LITHIUM-SALTS OF TRIS(TRIMETHYLSILYLAMINO)SILANE - THEIR STRUCTURES IN SOLUTION AND IN THE SOLID-STATE

Amides, which result from the reaction of tris(trimethylsilylamino)silane (Me3SiNH)3SiH (1) with n-butyllithium in the molar ratio 1:1 and 1:2 in nonpolar solvents, form a system in which the aminosilane 1, the monoamide (Me3SiNLi)(Me3-SiNH)2SiH (2a), the diamide (Me3SiNLi)2(Me3SiNH)SiH (3), and the triamide (Me3SiNLi)3SiH (4) are in equilibrium. When the monoamide 2a is dissolved in THF only the dimeric monolithiated THF adduct 2b is obtained. An X-ray structure analysis of the lithium silylamide 2b reveals that in the dimeric unit one of the lithium atoms is coordinated by THF, the two lithium atoms thus differing in coordination number (3 versus 4). An X-ray study of the triamide 4 reveals a centrosymmetric polycycle. Multipole interactions are formed between the lithium and the nitrogen atoms. The reaction of the diamide 3 with chlorotrimethylsilane in boiling THF yields the cis isomer of the cyclic diamide [(Me3SiNLi)(Me3-SiNH)SiN(SiMe3)]2.2 THF (5) as a byproduct. According to an X-ray structure analysis of 5 the lithium centers are coordinated by one oxygen and three nitrogen atoms, which form a strongly distorted tetrahedron. The interactions between lithium and nitrogen atoms N(1) and N(2), which are part of the four-membered Si2N2 cycle, have to be considered as weak on the basis of the remarkably long Li-N distances (233 and 243 pm).