Synthese von borylgekoppelten Cyclotri- und -tetrasilazanen und viergliedrigen Cycloborasilazanen – Thermischer Abbau zu SiC und BN

Synthesis of Boryl-coupled Cyclotri- and -tetrasilazanes and four-membered Cycloborasilazanes – Thermal Decomposition to SiC and BN Dilithiated octamethylcyclotetrasilazane reacts with a difluoroboryl substituted cyclotrisilazane to give the BF coupled 6-8-6-membered cyclosilazane 1 , with Me₂SiHCl structural isomeric cyclotetra- and cyclotrisilazanes of the type I and II, and with Me₃SiCl structural isomeric cyclodisilazanes of the type III and IV are formed. The dilithium derivatives of the cyclosilazanes I and II as well as III and IV react with BF₃ and a BF₂-substituted cyclotrisilazane to give four-membered cyclo-borasilazanes which are coupled with a cyclodisilazane via a SiMe₂-group ( 2 – 4 ). The six-membered cycloborasilazane 5 is a byproduct in the reaction with BF₃. The reaction mechanisms are discussed. The pyrolysis with formation of SiC and BN and a crystal structure analysis were carried out with 1 .