Ethylenediamine reacts with chlorosilanes to give N,N′-bis(silyl)ethylenediamines [(H2CNHSiRR′R″)2, 3: R, R′ = Me; R″ = CMe3; 4: R = H; R′, R″= CMe3; 5: R,R′ = CMe3, R″ = OH]. In the reaction of N,N,N′-tris(trimethylsilyl)ethylenediamine with SiF4 the difluoro-bis(1.1.4- tris(trimethylsilyl)ethylenediamino)silane (6) is obtained. The 1.3-diaza-2-silacyclopentanes R2Si[N(SiMe2R′)CH2]2, 7 - 10 (7: R = Cl, R′= Ph; 8: R = Cl, R′ = CMe3; 9: R = H, Cl, R′ = CMe3; 10: R = Br, R′ = CMe3) are isolated from the reactions of the corresponding bis(silyl)ethylenediamines and halosilanes in Et2O with NEt3 as HHal acceptor. Dilithium derivatives of N,N′-bis(silyl)ethylenediamines react with fluorosilanes with formation of the 1.3-diaza-2-silacyclopentanes, R2Si[N(SiMe2R′)CH2]2 (11 - 13) (11: R = F,R′ =Me; 12: R = F, R′ = CMe3; 13: R = CHMe2, R′ = Me). N-Fluoro-di(tert-butyl)silyl-N,N′-bis(trimethylsilyl)- ethylenediamine (14) is formed in the reaction of lithiated bis(trimethylsilyl)ethylenediamine with F2Si(CMe3)2. 8 reacts in amolar ratio 1:2 withNaNH2 or NaOMe with formation of 15 and 16, respectively · R2Si[N(SiMe2CMe3)CH2]2, 15: R = NH2; 16: R = OMe]. 1.3-Bis(tert-butyldimethylsilyl)- 2-tert-butyldimethylsiloxy-2-fluoro-1.3-diaza-2-silacyclopentane is the product of the reaction of 12 with LiOSiMe2CMe3. The crystal structures of 6 and 13 have been determined.