[ScCl2{N(SiMe3)2}(THF)2] als Vorläufer für die Synthese von Scandiumnitrid

[ScCl₂{N(SiMe₃)₂}(THF)₂] – a Precursor for the Synthesis of Scandium Nitride [ScCl₂{N(SiMe₃)₂}(THF)₂] ( 1 ) has been prepared by the reaction of [ScCl₃(THF)₃] with the trisamide Sc[N(SiMe₃)₂]₃ in tetrahydrofurane solution forming colourless moisture sensitive crystals, which were characterized by a crystal structure determination. Space group P 1, Z = 2, lattice dimensions at –50 °C: a = 841.4(1), b = 924.2(1), c = 1550.0(1) pm, α = 90.046(7)°, β = 95.671(9)°, γ = 106.066(6)°, R₁ = 0.0329. In the molecular structure of 1 the scandium atom has a distorted trigonal‐bipyramidal coordination with the THF molecules in apical positions. At 400 °C 1 is converted into scandium nitride, ScN, by stepwise leaving of THF and ClSiMe₃.     

Phosphoraneiminato Complexes of Manganese and Cobalt with Heterocubane Structure

The phosphoraneiminato complexes [MnBr(NPEt₃)]₄ ( 1 ) and [M₄Br₅{NP(NMe₂)₃}₃] with M = Mn ( 2 ) and M = Co ( 3 ) are prepared by melting reactions from the anhydrous metal dibromides with the silylated phosphaneimines Me₃SiNPR₃ (R = Et, NMe₂) in the presence of potassium fluoride. All complexes are characterized by crystal structure analyses. 1 forms an only slightly distorted Mn₄N₄ heterocubane skeleton with an approximate T_d symmetry and short Mn…Mn distances of average 295.7 pm. In the structures of 2 and 3 one μ₃-NPEt₃ ligand of 1 is replaced by one bromine atom with μ₃-function. This leads to the novel heterocubane type M₄N₃Br with approximate C₃ symmetry. The deformation of the cubic skeleton leads to metal-metal distances of different lengths, i. e. 292.7 and 323.6 pm in 2 and 274.4 and 306.2 pm in 3 . Temperature dependent magnetic susceptibility measurements between 300 and 5 K on 1 have shown that strong antiferromagnetic coupling exists between the Mn(II) ions with S = 5/2, with a large negative Weiss constant of Θ = –694 K.     

Die Deprotonierung silylierter Amido-Komplexe von Seltenerdelementen

Deprotonation Reactions of Silylated Amido Complexes of Rare Earth Elements The deprotonation of the rare earth element-tris(bistrimethylsilyl)amides Ln[N(SiMe₃)₂]₃ of scandium, ytterbium, and lutetium with sodium-bis(trimethylsilyl)amide in THF leads to the complexes [Na(THF)₃LnCH₂SiMe₂NSiMe₃{N(SiMe₃)₂}₂] [Ln = Sc ( 1 ), Yb ( 2 ), and Lu ( 3 )]. According to crystal structure analyses of 1 and 2 the metal atoms Sc and Yb are constituents of planar LnCSiN four-membered rings. At the same time, the C atom of the CH₂ group is coordinated with the sodium ion in a linear axis Ln–C–Na; the sodium ion obtains a distorted tetrahedral arrangement by three THF molecules. The equatorial positions of the methylene-C atom, which is coordinated in a trigonal bipyramidal fashion, are occupied by the two H atoms and the Si atom of the four-membered ring. 2.6-dimethylbenzoisonitrile can be inserted into the Yb–CH₂ bond of 2 and the new five-membered heterocylce YbNCSiN originates, the exocyclic CH₂ group of which enters into a C–C coupling with the centrosymmetric dimer 4 while the ytterbium undergoes reduction. At the same time, sodium-7-methyl indolate is formed, which together with [NaN(SiMe₃)₂(THF)₂] forms the centrosymmetric dimeric molecular aggregate [NaN(SiMe₃)₂(THF)₂Na(C₉H₁₆N)]₂ ( 5 ). 1 : Space group P2₁/n, Z = 8, lattice dimensions at –80 °C: a = 2941.4(2), b = 1205.5(1), c = 2952.4(3) pm; β = 113.455(8)°; R₁ = 0.0625. 2 : Space group P2₁/n, Z = 8, lattice dimensions at –80 °C: a = 2943.9(1), b = 1219.5(1), c = 2944.3(1) pm; β = 113.372(4)°; R₁ = 0.0361. 4 : Space group P 1, Z = 4, lattice dimensions at –80 °C: a = 1117.0(1), b = 1207.5(1), c = 1614.3(2) pm; α = 73.634(10)°, β = 82.091(10)°, γ = 74.391(10)°; R₁ = 0.0525. 5 : Space group P2₁/n, Z = 2, lattice dimensions at –80 °C: a = 1126.7(1), b = 1459.3(1), c = 1741.1(1) pm; β = 96.461(8)°; R₁ = 0.0458. Quantum chemical DFT calculations of the scandium model compound [Na(Me₂O)₃ScCH₂SiMe₂NSiH₃{N(SiH₃)₂}₂] ( 1 M ) give a very large negative charge at the pentacoordinated carbon atom of the four-membered ring that is concentrated in a lone-pair orbital which has mainly p character. The carbon atom interacts with the positively charged scandium atom mainly by Coulombic interactions.     

