Chalice-Type Tridentate Silicon Lewis Acids of C3 Symmetry in a Single Step Starting from Hexadehydrotribenzo[12]annulene.

Tridentate Lewis acids with aligned functions were synthesized based on the rigid framework hexadehydrotribenzo[12]annulene. The backbone and its fluorinated analogue were synthesised in one-pot syntheses, with alkyne deprotection and Sonogashira cross coupling reaction being carried out in one step. Hydrosilylation of the annulene with chlorohydrosilanes proceeded highly selectively and afforded rigid poly-Lewis acids with three SiCl3 or SiCl2 Me substituents perfectly oriented to one side of the molecule in a single step. The progress of hydrosilylation was investigated by time-correlated NMR spectroscopic studies. The crystal structures show that the framework is symmetrically functionalised and the silyl substituents are aligned in one direction. To increase the acidity of the Lewis acids the chlorosilyl substituents were fluorinated with SbF3 . Further investigation of hydrometallation reactions (M=B, Al, Ga, Sn) did not lead to corresponding structures.

Inter- and Intramolecular Aryl-Aryl Interactions in Partially Fluorinated Ethylenedioxy-bridged Bisarenes*.

Several ethylenedioxy-bridged bisarenes with a variety of type and number of aryl groups were synthesized to study non-covalent dispersion-driven inter- and intramolecular aryl-aryl interactions in the solid state and gas phase. Intramolecular interactions are preferably found in the gas phase. DFT calculations with and without dispersion correction show larger interacting aromatic groups increase the stabilization energy of folded conformers and decrease the intermolecular centroid-centroid distance. Single-molecule structures generally adopt folded conformations with short intramolecular aryl-aryl contacts. Gas electron diffraction experiments were performed exemplarily for 1-(pentafluorophenoxy)-2-(phenoxy)ethane. A new procedure for structure refinement was developed to deal with the conformational complexity of such molecules. The results are an experimental confirmation of the existence of folded conformations of this molecule with short intramolecular aryl-aryl distances in the gas phase. Solid-state structures are dominated by stretched structures without intramolecular aryl-aryl interactions but interactions with neighboring molecules.

Polyalkynylanthracenes--syntheses, structures and their behaviour towards UV irradiation.

A series of bis- and tris[(trimethylsilyl)ethynyl]anthracenes (1,5-, 1,8-, 9,10- and 1,8,10-) has been synthesised by multistep (cross coupling) reactions and the behaviour of the SiMe3-functionalised alkynylanthracene derivatives towards UV irradiation was qualitatively studied by NMR spectroscopy. In the case of 9,10-bis[(trimethylsilyl)ethynyl]anthracene we observed a photodimerisation upon UV irradiation; the third example was reported for a symmetrically 9,10-difunctionalised anthracene derivative, besides those with small fluorine- and methyl-substituents. The anthracene dimerisation is completely thermally reversible and the temperature dependence of the cycloelimination reaction was studied by (1)H VT-NMR experiments. The (deprotected) 1,5- and 1,8-diethynylanthracenes were converted with (dimethylamino)trimethylstannane to obtain the corresponding SnMe3-functionalised alkynes, potentially useful as highly conjugated building blocks in Stille cross coupling reactions. The new anthracene compounds were completely characterised by multinuclear NMR spectroscopy, (high resolution) mass spectrometry and - in most cases - by X-ray diffraction experiments.

Co-Crystal Formation of Partially Fluorinated 1,3,5-Tris(phenylethynyl)benzenes.

Several rigid 1,3,5-tris(phenylethynyl)benzenes with different fluorination patterns were synthesized through selective Sonogashira-Hagihara coupling reactions to analyze the packing behavior in solid-state structures. The aggregation is dominated by various intermolecular interactions between aryl substituents, triple bonds, C-H bonds and H⋅⋅⋅F contacts. Co-crystallization experiments for the analysis of preferred aryl-aryl-interactions led to 1 : 1 complexes. Intermolecular phenyl-perfluorophenyl interactions with short centroid-centroid distances are dominating these co-crystal structures. They lead to melting point increases of up to 49 °C for the co-crystals compared to the pure substances.