Jürgen Buschmann

Experimental electron density study of ethylene oxide at 100 K.

The experimental electron density of ethylene oxide was derived from a multipole refinement of 100 K X-ray data and complemented by density-functional calculations at experimental and optimized geometry. Atomic and bond-topological properties were derived using the atoms-in-molecules (AIM) formalism. The high strain in the three-membered ring molecule is mainly expressed by the high ellipticities of the three bonds in this ring, while the bond paths are only slightly bent for the C-C bond, but are virtually straight for the C-O bond.

Synthesis of optically active 1-t-butyl-4-ethylidenecyclohexane via CO2-elimination from a spirofused β-lactone

(R)-l-t-Bulyl-4-ethylidene cyclohexane ((R)-1) is prepared with > 98% ee from 4-t-butylcyclo-hexane carhoxylic acid via the optically active β-lactone 10.

S4NR (R=Methyl, n‐Octyl) as Novel Chelating Ligands in Titanocene Complexes and First Synthesis of Small Sulfurimide Heterocycles SnNR (n=5, 6)

Not the expected insertion into a S-S bond but rather substitution of one NR unit takes place in the reaction of [Cp2 Ti(CO)2 ] with cyclic tetrasulfurdiimides 1,4-S4 (NR)2 . The product obtained contains the novel ligand S4 NR and serves as precursor in the synthesis of small SN heterocycles not accessible before (see below).

Eine neue Schwefelmodifikation: einfache Synthese von cyclo-S14 aus S8

Drei einfache Synthesestufen fuhren von S8 zu cyclo-S14, das bei 20°C bestandig ist. Der letzte Syntheseschritt [Gl. (a)] liefert die Titelverbindung, die spektroskopisch und rontgenographisch charakterisiert wurde. Formal entsteht die Struktur von S14 durch Einschieben einer S2-Einheit in S12. tmeda = N,N,N′,N′-Tetramethylethylendiamin.

Crystal and molecular structure of 1,2-difluoroethane and 1,2-diiodoethane

A single crystal of phase 1 of 1,2-difluoroethane was grown from the melt directly on an X-ray diffractometer close to the melting point of 169 K. It crystallizes in the monoclinic space group C2/c with lattice parameters a = 7.775(4), b = 4.4973(7), c = 9.024(3) Å, β = 101.73(1)°, V = 308.9(2) Å3, dcalc = 1.420 g cm−3 for Z = 4. A second phase of 1,2-difluoroethane was obtained under similar conditions which crystallizes in the orthorhombic space group P212121 with the unit cell parameters a = 8.0467(16), b = 4.5086(9), c = 8.279(2) Å,V = 300.36(11) Å3, dcalc = 1.461 g cm−3 for Z = 4. In both phases the 1,2-difluoroethane molecules adopt the gauche conformation with F–C–C–F torsion angles close to 68°. Crystals of 1,2-diiodoethane C2H4I2 were grown from pentane at −30°C. A platelet single crystal of the size 0.35 × 0.25 × 0.03 mm was measured with Mo Kα-radiation at 153 K. 1,2-Diiodoethane crystallizes in the monoclinic space group P21/n with a unit cell of a = 4.6051(7), b = 12.939(2), c = 4.7318(7) Å, β = 104.636(3)°, V = 272.79(7) Å3, Z = 2, dcalc = 3.431 g cm−3, μ(MoKα) = 11.353 mm−1. In the molecule the two neighboring iodine atoms are positioned anti. The shortest intermolecular contacts occur via iodine–iodine interactions resulting in layers of molecules in the crystal.

TOPOLOGICAL ANALYSIS OF THE EXPERIMENTAL ELECTRON DENSITY OF DIISOCYANOMETHANE AT 115 K

The electron density distribution of diisocyanomethane (see picture) is obtained from single-crystal X-ray diffraction data and by ab initio calculations. Multipole models with different restraints are applied to judge the physical significance of the parametrization of the experimental density. Topological indices as well as the electrostatic potential indicate crystal field effects.

Synthesis and structural studies of anomeric 2,3,4,6-tetra-O-acetyl-5-thio-D-glucopyranosyl azides

Abstract Two methods are presented for the preparation of the α and β anomers of 2,3,4,6-tetra-O-acetyl-5-thio- d -glucopyranosyl azide. These methods are comparable in yield, but the one that converts a glucopyranosyl bromide into the azide is preferable because of easier purification. After chromatographic separation, the α and β anomers were analysed by NMR spectroscopy. The crystal and molecular structure of the β anomer was determined by X-ray diffraction. It crystallises in space group P21 [a=11.729(3), b=7.305(3), c=11.363(3)A, β=107.63(5)°, Z=2]. The hexopyranose ring of the β anomer assumes a 4C1 conformation and the orientation of the azido group is compatible with the requirements of the exo-anomeric effect. This geometry is compared to that of other similar structures.

