Silicon-nitrogen bond formation

Reactions (l)-(5) illustrate known methods for forming silicon-nitrogen bonds of potential use in the formation of oligo- and polysilazanes. The most common method of forming silazanes is via ammo-nolysis or aminolysis as shown in reaction (1) (4,5) ... 

A less explored area of transition metal catalysis involves bond formation between Group 14 elements and nitrogen. In direct analogy to previously discussed areas of research, silicon-nitrogen bonds can be formed by dehydrocoupling, hydrosilylation, and dehydrogenative silylation. The compounds produced are valuable for use in organic synthesis or as polymer precursors to silicon nitride ceramics. 

The formation of Si-N-B bond linkages has mostly been accomplished one of following methods so-called cleavage reactions, in which a silicon-nitrogen bond is cleaved by a covalent halide leading to the formation of some halosilane as a side product and dehydrohalogenation, in which the elements of a hydrogen halide are eliminated [17]. 

Another possihility is the oxidative addition of the N—H bond to the low-valent silicon center which results in the formation of a compound with a silicon—nitrogen bond. In 2006 Roesky et al. reported on the base-stabilized chloro silylene, [PhC(NfBu)2]SiCl (1), with a three-coordinate silicon center (2). Driess et al. described the silylene with the two-coordinate silicon, [CH (C=CH2) (CMe) 2,6-iPr2C6H3N)2 ]Si (2) (3). Both silylenes have the potential to activate N—H bonds. 

Silicon-carbon and silicon-nitrogen multiply bonded compounds 917 now gained acceptance as evidence for the intermediate formation of a transient silene. 

The class of phosphaalkenes with isolated P=C double bonds was first synthes ized by Becker.33 His synthetic strategy starting from trimethylsilylphosphines and acyl chlorides is still the most versatile (Protocol 3). The principle is based on the easily achievable, 1,3-silatropic migration of a silyl group bonded to phosphorus to a doubly bonded element such as nitrogen, oxygen, or sulfur. The process is favoured energetically by the construction of the P=C double bond with concomitant formation of a very stable silicon-element bond. 

Let us begin by considering the elements of the second and third periods (Li-Ne and Na-A). In each of these the orbitals available for bond formation are limited to four in number, namely, one s and three p orbitals, so that if four or more electrons are present it will be possible for all the orbitals to be filled by stable groups of electrons, as in the crystals of diamond and silicon or in the molecules of nitrogen, oxygen, fluorine, etc. Metallic properties in these two short periods will therefore be confined to the elements of the first three groups. 

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