Wide-Line NMR Study of Molecular Motion in [Me3SiNSiMe2

Abstract

Wide-line NMR and powder x-ray measurements were made on tetramethyl-N–N-bis(trimethylsilylcyclodisilizane) (Me3SiNSiMe2)2, over the temperature range 77°—300°K. Linewidths and second moments were calculated from the experimental NMR spectra. Theoretical second moments and line shapes were calculated for various motions, and then were compared with experimental results in order to determine the motions present. It was found that at 77°K the molecule is rigid except for rotation of the methyl groups about their C–Si bonds. At room temperature it was found that the molecule is rotating about a molecular axis, the Me3Si groups are rotating about their Si–N bonds, and the methyl groups are rotating about their C–Si bonds. All these motions were uncorrelated and of frequencies>106 cps. At intermediate temperatures various torsional oscillations were observed. The barriers to these motions were calculated and the relationships between the NMR results and the x-ray crystallographic data were discussed.