Cyclic silylhydrazines - Crystal structures of isomeric five- and six-membered rings

The lithium derivative of di(isopropyl)aminofluorosilylhydrazine cyclizes w ith formation of a five-membered silylhydrazine ring system (1). The analog ous reaction of di(tert-butyl)fluorosilylhydrazine gives the six-membered s ilylhydrazine ring system (2). 1 isomerizes thermally to the six-membered c yclic silylhydrazine 3. LiF-elimination from lithiated (Me3C)(2)SiFNHNHSiF( CHMe2)(2) leads to the formation of the six-membered cyclic silylhydrazine 4, [(Me2HC)(2)Si-NH-NSiF(CMe3)(2)](2) Symmetrical six-membered tetra(fluoro )silylhydrazine rings, (F2SiNRNR)(2) (5: R = SiMe3, 6: R = SiMe2CMe3) are o btained in the reaction of bis(trifluorosilyl)hydrazines with dilithium-bis (silyl)hydrazides, whereas a five-membered unsymmetrical silylhydrazine (7: (RNSiF2)(2)N-NR'(2), R = SiMe2CMe3, R' = SiMe3) is formed in the reaction of R(SiF3)N-N(SiF3)R and R'(Li)N-N(Li)R'. In the reaction of the same fluor osilylhydrazine with dilithiated N,N'-diphenylhydrazide the unsymmetrical s ix-membered ring 8 is obtained. The crystal structures of 1, 2 and 3 are re ported.