Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The structural chemistry of a series of triaminosilanes XSi(NR<jats:sub>2</jats:sub>)<jats:sub>3</jats:sub> has been investigated in order to determine the ground‐state configuration and conformation of these molecules. Theoretical studies and analogy with the isoelectronic XP(NR<jats:sub>2</jats:sub>)<jats:sub>3</jats:sub> (X = CH<jats:sub>2</jats:sub>, O, Se, NSiMe<jats:sub>3</jats:sub> etc.) and P(NR<jats:sub>2</jats:sub>)<jats:sub>3</jats:sub> molecules suggest structures of C<jats:sub>s</jats:sub> or C<jats:sub>3</jats:sub> symmetry, with small energy differences between them. The molecular structure of HSi(NMe<jats:sub>2</jats:sub>)<jats:sub>3</jats:sub> <jats:bold>(1)</jats:bold> has been determined by a single‐crystal X‐ray diffraction study at low temperature. Surprisingly, the molecules have a non‐standard conformation with an irregular orientation of the three NMe<jats:sub>2</jats:sub> groups. The hydrido‐, chloro‐, methyl‐, and vinyltris(morpholino)silanes XSi[N(CH<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>O]<jats:sub>3</jats:sub> (X = H, Cl, Me, Vi; <jats:bold>2–5</jats:bold>) were prepared from the corresponding chlorosilanes and morpholine <jats:bold>(2, 3)</jats:bold> or lithium morpholide <jats:bold>(4,5)</jats:bold>. Their variable‐temperature NMR spectra were studied and the molecular structures determined by single crystal X‐ray diffraction. Compound <jats:bold>2</jats:bold> has a molecular geometry approaching mirror symmetry with one morpholino group significantly different from the other two. This structure resembles that of isoelectronic tris(amino)phosphines. Compounds <jats:bold>3–5</jats:bold> have structures with a propeller‐like arrangement of the three morpholino rings approaching C<jats:sub>3</jats:sub> symmetry for this part of the molecules. The chloro compound <jats:bold>3</jats:bold> shows the shortest Si‐N bond lengths (average 1.690 Å), followed by <jats:bold>2</jats:bold> (1.708Å),5 (1.709Å) and <jats:bold>4</jats:bold> (l.712Å). The configuration of all nitrogen atoms is almost planar, with sums of the angles close to 360°, and the morpholino rings adopt a chair conformation. According to the solution NMR spectra the ring inversion is slow at low temperature, but the rings rotate freely about the Si‐N bonds on the NMR time scale. The molecular structures are discussed in terms of steric and electronic effects of the substituents. Other model compounds, including (Me<jats:sub>2</jats:sub>N)<jats:sub>3</jats:sub>SiC<jats:sub>6</jats:sub>H<jats:sub>4</jats:sub>‐4‐Br <jats:bold>(6)</jats:bold>, MeSi[N(CH<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>)<jats:sub>2</jats:sub>NMe]<jats:sub>3</jats:sub> <jats:bold>(7)</jats:bold> and PhSi[N(CH<jats:sub>2</jats:sub>)<jats:sub>4</jats:sub>]<jats:sub>3</jats:sub> <jats:bold>(8)</jats:bold>, could not be crystallized, but were characterized by their analytical and spectroscopic data.</jats:p>