CYCLOSILAZANES AS PRECURSORS OF SI3N4-CERAMICS

The products obtained in the reaction of 1-trimethylsilyl-2,2,4,4,6,6-hexamethylcyclotrisilazane 1 with butyllithium and fluorosilanes depend on the reaction conditions. Lithiated 1 reacts with SiF3N(SiMe3)2 at low temperatures to give the mono- and disubstituted compounds (2, 3) and the 1,3,5,7-tetraaza-2,4,6,8-tetrasilabicyclo-[4.2.0] octane 4. The permethylated bicyclus 5 is formed in the analogous reaction with MeSiF2N(SiMe3)2. At room temperature the monolithium salt of 1 reacts with SiF3N(SiMe3)2 to give the cyclodisilazane 6. 6 forms with butyllithium the lithium derivate 7. 7 reacts with SiF3N(SiMe3)2 to give 8, an isomeric cyclodisilazane of 3. In the reaction of lithiated 1 with Me2SiF2 the silylcoupled cyclodisilazane 9 is obtained, which is a suitable precursor of Si3N4 ceramics. The results of the crystal structure determination of 7 and the results of the pyrolysis of 9 are reported.