New heterometallic silylamides with polycyclic and cage-like structures

Abstract

The octamethyltrisilazane, Me2Si[N(H)SiMe3]2, can be used to ligade several metallic elements by substitution of the hydrogen atoms at nitrogen. In general it has been found that, in the absence of basic solvents, two octamethyltrisilazyl ligands act as a "chelating entity", coordinating a variety of metal centers. The formal charge in these centers is 4+. Simple displacement reactions allow the synthesis of a great variety of heterometallic silyl amides, a class of compounds until now only poorly described in the literature. The compounds can be classified by three general formulae: [Me2Si(NSiMe3)2]2-MIIIMI [MI=Li, MIII=Al, Fe, In; MI=Na, K, In, Tl, MIII=In), [Me2Si(N-SiMe3)2]2MIIMI2 (MII=Pb, MI=Li) and [Me2Si(NSiMe3)2]2MI2MI'2 (MI=Li, MI'=Tl). So far we have been able to synthesize only one compound with more than two octamethyltrisilazyl (omts) ligands: [Me2Si(NSiMe3)2]3Cd2Li2. The new compounds have been characterized by spectroscopic methods (1H-NMR, MS) and their solid state structures have been elucidated by singel crystal X-ray diffraction analyses. The metallic elements tend to optimize their coordination numbers by Lewis acid-base interactions with ligand nitrogen atoms, resulting in the formation of bicyclic, tricyclic, tetracyclic and cage structures. The greater the number of metallic centers present, the more the nitrogens are involved in coordination.