Klaus Angermund

Drei- oder Vierfach-Koordination des Aluminiums in Alkylaluminiumphenoxiden und deren Unterscheidung durch 27Al-NMR-Spektroskopie

The 27Al NMR spectra for a series of aryloxyaluminium compounds [RnAl(OAr)3−n]m (R  methyl, isobutyl; n  0–2; m  1, 2, 3) with various alkyl substituents in the 2 and 6 positions of the phenoxy rings have been measured. The δ(27Al) resonances give an indication of the number of aryloxy ligands and the coordination number of each Al atom. Monomeric R2AlOAr compounds have δ(27Al) resonances around 190 ppm whereas dimeric analogues give signals at 167 ppm. The 27Al NMR resonances for monomeric RAl(OAr)2 are found at ca. 100 ppm while those for [Al(OAr)3]2, where the aluminium atoms are solely bonded to aryloxy groups, lie at ca. 50 ppm. Characteristic shifts of the resonances were also observed for complexes of these compounds with THF, whereby it was found that the resulting change Δδ(27Al) decreases with increasing number of aryloxy ligands. The crystal structures of three selected compounds, 3, 8 and 11, were determined by X-ray crystallography.

The synthesis and crystal structure of Sn(C6H4CH2NMe2-o)2, and its reaction with Co(η5-C5H5) (η2-C2H4)2

Treatment of SnCp2 or SnCl2 with o-LiC6H4CH2NMe2 gave the new monomeric stannylene Sn(C6H4CH2NMe2-o)2 (1). The reaction between Co(η5-C5H5)(η2-C2H4)2 and the stannylene 1 yielded Co(η5-C5H5)(η2-C2H4)[Sn(C6H4CH2NMe2-o)2] (3). The crystal structure of 1 and 3 has been determined by X-ray diffraction. 1: C18H24N2Sn, a 10.096(1) A, b 10.056(1) A, c 17.665(1) A, β 95.37(1)°, space group P21/c (No. 14), Z = 4, monoclinic; R = 0.031 for 3402 observed reflections. 3: C25H33CoN2Sn, a 9.735(2) A, b 19.917(4) A, c 12.429(1) A, β 90.36(1)°, space group P21/a (No. 14), Z = 4, monoclinic; R = 0.046 for 4171 observed reflections. The geometry about tin in 1 is distorted ψ-trigonal bipyramidal, and that in 3 is distorted trigonal bipyramidal. Both of the C6H4CH2NMe2 ligands in 1 and 3 act as chelates by bonding of their nitrogen atom to tin.

Synthese, Struktur und Reaktivität von (tmeda)Ni(C2F4)

Abstract The reactions of Ni(cod) 2 (cod  1,5-cyclooctadiene), Ni(cdt) (cdt  trans , trans , trans -1,5,9-cyclododecatriene), and Ni(C 2 H 4 ) 3 with N , N , N ′, N ′-tetramethyl-ethylenediamine (tmeda) and tetrafluoroethene in ether yield almost quantitatively yellow needles of (tmeda)Ni(C 2 F 4 ) ( 1 ). 1 can also be obtained from the reaction of Ni(η 3 -C 3 H 5 ) 2 /tmeda or (tmeda)Ni(CH 3 ) 2 with C 2 F 4 . An X-ray diffraction study of the crystal structure of 1 confirms the trigonal-planar (or pseudo-square-planar) coordination of nickel by the tmeda and C 2 F 4 ligands. 1 reacts slowly with ethyne at 20°C to afford red-brown crystals of the nickelacyclopentene derivative (tmeda)Ni(CHCHC 2 F 4 ) ( 2 ).

The role of intermediate chain migration in propene polymerization using substituted {iPr(CpFlu)}ZrCl2/MAO catalysts

Comparison of pentad distributions obtained from NMR spectra and from a molecular mechanics-based modeling approach is performed for the catalysts {iPr(3-X-CpFlu)}ZrCl2 (X = H, Me, Et, iPr, tBu) at a range of different temperatures. In order to model the temperature dependency of the pentad distributions the variation in steric influence along with the change of the rotational energy level for catalysts with substituents displaying relatively low barriers to rotation is treated approximately by calculating energy profiles of 360° rotation of the alkyl groups. The temperature at which intermediate chain migration (back-skip) or chain epimerization starts to be important seems to be rather constant (30–50°C) among the five catalysts. Even in the case of X = tBu, back-skip seems to be unimportant for explaining the formation of isotactic polymer at room temperature.

