Hydrazines, lithium derivatives

Summary Fluorosilylamines and -hydrazines react with organolithium compounds to yield stable lithium derivatives. Perfluoro (Si-N) four- and six-membered ring systems are obtained with SiF4. The synthesis and crystal structures of the compounds are discussed. 

The reactions of azofurazans have been used to obtain the hydrazine and the amino derivatives. For example, reactions of azofurazans, including macrocyclic azofurazan 196, with BunLi and the lithium derivatives of methylfur-azans were studied. Several competitive processes were found to occur (1) the addition of a Li reagent at the N=N bond (2) the redox reaction giving rise to hydrazofurazans and (3) the reaction of the side chain of azofurazan (Scheme 44) <2004RCB615>. 

The new lithium derivatives 58-60 have been synthesized in the past few years59,60. Dilithiated hydrazine reacts with two equivalents of chlorodimethylphenylsilane to give... 

Because of the stability of the mono(silyl)hydrazines 3-8, their lithium derivatives can be used to synthesize asymmetric Af,AT -bis(silyl)hydraz-ines (23-40), as shown in Eq. (9). 

The condition for the formation of isomers is a side-on coordination of the lithium in 47, the lithium derivative of 27. Depending on the bulkiness of the fluorosilane, this side-on coordination makes possible a substitution that is suitable for the system. In comparison, the reaction of lithiated 27 with iPr2SiF2 leads only to the formation of the tris(silyl)hydrazine 75,16 so that kinetic control of the reaction must be supposed ... 

Another possibility for the preparation of cyclodisilatetrazanes is salt elimination from lithiated N-silyl-iV -fluorosilylhydrazines. The LiF elimination from the lithium derivates of the asymmetrical bis(silyi)hydrazines 23, 24, and 28 leads to the formation of the compounds 125-12715 32 [Eq. (38)]. 

Compound 126 crystallizes in a chair conformation. Because of the inversion center, the atoms N2, Sil, N2a, and Sila lie exactly in one plane. The atoms N1 and Nla are 47 pm above and below this plane, respectively. The sum of angles at N2 amounts to 359.8°. This nitrogen atom, in contrast to the NH-functional N1 with 349.9, is. vp2-hybridized. The angle Si2-N2-Sil of 140.7 is comparatively increased. The average Si—N and N—N bond distances are 175 and 148 pm, close to the expected values of 174 pm for Si—N and 145 pm for N—N.60 The same method of preparation, shown in Eq. (39), led to the formation of the first fluorosilyl functional hydrazine six-membered rings 127 and 128.43 The dilithiated bis(silyl)hydrazines 10 and 12 react with tetrafluorosilane to yield tetrakis-(silyl)hydrazines, which again react with the lithium derivatives. 

Hydrazine or its lithium derivative react with bis(halogenosilyl)amines in a 1 2 molar ratio to give a bicyclic compound 13357 [Eq. (42)]. 

The procedure outlined here160,11 closely resembles the methodology detailed in Section 7.1.1.1., except for the choice of nitrogen electrophile used, which in this case is the commercially available di-tert-butyl azodicarboxylate (DBAD). The reaction of the lithium derivatives of N-acyloxazolidinones 1 with DBAD affords diastereomerically pure (>300 1) hydrazines 2 in yields exceeding 90%1 a. 

Isolation. Diimide has been isolated by low-temperature (-196°, liquid Nj) condensation of the pyrolysis products of the lithium derivative of p-toluenesulfonyl hydrazine (2). This is prepared by the reaction of tosyl hydrazine with lithium bis-(trimethylsilyl) amide in benzene at room temperature. Pyrolysis of (2) is carried out under high vacuum (< I0" torr). 

The most usual reagent for the metallation of aldimines and ketimines and the corresponding hydrazines is LDA. The lithiations are generally carried out in mixtures of THF and hexane. The formation of the lithium derivatives, which proceeds rather smoothly at temperatures in the region — 30 to + 10 °C, is visible by the appearance of a yellow colour. The use of BuLi cannot be recommended, since addition of this reagent across the C=N bond may seriously compete with the deprotonation. 

The lithium derivative of bis(dimethylphenylsilyl)hydrazine crystallizes as lV,lV-bis(silyl) -hydrazide dimer. In this compound only end-on coordination is found for the lithium ions. 

An extensive series of fluorosilyl substituted amines, cyclosilazanes, and hydrazines have been prepared. Their stability and that of their lithium derivatives has been assessed, and the reactions with unsaturated compounds and with halides have been studied. ... 

Table 3. Addition of Mcthyllithium or Butyl-lithium to A.TV-Diinethyl Hydrazone Acetals 4 Derived from F.nantioinerically Pure Diols 3 Providing Hydrazines 54-5...

Chrysene, 45, 95 Cinnamaldehyde, 45, 36 48, 79 reaction with hydrazine, 47, 99 Cinnamic acids and derivatives, conversion to phenylcyclopropanes with lithium aluminum hydride,... 

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