Silylhydrazine synthesis

Cyclic Silylhydrazines — Synthesis, Isomerizations, and Quantum Chemical Calculations... 

The synthesis of the first silylhydrazines was described in the 1950s51,52. In spite of the successful use of lithium hydrazides in preparative chemistry, the first structure analyses were carried out over 30 years later53,54. Nowadays dimeric, trimeric, tetrameric and hexameric hydrazides have been described53-58. 

The synthesis of the first cyclic and acyclic silylhydrazines were reported by Aylett9 and Wannagat et a/.101 in 1956-1958. Two main methods of preparation were developed. 

Bis(hydrazino)silanes are better stabilized with silyl groups bound to the nitrogen atoms. Although Zn-, Cd-, and Hg- connected silylhydrazines were described in 1970,52 silyl-substituted bis(hydrazino)silanes were not known until later. The first bis(hydrazino)silane that was silyl substituted at the terminal nitrogen atom and that showed no tendency to condensation was the terf-butyl-bis[iV,iV -bis(trimethylsilyl)hydrazino]phenylsilane 106, described in 1981.53 A decade later the synthesis of other stable bis(hydrazino)silanes was reported via different preparative methods using (a) mono-, (b) bis-, (c) tris-, and (d) tetrakis(silyl)hydrazines as precursors. 

The last section of this chapter deals with cyclic silylhydrazines. The synthesis of the first cyclic silylhydrazines were reported as early as 1958.55 Since then, a great diversity of such ring systems containing the Si—N—N unit have been synthesized. These can be classified as follows. 

Mono(silyl)hydrazines can also be used as precursors for the synthesis of five-membered silylhydrazine ring systems. In the reaction of the mono(silyl)hydrazine 7 with n-butyllithium in a 1 1 molar ratio, colorless crystals with a melting point of 184°C were obtained from n-hexane at 0°C. The reaction product did not contain the expected six-membered ring, but, as proved by NMR and IR investigations, consisted of the disilatriazole 121,15 as shown in Eq. (34). 

Mono(silyl)hydrazines can also be used as precursors for the synthesis of six-membered silylhydrazine ring systems. When 3 is lithiated it cyclizes above 5°C to give the six-membered ring 12413 [Eq. (37)]. 

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