‘Agostic’ metal–alkenyl β-CH interaction in (C5H4Me)2ZrCl(CHCMe)ZrCl(C5H5)2

For the title compound (C5H4Me)2ZrCI(CHCMe)ZrCI(C5H5)2(7), which was prepared by hydrozirconation of (C5H4Me)2ZrCI(CCMe)(6), an ‘agostic’ zirconium–alkenyl β-CH interaction was demonstrated by n.m.r. and X-ray diffraction studies.

Transition metal complexes IX. Nickel complexes with a chiral azaphosphole ligand

Abstract The reaction of (−)-(R)-myrtenal and (+)-(R)-phenylethylamine gave a Schiff base 1 which was reacted with MePBr2 in the presence of a base to give under dehydrohalogenation of an intermediate McCormack product a salt 2. Treatment of 2 with sodium led to the formation of the azaphosphole 4. η3-C3H5NiCl and 4 gave a 1:1 adduct 5 and nickel(0) gave a 1:4 complex 6. Compounds 4–6 were characterized by NMR spectroscopy as well as by single crystal X-ray structure determination.

Carbonylkomplexe “früher” übergangsmetalle: Darstellung und struktur von Cp2Zr(CO)[P(OCH3)3]

Abstract Thermolysis of zirconocene dicarbonyl at 50°C in toluene in the presence of an equimolar amount of trimethylphosphite produced dark green crystals of Cp2Zr(CO)[P(OCH3)3] (5) in about 50% isolated yield. 5 was characterized by NMR and IR spectroscopy (v(CO) 1849 cm−1) and by an X-ray crystal structure analysis. 5 crystallizes in the triclinic space group P 1 with cell constants a 8.351(1), b 14.347(2), c 14.876(1) A, α 68.256(5), β 75.978(5), and γ 85.87(1)°; Z = 4. Characteristic bond distances (for the two crystallographically independent molecules) are ZrCO 2.153(4), 2.167(5); CO 1.164(5), 1.149(7); ZrP 2.630(1), 2.619(1) A. Spectroscopic parameters of 5 are compared with those of 34 Group IV metallocene carbonyl complexes described in the literature.

Structure of interfacial water on fluorapatite (100) surface

The structure relaxation mechanism of the fluorapatite (100) surface under completely hydrated ambient conditions has been investigated with the grazing incidence X-ray diffraction (GIXRD) technique. Detailed information on lateral as well as perpendicular ordering corresponding to the water molecules and atomic relaxations of the (100) surface of fluorapatite (FAp) crystal was obtained from the experimental analysis of the CTR intensities. Two laterally ordered water layers are present at the water/mineral interface. The first layer consists of four water molecules located at 1.6(1) A above the relaxed fluorapatite (100) surface while the second shows the presence of only two water molecules at a distance of 3.18(10) A from the mineral surface. Thus, the first layer water molecules complete the truncated coordination sites of the topmost surface Ca atoms, while the second water layer molecules remain bonded by means of H-bonding to the first layer molecules and the surface phosphate groups. Molecular mechanics simulations using force field techniques are in good agreement with this general structural behavior determined from the experiment.

Competitive Adsorption of Glycine and Water on the Fluorapatite (100) Surface

The atomic structure of the aqueous glycine-fluorapatite (100) interface was investigated using grazing incidence X-ray diffraction. Experimental data analysis of crystal truncation rod intensities revealed detailed information on lateral as well as perpendicular ordering of the adsorbate molecules and the nature of atomic relaxations in the fluorapatite (FAp) (100) surface. Glycine and water molecules are arranged in two periodically ordered layers at the aqueous glycine-mineral interface. The adsorption process on the mineral surface is site competitive as both the glycine and water molecules show equal affinity toward surface Ca2+ cations. The glycine molecules interact directly with the FAp (100) surface, where one of their carboxylate groups coordinates with the surface Ca2+ cations. From the surface structure refinement, atomic positions of one glycine and four water molecules per unit cell were determined, along with the atomic relaxations in the FAp (100) surface. Molecular dynamic simulations were used to determine the long-range order of the adsorbate layers by investigating the hydrogen bonds.

Neue Bis(phosphan)-nickel(0)-alkin-Komplexe /New Bis(phosphane)-nickel(0)-alkyne Complexes

Abstract (Me3P)2Ni(C2H4) (5) and (dmpe) 2Ni2(C2H4)3 (6) react with various alkynes including ethyne (acetylene) and 1-alkynes to form the crystalline compounds (Me3P)2Ni(C2RR′), (dmpe)Ni(C2RR′), and (dmpe)2Ni2(C2R2)2 (R.R′ = H, Me, Ph). Structural assignments were made on the basis of 1H, 13C, and 31P NMR data. The crystal and molecular structure of (dmpe)Ni(C2Ph2) (17) has been determined by X-ray crystallography.