Silicon nitrogen compounds determination

Using a spatula, a crystal was removed from a flask containing a silicon-nitrogen compound and mounted onto the diffractometer. This crystal was the only one to be found in the flask. The space group was determined to be PI with half a molecule per asymmetric unit. The model from SHELXS shows a silicon atom and several other electron density maxima. Ten of those maxima form a familiar shape a Cp ligand, and can be assigned the atom type carbon. The model in file si-01.ins on the accompanying CD-ROM reflects this interpretation of the solution. 

HPLC is one of the most universal methods for determining the enantiomeric composition of substances and mixtures in a short time frame. Its application is not restricted to molecules in which chirality is based on a quaternary carbon atom with four different substituents it can also be employed for compounds containing a chiral silicon, nitrogen, sulfur, or phosphorus atom. Likewise, asymmetric sulfoxides or aziridines, the chirality of which is based on a lone electron pair, can be separated. Chirality can also be traced back to helical structures, as in the case of polymers and proteins to the existence of atropiso-merism, the hindered rotation about a single bond, as observed, for example, in the case of binaphthol, or to spiro compounds. 

The structures of compounds 55a,c and 56a,c were established by means of NMR spectroscopy and mass spectrometry. Due to the different polarity of the C=N and C=P triple bonds, the silicon ring atom in 55a,c is bound to the nitrogen atom, and in 56a,c to the carbon atom of the C=P moiety. The molecular structure of 55a was further determined by single-crystal X-ray diffraction analysis (Fig. 16).14 The four-membered SiNAsC framework is slightly puckered (folding angle N—Si—C/Si—C—As 7°), and... 

As can be seen from Table 1, not only the spectral data are quite different between pairs of compounds, but also the paramagnetism is decreasing when the carbon atom attached to the nitrogen is replaced by silicon, all other atoms being equal. As we have not been able to determine the molecular structures of the compounds until now, we cannot ascribe the change in properties to a definite change in structure. Nevertheless it seems obvious that the carbon or silicon atom in 6-position to the metal must have an important impact on the orbital-splitting at the transition element. 

Nitrogen in organosilicon compounds can be determined by the standard Kjeldahl method. Both silicon and nitrogen can be determined on the same sample by digesting it in concentrated sulfuric acid to which a drop of mercury has been added 18 the silica is filtered from the diluted acid, and ammonia is distilled from the filtrate after alkali sulfide and caustic solution have been added. The distilled ammonia is absorbed in standard acid, and the excess of acid is titrated in the usual manner. 

Finally, reaction of -butyl lithium with tris(tert-butylamino)silane prepared in high yield from trichlorosilane and excess tert-butylamine, gives the completely lithiated silazane 4. An X-ray structure determination shows the compound to be dimeric in the solid (Fig. 4). While six lithium and two silicon atoms build up the inner cube of a rhombic dodecahedron, six nitrogen atoms occupy the remaining vertices. Compounds with an analogous structure have been reported by several research groups [2, 7, 15]. 

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