Conceptually new chiral tertiary C2 symmetric diamines in asymmetric synthesis

New chiral diamines were prepared, based on the cyclohexane diamine core. The two different substituents on each nitrogen allow this heteroatom to become a stereogenic center upon chelation with a metal, such as lithium. The enantioselective addition of MeLi to imines, with ee's up to 68%, illustrates the validity of this concept.     

Bis(1-methylbenzotriazole)dinitratocobalt(II): A pseudo-octahedral complex with pseudo-tetrahedral magnetochemical and ligand field characteristics

Summary The reaction between cobalt(II) nitrate and 1-methylbenzotriazole (MeBTA) leads to a complex with unusual magnetochemical and ligand field characteristics. The synthesis and the physical and spectroscopic properties of the pseudo-octahedral complex [Co(MeBTA)₂(NO₃)₂] are described.

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Bis(1-methylbenzotriazol)dinitratocobalt(II): Ein pseudo-octaedrischer Komplex mit pseudotetraedrischen magnetochemischen und Ligandenfeld-Charakteristika (Kurze Mitt.)

Zusammenfassung Die Reaktion zwischen Kobalt(II)nitrat und 1-Methylbenzotriazol (MeBTA) führt zu einem Komplex mit ungewöhnlichen magnetochemischen und Ligandenfeld-Eigenschaften. Die Synthese und die spektroskopischen Eigenschaften des pseudo-octaedrischen Komplexes [Co(MeBTA)₂(NO₃)₂] werden beschrieben.

     

Measurement of quadratic electrooptic coefficients in LiNbO3 using a variation of the FDEOM method

Calculations on the optical index ellipsoid yield that in LiNbO₃, a quadratic electrooptic effect free of its linear counterpart exists only for propagation along the X-crystal axis with a longitudinal electric field and in that case the quadratic coefficients R _c =R ₁₂–R ₃₁ and R ₄₁ are exclusively involved. Because of their low values, we have measured these coefficients using a specific novel variation of the accurate frequency-doubling electrooptic modulation (FDEOM) method. After a presentation of the theoretical formulation and practical implementation of this method, results for R _c and R ₄₁ are given and discussed in relation to theoretically expected values.     

Pulse propagation in a nonlinear dielectric slab waveguide

The evolution of an optical pulse in a single-mode, step index dielectric slab waveguide which is characterized by an intensity dependent dielectric function in the core and cladding regions is treated by means of differential equation techniques. A cubic order non-linearity is considered. The electromagnetic field distribution in the slab waveguide region satisfies a non-linear wave equation. This field can be represented in terms of even TE guided modes with a slowly varying envelope amplitude function.Then using the well known approximation, based on the slowly varying character of the amplitude function, a non linear partial differential equation is obtained for the amplitude function. As the coefficients of this equation depend on the distance across the transverse direction X, an averaging technique over x is applied to reduce the nonlinear partial differential equation into a form that is easily transformed to the so-called non-linear Scroedinger differential equation.This equation is then attacked by means of the well known Inverse Scattering method in the case of reflection less potentials. The single and double soliton solutions are obtained explicitly for a single-mode slab waveguide. Finally numerical results are presented in the time domain.     

Quasi-periodicity,global stability and scaling in a model of Hamiltonian round-off

We investigate the effects of round-off errors on the orbits of a linear symplectic map of the plane, with rational rotation number nu=p/q. Uniform discretization transforms this map into a permutation of the integer lattice Z(2). We study in detail the case q=5, exploiting the correspondence between Z and a suitable domain of algebraic integers. We completely classify the orbits, proving that all of them are periodic. Using higher-dimensional embedding, we establish the quasi-periodicity of the phase portrait. We show that the model exhibits asymptotic scaling of the periodic orbits and a long-range clustering property similar to that found in repetitive tilings of the plane. (c) 1997 American Institute of Physics.     

Reactivity of RCu,BF3 and R2 CuLi,BF3 towards allylic acetals and ethers

Organocopper and cuprate reagents associated with Lewis acids, are highly reactive towards allylic acetals and ethers. Displacements of the alkoxy group occurs by SN₂' attack according to the various parameters of the reaction.     

Complexes of divalent transition metal chlorides with the tetradentate Schiff base ligand 1,2-bis(2′-pyridylmethyleneimino)-benzene

Summary Transition metal(II) chloro complexes of the new Schiff base ligand 1,2-bis(2-pyridylmethyleneimino)benzene (L), derived from 2-pyridinecarboxaldehyde and 1,2-phenylenediamine, were prepared. Compounds of [MnLCl₂]-H₂O, [CoLCl₂]·2H₂O, [NiLCl₂] and [Zn₃L₂Cl₄]Cl₂ were prepared. Details are given of the formation of the complex [Cu(L·EtOH)Cl₂], in which one molecule of EtOH adds across only one of the Schiff base {ie531-01} groups to give the coordinated ligand L·EtOH. The rationalization of this type of reaction by considering the steric requirements of the ligand is given. The complexes were characterized by elemental analyses, conductivity measurements, thermal techniques, mass spectra, magnetic susceptibilities and spectroscopic (i.r., ligand field, e.s.r., ¹H n.m.r.) studies. The nitrogen donor atoms of the tetradentate ligands L and L·EtOH are assumed to adopt an essentially planar arrangement about manganese(II), cobalt(II), nickel(II) and copper(II), with the remaining axial coordination sites occupied by chloro ligands to yield high-spin octahedral molecules. A trinuclear structure, based on tetrahedrally coordinated metal ions, is proposed for the zinc(II) complex.     

Reactions of 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) with yttrium(III) nitrate: preparation,X-ray crystal structures and spectroscopic characterization of the bis-bpy and bis-phen complexes

Y(NO₃)₃ · 5H₂O reacts with 2,2-bipyridine (bpy) and 1,10-phenanthroline (phen) to yield similar complexes of 1:2 yttrium:ligand stoichiometry. The crystal structures of the two complexes, namely, [Y(NO₃)₃(bpy)₂] (1) and [Y(NO₃)₃(phen)₂] (2), are reported. The three nitrate groups are O,O-bidentate and the organic ligands are also bidentate. In both structures the metal ion lies on a crystallographic two-fold axis. The stereochemistry about Y^III can be viewed as a sphenocorona. The new complexes were characterized by elemental analyses and spectroscopic (i.r., ¹H-n.m.r. and ¹³C-n.m.r.) techniques. The data are discussed in terms of the nature of bonding and known solid state structures.