Synthesis, structure and hydrolysis studies of dimethyltris(trimethylsilyl)methylmetallanes of aluminium and gallium

The reactions of [(Me3Si)(3)CLi . 2 thf] with Me2MCl (M = Al, Ga) afford the mixed trialkylmetallanes [(Me3Si)(3)CAlMe2 . thf] (1) and [(Me3Si)(3)CGaMe2 . thf] (2) in high yields. The coordinated THF molecule of compound 2 can be removed by sublimation in vacuo to yield the solvent-free product [(Me3Si)(3) CGaMe2] (3). Hydrolysis of compound 2 with one equivalent of water at 0 degrees C gives the trimeric hydroxide [{(Me3Si)(3) CGaMe(mu-OH)}(3)] (4), while the reaction with two equivalents of water at room temperature yields the unusually stable gallium hydroxide-water complex [((Me3Si)(3)CGaMe(OH)(mu-OH)MeGaC(SiMe3)(3)}. H2O . 2thf] (6). On heating, compound 6 is converted to the hydroxide [{(Me3Si)(3)C}(4)Ga-4(mu-O)(2)(mu-OH)(4)] (5), which has a heteroadamantane-like core. The hydrolysis of compound 1 with one equivalent of water at -25 degrees C gives the dimeric hydroxide [{(Me3Si)(3)CAlMe(mu-OH)}(2)2 thf] (7), while the reaction with two equivalents of water results in the formation of the novel hydroxide [{(Me3Si)(3)C}(4)Al-4(mu-O)(2)(mu-OH)(4)] (8), which is isostructural to the gallium com pound 6 with the adamantane-like struc ture. The molecular structures of compounds 1, 2, 4, 5 . 3 THF, 6, 7 and 8 . 0.5 THF have been determined by X-ray structure analysis. Compound 7 is the first structurally characterised aluminium hydroxide containing methyl groups, and 8 is the smallest structurally characterised galloxane hydroxide described in literature.