Twofold hydrogallation of C triple bonds c triple bonds by H-GaCl(2)-synthesis of chelating Lewis acids and their application in adduct formation.

The twofold addition of Ga-H to Ctriple bonds C triple bonds (hydrogallation) did not succeed by treatment of alkynes with an excess of dialkylgallium hydrides. In contrast, double hydrogallation was easily achieved by the reactions of H-GaCl(2) with trimethylsilyl-substituted alkynes [trimethylsilylphenylethyne and 1,4-bis(trimethylsilylethynyl)benzene] in appropriate stoichiometric ratios. The monoalkyne yielded the compound H(5)C(6)-CH(2)-C(SiMe(3))(GaCl(2))(2), 1, which was only sparingly soluble in n-hexane. Crystal structure determination revealed a dimeric formula unit possessing two parallel Ga(2)Cl(2) heterocycles in the solid state. Treatment of the dialkyne with four equivalents of the hydride gave a colorless precipitate, which was completely insoluble in hydrocarbons. Addition of diethyl ether to both products afforded soluble and monomeric etherates 1(OEt(2))(2) and 2 in which the two or four gallium atoms, respectively, were coordinated by ether molecules. Preliminary experiments with simple Lewis bases showed the principle capability of 1 to act as an effective chelating Lewis acid. Adducts of the type [H(5)C(6)-CH(2)-C(SiMe(3))(GaCl(2))(GaClX)(micro-Cl)]- (4-6) resulted upon treatment with halide ions (X = Cl, Br, I).