With silicon-nitrogen bonds

The coupling of a trialkylsilane and an amine with loss of H2, catalyzed by palladium on carbon, was first reported by Sommer and Citron in 1967.178 More recent work by Laine and Blum has involved the application of catalytic dehydrocoupling of compounds containing Si-H and N-H bonds to form aligo- and polysilazanes. These polymers, with silicon-nitrogen bonds in the backbone, are useful precursors to silicon nitride. In the presence of Ru3(CO)i2, silicon-nitrogen bonds are cleaved and reformed... 

Recent developments in the chemistry of compounds with silicon-nitrogen bonds... 

Another modification of the double silylation process reported by Tanaka and co-workers involves the use of a bis(hydrosilane) instead of a disilane as the reactant molecule.61 This reaction can be described as a dehydrogenative double silylation, in that two Si-H bonds are activated rather than an Si-Si bond. The system is best catalyzed by Pt(CH2=CH2)(PPh3)2 other Pt, Pd, Ru, and Rh complexes give only very low yields of the double-silylated products. Alkynes, alkenes, and dienes undergo reaction with the bis (hydrosilane) with a range of results. Silicon-oxygen bonds and silicon-nitrogen bonds can also be formed by this method and are discussed in the appropriate sections later. 

Insertion of the Si=N bond into polar bonds is the most used reaction for the characterization of very reactive and transient silanimines. Especially, the reaction with alcohols is often the first reaction to be carried out with silicon-nitrogen multiple bond systems. Other reagents used for insertion reactions are amines, water and alkoxysilanes (equation 269)300,303,306,311,351-353. The insertion into E—X bonds (E = Si, Ge, Sn X = Cl, OR, NR2, N3) has been shown earlier in this review for the insertion into the Si—N bond of silyl azides310,351. A reaction reported is the insertion of 678 into the C—H... 

As mentioned in this chapter, in recent years much progress has been made in the chemistry of silicon-chalcogen multiple bonds. For silicon-sulfur doubly-bonded compounds, we have now several isolated examples, both kinetically stabilized and thermodynamically stabilized. Furthermore, there have been reports of the synthesis and characterization of stable compounds with silicon-nitrogen double bonds (i.e. silanimines or iminosilanes) as well as their heavier group 15 element analogues such as phosphasilenes and arsasilenes. 

The matrix technique allowed even the isolation of compounds with silicon-nitrogen triple bonds such as HSiN and HNSi12. 

An interesting example of an intermolecular complex is the trisilicon complex 194, in which only the central silicon is coordinated to the bidentate donor molecule225. The structure is a regular octahedron, with two tetrahedral termini. The silicon nitrogen bonds are rather short (2.012 and 1.991 A), and are comparable to those of octahedral intramolecular complexes (Table 23). 194 permits a comparison of Si—Cl bonds in a tetrahedral silicon moiety (2.03 to 2.07 A) with Si—Cl bonds trans to the dative bond in a hexacoordinate silicon (2.39 and 2.21 A). As expected, the latter are substatntially longer than the regular covalent bonds. 

Compounds containing the Si-N-P linkage combine the structural and stereochemical diversity of phosphorus with the reactivity of the silicon-nitrogen bond. Indeed, much of the derivative chemistry and synthetic potential of these compounds, especially the (silylamino)phosphines such as (Me3Si)2NPMe2, is based on this difunctional character. We report here a general, "one-pot" synthesis of (silylamino)phos-phines and describe their use in the preparation of several types of phosphorus-containing materials. 

Alkyl and Aryl Derivatives.—The cleavage of silicon-nitrogen bonds in A-silylphosphazenes by reactions with phosphorus and silicon halides has been studied in some detail. For example, with phosphorus trichloride a novel tri(phosphazenyl)phosphine is obtained ... 

Polydisilylazanes have been synthesized by the reaction of mixed disilanes with hexamethyldisilazane through silicon-chlorine/silicon-nitrogen bond redistribution reactions [10,26]. The formula [(CH3)2.6(Si2)i.oNHi.5]n was deduced during (reaction) at 250°C. 

Silica can be chlorinated, and the resulting product reacted with amines (1,2). Stationary phases prepared by this procedure contain a silicon-nitrogen bond, which is more stable than the silicon ester, but is still sensitive to hydrolysis. A better choice is the silicon-carbon bond, which is hydrolytically very stable. Chromatographic phases based on this bond can be prepared by reacting the silica with reactive silanes. Today s bonded phases are all based on silicon-carbon bonds. 

Such reactions are known to occur at about 2S0°C for monoaminosilanes reacted with a second type of amine [IS]. Amines incorporated in a polysilazane network require higher temperatures for the transamination because of steric hindrance and the necessity to cleave-rebuild simultaneously two Si-N bonds. Transition metal catalysts can reduce the temperature requirements. In early studies [16] of the transition metal-catalyzed polymmzation of silazanes, we observed the catalytic cleavage of Si-N bonds at temperatures below 1S0°C and the ability to metathesize silicon nitrogen bonds. The transamination reactivity occurs at temperatures below that of the carbonization and carbidization of the organic groups. 

Finally, silicon-nitrogen bonds are also labile in the presence of electrophiles, and this concept has been used by Komatsu in development of a silylimine linker (Table 1.16, Entries 12-14). Multifunctional cleavage was achieved with a range of electrophiles. For example, treatment with TFA left a hydrogen residual at the point of attachment (Table 1.16, Entry 12), while benzoyl (Table 1.16, Entry 13) and allyl (Table 1.16, Entry 14) groups were introduced by cleavage with benzoyl chloride and allyl iodide, respectively. 

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