Dissoziative ionisierung von 2-trimethylsilyl-1-phenoxyethan. Nachweis des nicht-klassischen ethylen-trimethylsilanium-ions in der gasphase

The mass spectrometric investigation of specifically deuterium and ¹³C labelled 2-trimethylsilyl-l-phenoxyethanes proves that the dissociative ionization of β-silyl-substituted ethane derivatives (loss of PhO^?; p-CH₃C₆H₄O^?; and C₄H^?₉ from PhOCH₂CH₂SiMe₃, p-MeC₆H₄OCH₂CH₂SiMe₃ and CH₃CH₂CH(CH₃)CH₂-CH₂SiMe₃, respectively) yields the non-classical bridge ethylene trimethylsilanium ion and not the open-chain isomer. Other stable C₅H₁₃Si^+? ions, characterised by collisional activation mass spectrometry, are the dimethyl n-propyl silicenium ion and the l-trimethylsilyl ethyl cation, both generated from the molecular ions of CH₃CH₂CH₂Si(Cl)Me₂ and CH₃CH(Cl)SiMe₃ via unimolecular loss of Cl^?.     

Supramolecular assemblies for light-induced electron-transfer reactions

In this paper, we present a summary of our work on highly photostable supramolecular ruthenium complexes, which may be incorporated into more complex systems for artificial solar energy conversion. We have used supramolecular chemistry and photochemistry to synthesize highly photostable ruthenium bipyridine coronates and a bipyridazine podate complex and to enhance photoelectron-transfer reactions in physical model systems for artificial photosynthesis. The recent progress of covalent and non-covalent sensitizer-relay assemblies for highly efficient photoelectron transfer is described.

A detailed mechanistic investigation of the binding behavior of cationic species to crow-ether-modified bipyridine derivatives is presented as an example of supramolecular binding in systems for photoelectron transfer. The host properties of the free ligands and the derived bis-heteroleptic ruthenium complexes are compared using UV—visible, luminescence quenching and proton nuclear magnetic resonance titrations. The combination of these three methods confirms that supramolecular binding of cations and the electron relay methylviologen (MV²⁺) to the complexes can be observed. The binding constants determined are of the order of (1–6) × 10⁴ 1 mol⁻¹ for the crown-ether ruthenium complexes and 1 × 10²−4 × 10³ 1 mol⁻³ for the crown-ether ligands. Single-photon-counting (SPC) investigations give strong indications for the coexistence of different binding mechanisms. The kinetic scheme of Yekta et al. has been adapted to interpret the binding mechanism.     

Reactions of Group 8, 9, and 10 monocations (Fe+, Co+, Ni+, Ru+, Rh+, Pd+, Os+, Ir+, Pt+) with phosphane in the gas phase

The reactions of Group 8, 9 and 10 monocations with phosphane were studied under single-collision conditions in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Fe(+) is completely unreactive, Co(+) reacts slowly and shows both adduct formation and P-H bond activation, and Ni(+) reacts slowly as well but shows adduct formation only. In contrast to their first-row congeners, the investigated second- and third-row transition metal monocations show facile P-H bond activations. Remarkably, extensive dehydrogenations of the collision complexes yield cations MPH(+), MP(2) (+), MP(3)H(+), MP(4) (+) and so on. Exceptional behaviour is shown by the two d(9) cations palladium (whose "dehydrogenation power" is rather limited) and platinum (which gives rise to a great manifold of only partially dehydrogenated species as well). Collision-induced dissociation experiments suggest that P(2) and PH units are formed as ligands.     

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.