Template-Directed Synthesis of Macroheterocycles by Ring-Closing Metathesis of Olefin-Substituted Pyridines in the Coordination Sphere of a Triplatinum Complex

Mono- and tris-3,5- and 2,6-pyridinediyl-containing macroheterocycles were synthesized by metathesis of olefin-substituted pyridines in the coordination sphere of mono- and tris-platinum complexes, respectively. Tris(2,6-pyridinediyl)-containing macroheterocycles were hydrogenated over palladium catalyst. The hydrogenated macrocycle was used as ligand for the triplatinum template. The structure of the resulting complex was established by X-ray analysis.     

Trimetallic FePd2 and FePt2 4-ferrocenyl-NCN pincer complexes

Ferrocene-bridged NCN pincer complexes of structural type Fe(η⁵-C₅H₄-4-NCN-1-MX)₂ (X = I: 6, M = Pd; 7, M = Pt; X = Cl: 8, M = Pt; NCN = [4-C₆H₂(CH₂NMe₂)₂-2,6]⁻) are accessible by the subsequent reaction of Fe(η⁵-C₅H₄-4-NCNH)₂ (4) with ⁿBuLi and [PtCl₂(SEt₂)₂] (synthesis of 8) or treatment of Fe(η⁵-C₅H₄-4-NCN-1-I)₂ (5) with [Pd₂(dba)₃] (synthesis of 6) or [Pt(tol)₂(SEt₂)]₂ (synthesis of 7) (dba = dibenzylidene acetone, tol = 4-tolyl). In addition, the Sonogashira cross-coupling of Fe(η⁵-C₅H₄I)₂ (1) with HCC-4-NCNH (2) gives Fe(η⁵-C₅H₄-CC-4-NCNH)₂ (3). The reaction behavior of 3 towards ^tBuLi is reported as well.Cyclovoltammetric studies show that the ferrocene entity can be oxidized reversibly. The Fe(II)/Fe(III) potential decreases with increasing electron density at the NCN pincer units due to the presence of the M-halide moiety (M = Pd, Pt).The solid state structure of Fe(η⁵-C₅H₄-4-NCN-1-PdI)₂ (6) is presented. In 6 the Fe(η⁵-C₅H₄)₂ unit connects two NCN-PdI pincer entities with palladium in a square-planar environment. The cyclopentadienyl ligands show a staggered conformation. The C₆H₂ rings are tilted by 23.5(3)° towards the C₅H₄ entities and the C₆H₂ plane is almost coplanar with the coordination plane (10.3(3)°).     

Canonical variables for crossing multiparticle amplitudes

Canonical variables for arbitrary multiparticle amplitudes are defined which have the property that under crossing all variables except two energies stay in their physical domain.     

Aminoarenethiolate-copper(I)-catalyzed amination of aryl bromides

[reaction, structure: see text] Aminoarenethiolate-copper(I) complexes are known to be efficient catalysts for carbon-carbon bond formation. Here, we show the first examples that these thiolate-copper(I) complexes are efficient for carbon-nitrogen bond formation reactions as well. N-Arylation of benzylamine and imidazole with bromobenzene was achieved either in NMP as solvent or under solvent-free conditions in the presence of 2.5 mol % of aminoarenethiolate-copper(I) complex only.     

Covariant electroweak nucleon form factors in a chiral constituent-quark model

Results for the proton and neutron electric and magnetic form factors as well as the nucleon axial and induced pseudoscalar form factors are presented for the chiral constituent-quark model based on Goldstone-boson exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The direct predictions of the model yield a remarkably consistent picture of the electroweak nucleon structure. Received: 28 February 2002 / Accepted: 14 March 2002     

Untersuchung der Photochemie von Polyenen mit Hilfe von mikroprozessor-gesteuerter HPLC

Ohne Zusammenfassung

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Photochemical examination of polyenes by microprocessor controlled HPLC

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Wir danken Frau Prof. Breyer-Pfaff für die Moglichkeit, im Institut für Toxikologie Densitogramme aufnehmen zu konnen, und der Deutschen Forschungsgemeinschaft für personelle und finanzielle Unterstiitzung.     

Electric field dependence of the dielectric susceptibility in K1−xLixTaO3

Results are presented for the dielectric function $\text{ε1 = ε}{}_1\text{+ iε}{}_2$ in K_1?xLi_xTaO₃ in the frequency range 10 < f < 10⁶ Hz and for several fields. The data are analysed in terms of dielectric relaxation, and it is shown that the electric bias field modifies the relaxation behaviour drastically.     

Nuclear magnetic relaxation of 23Na in polyelectrolytes with mono/divalent ion clouds

The nuclear magnetic relaxation rate of ²³Na ions in polyelectrolyte solutions containing both monovalent and divalent counter-ions is investigated to obtain information on the nature of the divalent ion/poly-ion interaction.