Silyl hydrazine derivatives

Whereas the reaction of MCjNNHj with phosgene results in the formation of the urea, MejNNHCCOlNHNMej, protection with a silyl group prior to reaction with phosgene results in 

2MejNNH(SiMe3) + 2COClj ----------- Me jNN /r-C(0) jNNMe j + 2Me3SiCl + 2HCI 

An identical reaction product was obtained with Me2NN(SiMe3)j [1853] however, treatment of Me2NN(SiMe3)2 with phosgene at -30 C proceeded according to [2256]  

A clue to the reaction mechanism can be obtained by noting that the azoniaimidazolide (prepared by treatment of Me2NN(SiMe3) j with COF ) reacted with phosgene according to [2256]  

The Af-SiMe 3-substituted diazoies react with phosgene to give products which depend sensitively upon the reaction conditions [1409]. For example, where a substituted pyrazole is in an excess, the substituted urea is produced  

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Silicon derivatives of these simple amines have also been studied using /-irradiation in CFCI3 solution at 77 K. The radical cations 7 and 8 are formed in each of the cases. The EPR study showed that the singly filled MO of the radical cation was delocalized and extended into the silyl groups. The hydrazine derivative 9 also affords a radical cation... 

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 ... 

The only known diazasilacyclopropane was synthesized in 1982.56 As shown in Scheme 1, the bulky di-ter -butyl(fluoro)silyl group of the hydrazine derivative A, which is formed on reaction of monolithiated N,N -bis(trimethylsilyl)hydrazine 46 with di-/eri-butyldifluorosilane, reacts with excess 46 with formation of the diazasilyleyclopropane 115. 

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. 

Another possibility for the preparation of cyclodisilatetrazanes is salt elimination from lithiated A -silyl-A -fluorosilylhydrazines. The LiF elimination from the lithium derivates of the asymmetrical bis(silyl)hydrazines 23, 24, and 28 leads to the formation of the compounds 125-127 - [Eq. (38)1. 

Summary Mono(silyl)hydrazines condense to bis(silyl)hydrazines at higher temperature. The degree of oligomerization of mono- and dilithiated silylhydrazines in the crystal depends on the bulkiness of the substituents. Reactions of lithiated silylhydrazines with fluorosilanes lead, for example, to the formation of tetrakis(silyl)-hydrazines, six-, four- and five-membered rings. Formaldehyde derivatives of mono-(silyl)hydrazones are obtained in a reaction of mono(silyl)hydrazines with aqueous formaldehyde solution. 0-Silylpyrazolones can be synthesized by treating mono(silyl)-hydrazines with acetoacetic ester. A dipyrazolonesilane is formed in the reaction of an O-silylpyrazolone with dichlorodimethylsilane. 

The first stable monomeric formaldehyde derivatives are formed by reaction of mono(silyl)hydrazines with aqueous formaldehyde solution. 

Azodicarboxylate esters are the reagents of choice for electrophilic N-amino amination leading to hydrazine derivatives. Besides Grignard reagents and alkyl or aryl lithium compounds,enolates and silyl enol ethersderived from ketones have been aminated by this method. In particular, di-r-butyl azodicarboxylate has been reacted with a variety of chiral enolates (Scheme I9)i03->o and chiral silyl ketene acetds (Schemes 20 and to afford a-hydrazino acid derivatives with high dia-... 

Other groups that react with chloromethyleneiminium salts include hydroxylamines, hydrazines, oximes, imines, azines, anhydrides, imides and ketene O-alkyl-O -silyl acetal derivatives however, reactions with these compounds have been relatively infrequent. 

Fig. 2. Crystallization products of bis(silyl)hydrazine monolilhium derivatives.

This problem can be surmounted by the use of BTBSH, which affords the (V-silyl hydrazones cleanly and in high yield (eq 3). Thus, iV-silylated aryl and alkyl hydrazones are prepared hy reaction of l,2-bis(t-butyldimethylsilyl)hydrazine with an aldehyde or ketone in the presence of a catalytic amount of Sc(OTf)3 in dichloromethane (eq 3). A number of Lewis acid catalysts were explored, with Sc(OTf)3 being the most effective, giving the hydrazones in yields of up to 95% as mixtures of the syn- and anti-isomers. In the absence of Lewis acid catalysis, the reaction does not proceed. Unlike the simple hydrazine-derived hydrazones, the resulting iV-silyl hydrazones are stable, isolable, and capable of being stored for extended periods of time. 

Enders demonstrated that N-silylated SAMP hydrazine 105 can be used as a nucleophile in conjugate addition additions. For example, the lithiated tri-methylsilyl hydrazine derived from 105 was shown to undergo addition to... 

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