Silazane cleavage

The silazane cleavage offers a rather convenient and versatile access to precursors containing a nitrogen bridge between the electropositive elements. 

Borazine-based Si/B/N/C polymers have been obtained by polycondensing H3N3B3(Cl)2Si(SiMe3)3 with hexamethyldisilazane [88]. Here once again silazane cleavage, forming the volatile chlorotrimethylsilane as a byproduct, is the driving process. 

SCHEME 18.24 Dehydrocoupling of mono-functional B-diethylborazine DEB and perhydridopolysilazane. As a side reaction (indicated by the dotted arrow), Si-N bond cleavage of the silazane backbone and formation of DEB-NHSiMej occnrs." ... 

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. 

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