REACTION-MECHANISMS IN THE SILICON-NITROG EN CHEMISTRY - ISOMERIC CYCLODISILAZANES AND CYCLOTRISILAZANES

Mono- (1) and ert-butyldifluorosilyl)-hexamethylcyclotrisilazane (2) a re obtained in the reactions of lithiated and dilithiated hexamethylcy clotrisilazane with CMe(3)SiF(3) in a molar ratio 1:1 and 1:2. The lit hium derivative of 1 (1a) reacts with CMe(3)SiF(3) also to give 2 at - 50 degrees C and with Me(2)SiF(2) to give 3. Instead of 2 the structur e isomeric cyclodisilazane 4 is formed at room temperature. The four-m embered ring 2,2,4,4-tetramethyl-3-trimethylsilycyclodisilazane (6) is formed in the reaction of the six-membered ringanion la and chlorotri methylsilane. 4 reacts with C4H9Li to give the lithium derivative 4a. 4a is also formed from lithiated 2 (2a) by ring contraction. Isomerism with formation of the lithiated cyclodisilazane 3a also occurs in the reaction of 3 and C4H9Li 3a forms via Li ... F contacts a polymeric l attice in the crystal. In the reaction of the dilithiated 1 (1b) and C Me(3)SiF(3) the 3,5-tris(tert-butyldifluorosilyl)-cyclotrisilazane 7 i s obtained. In the reaction of 4a with CMe(3)SiF(3) and of 3a with C6H 5SiF3 substitution occurs, 8 and 9 are obtained. 3a and 4a react therm ally with LiF-elimination and formation of cyclobutyl)silyl]-1,3-diaza -2,4-disilacyclobutanes 10 and 11. The reaction mechanisms of the ring contractions are discussed.