Hydrogen-rich isomeric cyclosilazanes are prepared-as single-source precursors for silicon nitride-by reaction of 1,1- and 1,2-dimethylhydrazine and 1,2-bis[(trifluoromethyl)sulfonyloxy]disilane, Tf-SiH2-SiH2-Tf. The molecular structure of N,N'-bis(dimethylamino)-2,3,4,5-tetrasilapiperazine (1) indicates peripheral Me2N --> SiH2 dative bonding.