Tetra(alkylamino)silanes Si(NHR)(4) with R = Me, n-Pr, n-Bu, and i-Pr (1a-d) have been prepared via improved methods and characterized by complementary analytical and spectroscopic data. The reaction of 1a-c with 2 equiv of Tf-SiH2SiH2-Tf (Tf = trifluoromethylsulfonyloxy, "triflate") and triethylamine in toluene gives good yields of the spirocyclic compounds [(SiH2NR)(2)](2)Si (2a-c). 2a is obtained as a crystalline, but highly volatile? product (mp 35 degrees C, bp(0.05) 46-47 degrees C), the crystal and molecular structure of which has been determined by single-crystal X-ray diffraction methods (monoclinic, space group P2(l)/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 Id gives only low yields of the corresponding spirocycle ([SiH2N(i-Pr)](2))(2)Si, 2d. A silylammonium salt {[SiH2N(i-Pr)](2)Si-[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 P2(l)/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 Id and the 1,2-disilanediylbis(triflate) in the presence of NEt3 give good yields of the monocyclic compound [SiH2N(i-Pr)](2)-Si[NH(i-Pr)](2), 4. Compounds 1a-d and 2a-c 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.