Silazanes synthesis

Introductory Remarks. In contrast with the popularity and usefulness of the polysiloxane chains, which constitute the structural backbone of silicones, the knowledge of polymers based on the silazane unit is still limited. In the sixties there was still some hope of the possibility of producing long chain polysilazane molecules and a number of laboratories were active in seeking convenient methods for their synthesis (e.g. see review by Aylett (12)). 

New Silazane Oligomers and Polymers with Organic-Inorganic Main Chains Synthesis, Properties and Application... 

The synthesis of 1,3,5,2,4-trithiadiazepine 79 was realized in <1997CBR247> by two methods - from bis(trimethyl-silazane) derivatives 80 and disulfenyl chloride 81 (Scheme 14). 

The presence of two rather than three Cp rings around the trivalent uranium centers seems to provide an optimum stability to the complex. The synthesis of the Cp UI2(thf)3 and Cp 2UI(thf) was achieved in high yield upon treatment of UI3(thf)4 with the appropriate amount of Cp K (Scheme 17). Further functionalization of Cp UI2(thf)3 was obtained via a metathetic reaction with silazanate. The crystal structure of the resulting Cp U[N(SiMe3)2]2 showed the presence of agostic interactions between the U center and the methyl groups of the silazanate moiety (47). 

The reductive-trimethylsilylation, via either a chemical (Li/HMPA/THF) or an electrochemical (undivided cell/sacrificial anode) process, led to the synthesis of 1-(trimethylsilyl)alkylamines (RSMAs).191 Thus, l-(trimethylsilyl)f-amylamine was prepared in 67% yield from pivalaldehyde iV-(trimethylsilyl)imine, after hydrolysis of the intermediate silazane. 

The examination of structure/property relations of molecular educts and resulting ceramics required the synthesis of stoichiometrically and stmcturally different precursors. A variety of synthesis routes for Si-B-N-C precursors fiom organosilanes, silazanes, and boron compounds have been reported in recent years [3 - 5]. As an example, Riedel obtained a polymeric precursor via hydroboration of methylvinyldichlorosilane and subsequent condensation of the hydroboration product with ammonia (Eq. 1). Pyrolysis led to silicoboron carbonitride ceramics exhibiting thermal stability up to 2000 °C [6]. 

Two general methods are suitable for the synthesis of permethylaminocyclohexasilanes [5]. As shown in Scheme 2, the reaction of 1 with NH3 or Na/NHs, respectively, cleanly affords aminoundecamethylcylohexasilane (9), which can be further silylated yielding the silazanes 10 and 11 after lithiation with n-BuLi. The air-stable compound 12 is obtained in good yield ftom 1 and LiN(SiMe3)2-... 

The most important representative of the silazanes is hexamethyldisilazane, which is utilized in large quantities for the introduction of protective groups in the synthesis of pharmaceuticals and for hydrophobizing fillers, in particular silicates. It can be easily produced by reacting trimethylchlorosilane with ammonia ... 

Progress in synthesis and application of silazanes, particularly, cyclo-silazanes 07CJO1358. 

The results of the investigated cross-metathesis reactions of silicon containing norbomene derivatives with ethylene showed a poor reactivity for some substituents. Reactive chlorosilanes act as catalyst poisons and silazanes diminish the catalyst s activity by coordination of nitrogen to the metal center. Starting from norbomene derivatives with alkoxy-substituted silicon moieties, a selective synthesis of new silicon-containing a,(0-dienes could be accomplished (Scheme 2). 

The second approach which generates poly(fi-aminoborazines) is based on the reaction of 5-chloroborazine derivatives with linking reagents such as silazanes in an one-step synthesis procedure. The earliest successful efforts to prepare poly[5-aminoborazine] according to this one-step synthesis procedure are those made by Paine et al. [38] They have synthesized a large variety of polymers by reaction of 5-chloroborazine derivatives with disilazanes. 

Scheme 16 Synthesis of styrene-silazane block copolymer.

There are a number of published reviews on the synthesis of poly-silazanes. - " The present discussion is limited to a brief history and development of oligo- and polysilazane synthesis. The methods of synthesizing polysilazanes include (1) polymerization by aminolysis (or ammonolysis) of chlorosilanes, (2) ringopening polymerization of oligomeric cyclosilazanes, (3) deamination and condensation of bis- and tra-aminosilanes, (4) redistribution polymerization of chlorosilanes and aminosilanes, and (5) catalyzed dehydrocoupling of diamines and organosilanes. 

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