SYNTHESIS OF BORYL-COUPLED CYCLOTRISILAZA NES AND TETRASILAZANES AND 4-MEMBERED CYCLOBORASILAZANES - THERMAL-DECOMPOSITION TO SIC AND BN

Dilithiated octamethylcyclotetrasilazane reacts with a difluoroboryl s ubstituted cyclotrisilazane to give the BF coupled 6-8-6-membered cycl osilazane 1, with Me2SiHCl structural isomeric cyclotetra- and cyclotr isilazanes of the type I and II, and with Me3SiCl structural isomeric cyclodisilazanes of the type III and IV are formed. The dilithium deri vatives of the cyclosilazanes I and II as well as III and IV react wit h BF, and a BF2-Substituted cyclotrisilazane to give four-membered cyc loborasilazanes which are coupled with a cyclodisilazane via a SiMe2-g roup (2 - 4). The six-membered cycloborasilazane 5 is a byproduct in t he reaction with BF3. The reaction mechanisms are discussed. The pyrol ysis with formation of SiC and BN and a crystal structure analysis wer e carried out with 1.