Hexasupersilyl-triprismo-hexastannane (tBu3Si)6Sn6—The First Molecular Tin Compound Containing a Sn6 Prism

Dark violet hexastannane ( t Bu ₃ Si) ₆ Sn ₆ displays a new framework motif for molecular tin compounds, in which six Sn atoms are located at the corners of a trigonal prism. The compound can be synthesized according to Equation (a). R*=SitBu₃.     

Formation of Novel Dinuclear Mixed-Valence Rhodium Complexes by Intramolecular Migration of a Chelating Ligand

Significantly different coordination spheres are displayed by the two central atoms of 2 , the first representative of a novel type of mixed-valence dinuclear Rh⁰–Rh^II compound, which was synthesized from the stibane-bridged complex 1 . The Rh−Rh distance determined by an X-ray crystal structure analysis of 2 indicates a metal–metal interaction between the two metal centers.     

A Five-Membered Ring with Three Negative Charges and Solvent-Free Lithium Counterions

Remarkably short distances to the ring plane are shown by the η⁵-bound lithium ions in the first compound with a triply negatively charged five-membered ring, 1 , which was obtained by reduction of 2 with lithium. R=CH(SiMe₃)₂, Dur=2,3,5,6-tetramethylphenyl.     

Evaluation of Dead Time Calculation in Reversed-Phase Liquid Chromatography Using a Multiparametric Mathematical Method

In reversed phase liquid chromatography (RP-HPLC), the validity of a multiparametric non-linear least-squares regression iterative method for the determination of the column dead time t_M and the regression parameter (slope b), based on the use of alkan-2-ones, alkyl aryl ketones, and 1-nitroalkanes has been evaluated. The determination of t_M and b has been extensively studied for two mobile phase systems acetonitrile-water and methanol-water on seven octadecyl-C₁₈ and one octyl C₈ analytical columns. The calculated t_M and b values were compared with those obtained by Guardino's and Grobler's methods. The influence exerted thereon by the nature of the homologous series, the mobile phase composition, and the packing materials were investigated.     

ansa-Metallocene derivatives XXXIII. 2-Dimethylamino-substituted bis-indenyl zirconium dichloride complexes with and without a dimethylsilyl bridge: syntheses, crystal structures and properties in propene polymerization catalysis

Bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (2-(CH₃)₂N-C₉H₆)₂ZrCl₂, and dimethylsilyl-bridged bis(2-N,N-dimethylamino-indenyl) zirconium dichloride, (CH₃)₂Si(2-(CH₃)₂N-C₉H₅)₂ZrCl₂, were prepared by reaction of the corresponding ligand lithium salts with ZrCl₄ in toluene. Diffractometric structure determinations reveal C₂-symmetric complex geometries for both complexes. An increased electron density at the Zr center of the dimethylamino-substituted complexes is indicated by reduction potentials which are 0.3–0.4 V more negative than those of their unsubstituted analogs. When activated with methyl aluminoxane in toluene solution, (CH₃)₂Si(2-(CH₃)₂N-C₉H₅)₂ZrCl₂ catalyzes the polymerization of propene to polymers with a microstructure comparable with that of polymers produced with other Me₂Si-bridged bis(indenyl)ZrCl₂ complexes, but with a substantially increased fraction of i-propyl end groups derived from alkyl exchange between Zr-polymer and Al---Me species.     

Analysis of illicit drugs by nonaqueous capillary electrophoresis and electrochemical detection

Nonaqueous capillary electrophoresis (NACE) was applied to the determination of illicit drugs. The complete separation of amphetamine, methamphetamine, 3,4-methylene dioxy amphetamine (MDA), 3,4-methylene dioxy methamphetamine (MDMA), mescaline, cocaine and benzoylecgonine was obtained using an acetonitrile based buffer solution containing 10 mM sodium acetate and 1 M acetic acid. Electrochemical detection using a Pt microdisk electrode set to a potential of +1.8 V was found to be selective for MDA, MDMA and mescaline. The detection limits for these compounds were in the low ng/mL range which is between 2 and 3 orders of magnitude lower compared to UV-detection.     

Auxiliary controlled singlet-oxygen ene reactions of cyclohexenes

The photooxygenation of homochiral cyclohexene ketals, which are easily available from 2-cyclohexenone and l-tartrates, affords hydroperoxides and after reduction the corresponding allylic alcohols in good yields and high regioselectivities. This can be rationalized by electronic repulsions in a perepoxide intermediate and provides evidence for unfavorable 1,3 diaxial interactions with a dioxolane oxygen atom. Only low stereoselectivities were observed, due to the flexibility of the cyclohexene ring. However, the diastereomers could be separated and after cleavage of the auxiliary, 4-hydroxy-2-cyclohexen-1-one was isolated in enantiomerically pure form, which can serve as a building block for natural product synthesis.