Novel ways in the preparation of cyclic silicon-nitrogen compounds
INTRODUCTION Ofthe elements which tend to form ring compounds with another element, nitrogen needs a prominent mention. A variety of organic N-heterocycles, borazenes, phosphazenes, and sulphur nitrogen compounds areweil known. A large number of silicon-nitrogen ring compounds should be capable of existence as weil, however, only the six-membered ring-systems of cyclotrisilazane and the eight-membered ring-system of cyclotetrasilazane have been discovered so farla. Brewer and Haber1b obtained these systems for the firsttime in 1948 by reacting primary amines with dihalogenosilanes. Since we know many more Si-N ring-systems today the names chosen by Brewer and Haber which are still used everywhere are somewhat misleading and insufficient. In the present communication Si-N ring-systems are termed cyclosilazanes with the number and the position of the corresponding atoms placed before the syllables "sil" and "az" respectively. For cyclotrisilazane the proposed nomenclature is cyclo-1,3,5-trisil-2,4,6triazane, and cyclotetrasilazane willlikewise be called cyclo-1,3,5,7-tetrasil2,4,6,8-tetrazane. In all cyclosilazane structures known to date only Si N single bonds have been noticed. Doublebonds caused by (p-p)1T-overlap have not been observed. To what extent do the N-Si (~d)1T-bonds occur is not known so far but they are most likely to exist. The most common bond angles are 110° for N-Si-N and 130-135° for Si-N-Si, yet both angles can decrease to 90° in the four-membered ring-systems ofthe cyclodisildiazanes. The ring structure of the "cyclotrisilazane" is said to be planar, the structure of "cyclotetrasilazane" is puckered in the mode of an irregular crown 2.