Bis(trimethylsilyl)ammonium salts obtained by reaction of hexamethyldisilazane with TiCl4, ZrCl4, or SnCl4

The reaction of hexamethyldisilazane with TiCl4 in CH2Cl2 leads to the formation of [(Me3SiNTiCl2)(8)] (3). According to the crystal structure analysis, 3 is an octameric titanium trimethylsilylimido chloride. The mechanism of the formation of 3 was studied in detail by means of time-dependent N-14 NMR spectroscopy. [(Me3Si)(2)NTiCl3] was identified as an intermediate during the formation of 3. Two by-products were identified: [(NH4)(2)TiCl6] and the hitherto unknown bis(trimethylsilyl)ammonium salt [(Me3Si)(2)NH2](+)[Ti2Cl9](-) (5). According to the crystal structure analysis, protonation of hexamethyldisilazane to give the cation of 5 causes a significant lengthening of the Si-N bond from 173.5 to 186 pm. Other tetravalent metal chlorides, such as ZrCl4 and SnCl4, also reacted with hexamethyldisilazane to yield bis(trimethylsilyl)ammonium salts. However, the constitution of the corresponding anions differs significantly. In the case of ZrCl4, an anionic chlorotrimethylsilylimidozirconate (6) [(Me3Si)(2)NH2](2+) [{Cl3ZrCl3Zr(Cl)(NSiMe3)}(2)](2-) was obtained, while SnCl4 reacted to give a novel spiro anion [N(SnCl3)(2)(SnCl2)(4)-(NSiMe3)(2)(NH)(2)](-) together with the bis(trimethylsilyl)ammonium ion in 7; this anion is the first species containing a tetrastannylated nitrogen.