ANSA MACROLIDES AS MOLECULAR WORKBENCHES: STEREOCONTROLLED SYN ADDITIONS TO E OLEFINS

Fixed on an aromatic platform in a conformationally defined way, acyclic (E)-alkenes can be considered gripped on a molecular workbench. The olefinic ansa-macrolides formed in this way are shielded on one face. On epoxidation and dihydroxylation [Eq. (1)] the attack on the double bond takes place diastereoselectively from outside the ring, and the ansa chain can subsequently be cleaved from the workbench by mild hydrogenolysis. Bn=benzyl, NMO=N-methylmorpholin-N-oxide.

Low-temperature crystallization and X-ray structure determination of hexafluoropropene at 95 K

Crystals of hexafluoropropene, C3F6, melting point 115 K, were obtained by low temperature crystallization on the diffractometer in a cold N2 gas stream. The crystal structure was solved based on a dataset of 1347 reflections ((sinθ/λmax = 0.66 Å-1 ) measured at 95 K. C3F6 crystallizes in the triclinic space group P-1 (No. 2), a = 6.072(6) Å, b = 6.233(5) Å, c = 6.569(6) Å, α = 92.33(5)°, β = 108.75(7)°, γ = 94.31(5)°, V = 234.2(6) Å3, Z = 2, R1 = 0.050 for 729 reflections ( Fo2 > 2σ(Fo2)). The molecular structure has almost Cs symmetry with all atoms in a common plane except two fluorine atoms of the CF3 group. The fluorine atom of the CF3 group in the molecular plane is in trans position to the fluorine atom bonded to the central carbon atom. The geometrical parameters obtained from X-ray data are compared to those from an earlier gas phase electron diffraction study and, moreover, to those, obtained by theory from different high level ab initio calculations which were carried out as well for hexafluoropropene as for propene itself.

Synthese, Strukturuntersuchung und Koordinationschemie von Isocyanacetonitril

Isocyanacetonitril 1 wurde durch Ugi-Synthese ausgehend von Aminoacetonitril synthetisiert. Die Struktur und relative Energie von 1 wurde im Vergleich mit Malonodinitril und Diisocyanmethan mit ab initio Methoden MP2/6-31G** berechnet. 1 kristallisiert beim Abkuhlen unterhalb von –14 °C zu einem farblosen Feststoff, monoklin, Pn, a = 614.9(2), b = 756.3(1), c = 786.4(3) pm, β = 98.99(4)°, Z = 4, R1 = 0.054, wR2 = 0.132 mit zwei Molekulen in der asymmetrischen Einheit. Bei Raumtemperatur polymerisiert 1 zu einem braunen schwerloslichen Feststoff 2. Durch Koordination an Metallfragmente kann 1 deutlich stabilisiert werden. Die Metallkomplexe (CO)5M(CNCH2CN) (3) (a, M = Cr; b, M = W), CpMn(CO)2(CNCH2CN) (4) und fac-(CO)3W(CNCH2CN)3 (5) wurden synthetisiert und mit spektroskopischen Methoden charakterisiert. Die Strukturen von 3 a, monoklin, C2/c, a = 2481.4(7), b = 582.2(2), c = 2053.3(6) pm, β = 134.57(2)°, R1 = 0.0368, wR2 = 0.1001, und 4, monoklin, P21/a, a = 1223.7(2), b = 586.0(1), c = 1446.3(3) pm, β = 97.81(2)°, R1 = 0.0459, wR2 = 0.1190, wurden durch Rontgenbeugung an Einkristallen bestimmt. Synthesis, Structure, and Coordination Chemistry of Isocyanoacetonitrile Isocyanoacetonitrile 1 was synthesized starting from aminoacetonitrile by the Ugi method. The structure and relative energies of 1 were calculated by ab initio methods (MP2/6-31G**) in comparison with malonodinitrile and diisocyanomethane. 1 crystallizes on cooling below –14 °C forming a colourless solid, monoclinic, Pn, a = 614.9(2), b = 756.3(1), c = 786.4(3) pm, β = 98.99(4)°, Z = 4, R = 0.054, wR2 = 0.132, with two molecules representing the asymmetric unit. 1 polymerizes readily at ambient temperature forming a dark-brown almost insoluble solid 2. 1 can be stabilized by coordination to metal fragments. The metal complexes (CO)5M(CNCH2CN) (3) (a, M = Cr; b, M = W), CpMn(CO)2(CNCH2CN) (4) and fac-(CO)3W(CNCH2CN)3 (5) were synthesized and characterized by spectroscopic methods. The structures of 3 a, monoclinic, C2/c, a = 2481.4(7), b = 582.2(2), c = 2053.3(6) pm, β = 134.57(2)°, R1 = 0.0368, wR2 = 0.1001, and 4, monoclinic, P21/a, a = 1223.7(2), b = 586.0(1), c = 1446.3(3) pm, β = 97.81(2)°, R1 = 0.0459, wR2 = 0.1190, were determined by single crystal X-ray diffraction.