Organometallic Derivatives of Special Silazanes

In order to incorporate the metal alkyl or aryl in a ring system of nitrogen and silicon atoms, we have used, over the past 10 years, the well-known amines 25 (58) and 26 (59), or have developed synthetic routes to oxoamines 27 (60) 

The structures of compounds 31-54 may be deduced indirectly by spectroscopic methods (NMR, IR, or MS) or may be determined by X-ray crystallography. Frequently the structures found in solution are different from those existing in the crystalline state due to intramolecular bond fluctuations, as explained in Section III,D. 

The A11-C29-A12 and A11-N2-A12 bridges are almost symmetrical with an Al-C distance of 2.18(3) A and an Al-N distance of 1.99(1) A. As expected, the bond distances to the terminal atoms are remarkably shorter 64). Although C29 may be visualized as the center of a two-electron three-center bond, N2 uses two electron pairs to coordinate to the aluminum atoms. 

Compound 43 is a polycycle that can be derived from a cube having one corner missing (Fig. 4). The distortion from the point symmetry 3m (C3v) is small, the pseudo-threefold axis passing through the Si—C bond. All atoms of the ring have the coordination number four in a tetrahedrally distorted environment ((55). The Al-N distances are almost the same [2.02(1) A], whereas the Al-C distances are slightly shorter in the direction of the threefold axis [1.95(1) A] than those that are almost perpendicular to it [1.98(1) A]. The chelates 44-48 have been shown by cryoscopy in benzene to be monomeric. Their ring structure can be deduced from NMR spectra ( 5 5) (see also Section III,D). 

Of compounds 52-54, the aluminum and gallium derivatives have been fully characterized in the solid state by X-ray diffraction ( 52, 59). In Fig. 6, the 

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