| Abstract
| - Hydrogallation of 1,4-bis(trimethylsilylethynyl)benzene and 1,3,5-tris(trimethylsilylethynyl)benzene withdialkylgallium hydrides R2GaH (R = Et, nPr, iPr, neopentyl, tBu) afforded the corresponding additionproducts with intact GaR2 groups and two or three alkenyl substituents. In all products the gallium atomsattacked those carbon atoms that are attached to the trimethylsilyl groups. The expected cis arrangementof gallium and hydrogen atoms at the CC double bonds was detected only with di(tert-butyl)galliumresidues. Smaller alkyl groups gave the spontaneous formation of the trans-addition products. Cis/transisomerization is an inevitable step for the formation of effective chelating Lewis acids, and in particularthe trisalkene derivatives form interesting chalice-like hollows containing three Lewis-acidic centers attheir inner surfaces.
- The addition of Ga−H bonds to the C⋮C triple bonds of trimethylsilylethynylbenzenes afforded different types of products in which, depending on the steric demand of the substituents attached to gallium, the gallium and hydrogen atoms are on the same side or on different sides of the resulting CC double bonds. Only the trans products (Z,Z or Z,Z,Z) may be suitable to act as chelating Lewis acids.
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