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

Abstract

N,N-Dimethylaminoxy)trifluorosilane, F 3 SiONMe 2 (1), was prepared by the reaction of LiONMe 2 with SiF 4 in Me 2 O at -96 °C as a colorless, air-sensitive liquid, which was identified by gas-phase IR spectroscopy and NMR spectroscopy of the nuclei 1 H, 13 C, 15 N, 17 O, 19 F, and 29 Si. 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-F in-plane 104.1(10)°, O-Si-F out-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-F in-plane 102.5(1)°, O-Si-F out-of-plane 118.0(1)°and 120.1(1)°].Using measured NMR chemical shifts in C 6 D 6 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 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. Losehand 7 investigated compounds with D (-NR 2 ) and A

Strong Intramolecular Secondary Si⋅⋅⋅N Bonds in Trifluorosilylhydrazines

“…Such large deviations between theoretical and experimental values for parameters directly connected to the non-classical geminal Si¥¥¥N interactions have previously been observed, and can only be overcome at very high levels of theory. [11,17] Unfortunatley, at present these cannot feasibly be applied to molecules of the size of compound 3. Although normally observed for silylated nitrogen atoms, the distortion of the coordination sphere from the ideal trigonal planar in 3 is impressive, and is the result of an attractive Si¥¥¥N interaction.…”

“…[11] Moreover, the strength of this interaction is extremely phase dependent, as was shown by subsequent structure determinations both in solution (Si-O-N 87.18) and the gas phase (94.1(9)8). As a result, polarity and polarizability of the surrounding medium has significant influence on the molecules.…”

N,N‐Dimethylaminopropylsilane: A Case Study on the Nature of Weak Intramolecular Si⋅⋅⋅N Interactions

“…We recently showed for (F 3 C)F 2 SiONMe 2 [7] and F 3 SiONMe 2 [18] that, despite the presence of relatively short Si···N distances and acute angles at the oxygen atoms in the three-membered SiON rings, the electron-density topology analysed in terms of the quantum theory of atoms in molecules (QTAIM) [19] describes these as open-chain systems. This means that no bond paths (bp) or bond critical points (bcp) between silicon and nitrogen atoms can be found in the electron-density maps, although the electron-density distribution and its features are similar to those of related non-cyclic silane-amine adducts along the SiÀN vectors.…”

(Dimethylaminomethyl)trifluorosilane, Me2NCH2SiF3—A Model for the α‐Effect in Aminomethylsilanes

“…The most intriguing examples are ClH 2 SiONMe 2 [7] and F 3 SiONMe 2 [8] for the SiON systems and F 3 SiN(SiMe 3 )NMe 2 and F 3 SiN(SnMe 3 )NMe 2 for the SiNN systems. [9] Our investigations into the SiCN systems have so far been restricted to the parent systems H 3 SiCH 2 NMe 2 [10] and Cl 3 SiCH 2 NMe 2 , [11] but these compounds do not show significant attractive interactions between the Si and N atoms, which would lead to compression of the Si-C-N angle.…”