Convenient high-yield syntheses for several open-chain and cyclic diaminodisilanes with fully hydrogenated Si-Si linkages are reported. The key intermediate for the preparation of the title compounds, 1,2-bis(((trifluoromethyl)sulfonyl)oxy)disilane (1), reacts with 2 equiv of diethylamine to afford a mixture of the isomers Et2NSiH2SiH2NEt2 (2a) and (Et2N)(2)SiHSiH3 (2a’). Isopropylamine and 1 give (Pr2NSiH2SiH2NPr2)-Pr-i-Pr-i (2b) exclusively. Treatment of 1 with 1 equiv of a primary alkylamine affords 2,3,5,6-tetrasilapiperazines [RNSiH2SiH2RNSiH2SiH2; R = Pr-i (3a), Bu-t (3b), Bzl (3c)] comprising two SiH2-SiH2 linkages. 1,3-Bifunctional bis(isopropylamino)silanes [((PrNH)-Pr-i)(2)SiR2; R = Me, Ph] were found to react with 1 to give trisilaimidazolidines [((PrN)-Pr-i)SiR2((PrN)-Pr-i)SiH2SiH2; R = Me (4a), Ph (4b)] again comprising the N-SiH2-SiH2-N unit. The crystal structures of N,N’-diisopropyl-2,2-diphenyl-2,4,5-trisilaimidazolidine (4b) and N,N’-di-tert-butyl-2,3,5,6-tetrasilapiperazine (3b) were determined in X-ray diffraction studies; the five-membered ring of 4b is nearly planar with all nitrogen atoms in a planar configuration. The six-membered ring of 3b has a twist conformation, but again with the two nitrogen atoms in a planar configuration. Surprisingly, the treatment of 1 with 1,4-bifunctional N,N’-dialkylethylenediamines [(RNHCH2-)(2); R = Pr-i, Bu-i] does not give the analogous six-membered-ring compounds but leads selectively to the isomeric five-membered heterocycles [(CH2NR)(2)SiHSiH3; R = Pr-i (5a), Bu-t (5b)], which are the products of a Si --> Si hydrogen shift rearrangement.