The Molecular Structures of Triaminosilanes

Abstract

Nitrogen planarity / SilanesThe structural chemistry of a series of triaminosilanes XSi(NR& 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& (X = CH2, 0, Se, NSiMe3 etc.) and P(NR2)3 molecules suggest structures of C, or C3 symmetry, with small energy differences between them. The molecular structure of HSi(NMe& (1) 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 NMe2 groups. The hydrido-, chloro-, methyl-, and vinyltris(morpholino)silanes XSi[N(CH,CH,),O], (X = H, C1, Me, Vi; 2-5) were prepared from the corresponding chlorosilanes and morpholine (2, 3) or lithium morpholide (4,5). Their variable-temperature NMR spectra were studied and the molecular structures determined by single crystal X-ray diffraction. Compound 2 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 3-5 have structures with a propeller-like arrangement of the three morpholino rings approaching C , symmetry for this part of the molecules. The chloro compound 3 shows the shortest Si-N bond lengths (average 1.690 A), followedby2 (1.?08A),5 (1.709A) and4 (l.?12A).Theconfiguration of all nitrogen atoms is almost planar, with sums of the angles close to 360", and the rnorpholino 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 (Me2N)3SiC6114-4-Br (61, MeSi[N(CH2CH2)2NMe]3 (7) and PhSi[N(CH,),], ( 8 ) , could not be crystallized, but were characterized by their analytical and spectroscopic data.

The Structural Chemistry of Aziridino- and Azetidinosilanes

“…[14] [15] This general pattern is priate lithiated heterocycles. still reflected in the most strained example of the silylaziridwith 50% probability ellipsoids, H-atoms omitted for clarity) [a] ines.…”

“…tetrachloride with slightly in excess of four equivalents of the appropriate lithiated heterocycles in diethyl ether at low As part of an ongoing investigation of poly(amino)silanes [14] [ 15] we have recently initiated a study of silicon de-temperature (Ϫ60°C). Compound 1 was obtained as a colorless, distillable liquid, solidifying at 8°C, while the homorivatives of aziridine and azetidine, mainly oriented towards a full structural characterization of prototype compounds, log 2 was obtained as a crystalline solid at room temperature, melting at 45°C.…”

“…The molecules have no crystallographically imposed symmetry owing to a propeller-type arrangement of the three phenyl groups at silicon (Figure 1). (7), NϪSiϪC21 107.03 (7), NϪSiϪC31 113.54 (7), C11ϪSiϪC21 109.74 (7), C11ϪSiϪC31 107.48 (7), C21ϪSiϪC31 111.17 (7), SiϪNϪC1 127.63(11), SiϪNϪC3 131.76 (12), NϪC1ϪC2 89.6(2), C1ϪC2ϪC3 88.3(2), C2ϪC3ϪN 89.7(2), C3ϪNϪC1 91.60 (14).…”

“…Tris(N-azetidino)silane (5) was accessiIntroduction the higher members of the homologous series of N-silylated, saturated N-heterocycles, albeit with strain-free five-and Aziridine derivatives of phosphorus have been extensively six-membered rings, respectively. While these and other studied owing to their widely established application in standard dialkylaminosilanes typically possess the much depharmacology and agriculture.[The most important bated planar configuration at nitrogen, [14] the aziridine or variants of this usage are based on cyclic phosphazene com-azetidine substituents are the only analogs where a steeply pounds in which all the phosphorus atoms are exclusively pyramidal configuration can be expected. This is also sugbound to nitrogen.…”

The Stereochemistry of Chloro-bis(N-morpholino)phenylsilane

“…In the course o f p ertin en t stu d ies o f m o rp h o lin osilanes [5,6] the title co m p o u n d w as p rep a re d and its stereo ch em istry investigated. A lth o u g h the stru c ture is generally straig h tfo rw ard , so m e d etails m erit special co m m en ts as show n in th is sho rt report.…”