Base-freie Tris(trimethylsilyl)methyl-Derivate des Lithiums,Aluminiums, Galliums und Indiums

Base-free Tris(trimethylsilyl)methyl Derivatives of Lithium, Aluminium, Gallium, and Indium Base-free LiR* (R*=-C(SiMe₃)₃) has been prepared from R*Cl and Li-metal in toluene at 85?90°C and used to synthesize the metallanes R*MMe₂ with M = Al, Ga and In, respectively. The NMR (¹H, ¹³C, ²⁹Si) and the vibrational spectra of these trisyl compounds have been discussed. AlCl₃ and LiR*(ratio 1 : 1) forms the metallate metallate Li[R*AlCl₃]. The triclinic unit cell (space group P1 ) consists of a centrosymmetric assoziate, formed by four Li[R*AlCl₃]- units with Al? Cl…?Li bridges, two pairs of Li-atoms differing in their chlorine-coordination and two disordered toluene molecules, inserted in the crystal lattice (R₁wR₂ =0,0444/0,1072). The reaction of GaCl₃ with LiR* (I :1) gives the unusual sesquichloride (R*Ga(Cl_1,33)Me_0,67)₃ in moderate yield. The X-ray structure determination shows a Ga₃Cl₃-skeleton with chairconformation and disordered, terminal gallium ligands (R₁/wR₂= 0,0646/0,2270).     

Few-electron corrections of statistical exchange potential in low-energy electron scattering

In order to allow for the relative increase of self-interaction in few-electron systems, a reduction factor is introduced into the statistical free-electron exchange potential. This net-exchange potential has been used in the calculation of elastic electron scattering by rare-gas atoms in the low-energy region from 0 to 10 eV. Whereas former attempts to treat these phenomena as simple potential scattering have failed, in this work at least a crude qualitative agreement with experimental data has been achieved in most cases.     

Probing cooperative effects in bimetallic clusters: indications of C-N coupling of CH4 and NH3 mediated by the cluster ion PtAu+ in the gas phase

The bimetallic cluster ion PtAu+ activates methane in the gas-phase, yielding the carbene PtAuCH2+ which further reacts with ammonia under C-N coupling. In contrast, neither Pt2+ nor Au2+ mediates C-N bond formation. This example demonstrates how bond activation in the gas phase can be tuned by cooperative effects in bimetallic clusters.     

Spectroscopic Studies of Cyclometallated Pd(II) and Pt(II) Complexes: Optical absorption and emission of single crystals of [Pd(thpy)2] and [Pt(thpy)2]

The polarized optical absorption and emission (spectra, decay times) of single crystals of [Pd(thpy)₂] and [Pt(thpy)₂] (thpy ≡ C(3′)-deprotonated form of 2-(2-thienyl)pyridine) at temperatures 1.9 K ? T ? 80 K are reported. The emission of [Pt(thpy)₂] can be influenced strongly by applied magnetic fields (0 ? H ? 6 T). Depending on the central ions Pd and Pt, the lowest excited electronic states of the single complexes are ligand-centered (LC) states and metal-to-ligand charge transfer (MLCT) states, respectively. This difference leads to distinctly dissimilar properties of the emission of both compounds. The experimental data show that the emission of single crystals of [Pd(thpy)₂] and [Pt(thpy)₂] at T ? 30 K originates from several types of traps (defect states of symmetry ³B₂?stabilized below the exciton band) with LC and MLCT character, respectively. In the Pt compound, the ³B₂ is split by spin-orbit coupling into three states. The states B and A, which determine the emission properties, are separated by Δv ～ 13 cm^?1. Both states can mix under the influence of an applied magnetic field yielding an increase of the emission intensity by a factor of ～ 1.5 at H = 6 T.     

Massenspektrometrische Untersuchung von Amiden: III—Intramolekulare Nucleophile Substitution bei der Methyl-Abspaltung aus Crotonsaurepiperidid und Vinylogen Derivaten

The methyl cleavage from piperidides of type CH₃(CH?CH)_nCONC₅H₁₀ with n = 1 to 3 does not proceed via ring contraction as shown earlier with n = 0. The fragmentation can be formulated with the concept of neighbouring group participation of the amide function which leads to a cyclic transition state. Investigations with a ²H-labelled compound in the case of n = 1 as well as energy measurements (AP, IP, E_k) agree with this assumption.