HOMO AND HETERO METAL AMIDES OF TRIS-(TERT-BUTYLAMINO)METHYLSILANE - POLYCYCLES AND CLUSTERS WITH LI, NA, MG, AL AND TL

The hydrogen atoms attached to nitrogen in tris(tert-butylamino)methylsilane (1) can be substituted by metallic maingroup elements in a quite general way. If 1 is treated with trimethylaluminium apart from the monosubstituted product MeSi(tBuNH)(2)(tBuNA1Me(2)) (2) the trisamide MeSi(tBuNAlMe(2))(3) (3) is obtained. In similar ways complete substitution of the amino hydrogen atoms in 1 yields the compounds MeSi[tBuNMgN(SiMe(3))(2)](3) (6), [MeSi(tBuNLi)(3)](2) (10), and [MeSi(tBuNTl)(3)](2) (11), the later two being dimeric. If methylmagnesium iodide is allowed to react with 1 the intermediate MeSi(tBuNMgI)(3) (4) in some instances can be isolated as the THF adduct or may react with a further equivalent of the Grignard compound to generate the complex [MgI(THF)(5)]+ [MeSi(tBuNMgI)(3)CH3.THF](-) (5). The aluminium compound 2 has been used to access to heterometallic amides combining aluminium and sodium as in MeSi(tBuNA1-Me(2))(tBuNNa)(tBuNH) (7) or magnesium and aluminium as in the dimeric compounds [MeSi(tBuNA1Me(2))(tBuNH)(tBuNMgI)](2) (8) and [MeSi(tBuNA1Me(2))(tBuNH)(tBuNMgMe)](2) (9). X-ray structure analyses reveal 3 (tricyclic SiN3Al3 skeleton with Al-N distances from 2.014 to 2.025 Angstrom A), 6 (tricyclic SiN3Mg3 skeleton), and 7 [bicyclic SiN3AlNa skeleton with Na - N distances of 2.47(1) and 2.52(1)Angstrom A] to be monomeric even in the solid state. The compopunds 8 and 9 (both pentacyclic with spiro magnesium atoms) form centrosymmetric dimers by Mg-I-Mg and Mg-(CH3)-Mg bridges, respectively. The dimers 10 and 11 are completely different in terms of chemical bonding: while in the lithium compound 10 a centrosymmetric polycycle is formed by principly ionic interactions of the lithium atoms with corresponding nitrogen atoms, the centrosymmetric dimer in 11 is held together by Tl-Tl bonds. The X-ray structure analysis of 5 reveals the anion containing a Mg-coordinated CH3-.