(N,N-Dimethylaminoxy)trifluorosilane:  Strong, Dipole Moment Driven Changes in the Molecular Geometry Studied by Experiment and Theory in Solid, Gas, and Solution Phases

• Published in: Journal of the American Chemical Society 2000-05, Vol.122 (18), p.4471-4482
• Main Authors: Mitzel, Norbert W, Losehand, Udo, Wu, Anan, Cremer, Dieter, Rankin, David W. H
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja994542w

(N,N-Dimethylaminoxy)trifluorosilane, F3SiONMe2 (1), was prepared by the reaction of LiONMe2 with SiF4 in Me2O at −96 °C as a colorless, air-sensitive liquid, which was identified by gas-phase IR spectroscopy and NMR spectroscopy of the nuclei 1H, 13C, 15N, 17O, 19F, and 29Si. The gas-phase geometry of 1, as determined by electron diffraction analysis refined in C s symmetry, is influenced by weak attractive interactions between Si and N:  Si···N 2.273(17) Å, Si−O−N 94.3(9)°, [Si−O 1.619(8) Å, N−O 1.479(7) Å, O−Si−Fin - plane 104.1(10)°, O−Si−Fout-of - plane 111.8(10)°]. X-ray diffraction analysis of 1 reveals that intramolecular Si···N interactions are much stronger in the solid state than in the gas phase:  Si···N 1.963(1) Å, Si−O−N 77.1(1)° [Si−O 1.639(1) Å, N−O 1.508(1) Å, O−Si−Fin - plane 102.5(1)°, O−Si−Fout-of - plane 118.0(1)° and 120.1(1)°]. Using measured NMR chemical shifts in C6D6 solution, the geometry of 1 in solution was determined with the NMR/ab initio/DFT-IGLO method to fall between that of the gas-phase geometry and the geometry in the solid state. MP2 and DFT calculations reveal that electrostatic interactions between 1 and the surrounding medium increase with the dielectric constant ε since mutual charge polarization enhances the molecular dipole moment from 4 to more than 6 D, which implies a compression of the Si−O−N angle and the Si···N distance. Since electrostatic attraction between N and Si supports these changes, the increase in molecular energy upon reduction of the Si···N distance is small and compensated by the gain of stabilizing intermolecular interactions. The analysis of the calculated electron density distribution shows that the main aspects of bonding in 1 are not changed in the solid state and that the Si···N attraction is not of covalent nature, but rather due to strong electrostatic and dipole interactions.