Hydroalumination and Hydrogallation of 1,2-Bis(trimethylsilylethynyl)benzene: Formation of Molecular Capsules and C-C Bond Activation

Uhl W, Hepp A, Westenberg H, Zemke S, Wurthwein EU, Hellmann J

Abstract

Treatment of 1,2-bis(trimethylsilylethynyl)benzene with di-tert-butylaluminum and di-tert-butyl-gallium hydrides afforded the simple addition products 1,2-[(Me3Si)(R2E)C=C(H)]2C6H4 (R = CMe3; E = Al (1), Ga (2)), which could not be isolated in a pure crystalline form but have been characterized unambiguously by spectroscopic methods. Addition of the Lewis base ethyldimethylamine initiated condensation reactions which gave cage compounds (3 and 4) by the release of the corresponding tri-tert-butyl element derivatives. These cages contain two aluminum or gallium atoms which are bridged by three 1, 2-bis(trimethylsilylethenyl)benzene spacers to form molecular capsules. The metal atoms are further coordinated by terminal amino groups. The amino ligands could not be removed from the dialuminum compound 4 without decomposition, but the ligand-free gallium compound 5 was obtained upon heating of 3 (E = Ga) to 80 degrees C under vacuum. Thermolysis of the aluminum compound I in boiling n-hexane gave a unique reaction by the release of tri-tert-butylaluminum and the formal elimination of trimethylsilylethyne (decarbalumination). The product 6 is dimeric in the solid state via Al-C-Al bridges and has a pentacyclic molecular structure.