR- and ¹³C-NMR-spectroscopy. With knowledge of the dimer and trimer structure, we were able to establish a mechanistic pathway for propylene insertion and obtained knowledge about the iron alkyl species involved. Analysis of the various dimers formed allowed us to determine the percentage of 1,2 versus 2,1 propylene insertions. Considering the same iron alkyl species with ligands of different steric demand, a change in the probabilities for 1,2 versus 2,1 propylene insertions can be observed. With this knowledge, the catalyst behavior for ligands of varying steric demand can be predicted.     

Effektive Synthese von 3,1′-Spiro[3,4-dihydro-2H-[1,3]oxazino[3,2-a]benzimidazol] cyclo- bzw. benzocycloalkanen sowie ihrer Thia-Analogen Über Spirane, 23. Mitt.

Ten new constitutionally unsymmetrical azaspiran systems were synthesized upon condensation of Na-derivatives of 2,3-dihydro-1H-benzimidazol-2-one and 2,3-dihydro-1H-benzimidazol-2-thione, respectively, with 1,1-bis(bromomethyl)-and 1,1-bis(iodomethyl)- and ditosylate of 1,1-bis(hydroxymethyl) cycloalkanes.

Vorgetragen auf dem 28. IUPAC-Kongreß in Vancouver (August 1981).     

An L2‐stable approximation of the Navier–Stokes convection operator for low‐order non‐conforming finite elements

We develop in this paper a discretization for the convection term in variable density unstationary Navier–Stokes equations, which applies to low‐order non‐conforming finite element approximations (the so‐called Crouzeix–Raviart or Rannacher–Turek elements). This discretization is built by a finite volume technique based on a dual mesh. It is shown to enjoy an L² stability property, which may be seen as a discrete counterpart of the kinetic energy conservation identity. In addition, numerical experiments confirm the robustness and the accuracy of this approximation; in particular, in L² norm, second‐order space convergence for the velocity and first‐order space convergence for the pressure are observed. Copyright © 2010 John Wiley & Sons, Ltd.     

A formally second‐order cell centred scheme for convection–diffusion equations on general grids

We propose, in this paper, a finite volume scheme to compute the solution of the convection–diffusion equation on unstructured and possibly non‐conforming grids. The diffusive fluxes are approximated using the recently published SUSHI scheme in its cell centred version, that reaches a second‐order spatial convergence rate for the Laplace equation on any unstructured two‐dimensional/three‐dimensional grids. As in the MUSCL method, the numerical convective fluxes are built with a prediction‐limitation process, which ensures that the discrete maximum principle is satisfied for pure convection problems. The limitation does not involve any geometrical reconstruction, thus allowing the use of completely general grids, in any space dimension. Copyright © 2012 John Wiley & Sons, Ltd.     

Gas density sensor for real-time monitoring in a high pressure reactor

We present the design of a gas density sensor based on quartz crystal resonators for high pressure (2.5 × 10⁶ Pa) and high temperature (340 K) application. Tunning fork resonators have successfully been used in gas density measurements. In our contribution tuning fork and thickness-shear mode devices are compared with respect to their sensitivity to gas density. It was confirmed, that tuning fork resonators are mainly sensitive to density, whereas shear-mode resonators aremore suitable for viscosity measurement. In high pressure gases, an additional pressure dependent frequently shift has to be considered.