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Binary Si/N-[4.4]-Spirocycles with Two SiH2SiH2 Loops

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journal contribution
posted on 16.01.1998, 00:00 by Marcus Söldner, Annette Schier, Hubert Schmidbaur
Tetra(alkylamino)silanes Si(NHR)4 with R = Me, n-Pr, n-Bu, and i-Pr (1ad) have been prepared via improved methods and characterized by complementary analytical and spectroscopic data. The reaction of 1ac with 2 equiv of Tf-SiH2SiH2-Tf (Tf = trifluoromethylsulfonyloxy, “triflate”) and triethylamine in toluene gives good yields of the spirocyclic compounds [(SiH2NR)2]2Si (2ac). 2a is obtained as a crystalline, but highly volatile, product (mp 35 °C, bp0.05 46−47 °C), the crystal and molecular structure of which has been determined by single-crystal X-ray diffraction methods (monoclinic, space group P21/n, Z = 8). The lattice contains two independent molecules in the asymmetric unit, which have very similar dimensions. The two five-membered rings are almost planar and close to perpendicular to each other. Owing to sterical hindrance, the analogous reaction of 1d gives only low yields of the corresponding spirocycle {[SiH2N(i-Pr)]2}2Si, 2d. A silylammonium salt {[SiH2N(i-Pr)]2Si−[NH(i-Pr)]−[NH2(i-Pr)]}+Tf- (3) is produced as a major product. Compound 3 is one of the very few silylammonium salts as confirmed by a full structural analysis (monoclinic, space group P21/c, Z = 4). In the crystal, 2 equiv are grouped together as a centrosymmetrical cluster of two cations and two anions with hydrogen bonds between the amino/ammonio and the sulfonate groups. Equimolar quantities of 1d and the 1,2-disilanediylbis(triflate) in the presence of NEt3 give good yields of the monocyclic compound [SiH2N(i-Pr)]2Si[NH(i-Pr)]2, 4. Compounds 1ad and 2ac are hydrogen- and silicon-rich precursor molecules for the production of silicon nitride in pyrolytic, plasma- or laser-induced (thermal) decomposition and for the preparation of silazane networks and gels by controlled aminolysis or by metathesis of the Si−Si bonds.