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

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The compounds ClH2SiONMe2 and ClH2SiONEt2 have been prepared by the reaction of the corresponding O-lithiated hydroxylamines and dichlorosilane. Their identity has been proved by gas-phase IR and solution NMR (1H, 13C, 15N, 17O, and 29Si) spectroscopy. In contrast to ClH2SiONMe2, ClH2SiONEt2 is unstable at ambient temperature and decomposes to give H2SiCl2 and H2Si(ONEt2)2. ClH2SiONEt2 shows dynamic behavior in the solution as shown by low-temperature NMR. In the crystal ClH2SiONMe2 (low-temperature crystallography) is present as anti-conformer (torsional angle Cl−Si−O−N 180°) and shows an exceptionally small Si−O−N angle of 79.7(1)° and a Si···N distance of 2.028(1) Å, corresponding to a relatively strong Si−N-β-donor interaction. Ab initio calculations predict a wider Si−O−N angle of 91.6° (MP2/6-311G**). A gas-phase structure determination by electron diffraction shows the presence of two conformers (anti and gauche), which are equal in potential energy. The Si−O−N angle in the anti-conformer is 87.1(9)° and that in the gauche-conformer 104.7(11)° [Cl−Si−O−N torsion angle:  72.9(28)°]. Calculations (MP2/6-31G*) have shown the angle Si−O−N and the energy of the system to be largely dependent on the torsion angle Cl−Si−O−N, with a variation of the angle Si−O−N over a range of 30° during a full rotation of Cl−Si−O−N. Analysis of the calculated charges on the Si and N atoms show the β-donor interaction not to be simply caused by electrostatic interaction. Natural bond orbital analysis describes a lp-N → σ*Si - X type negative hyperconjugation as an important contribution to β-donor bonding. The silicon substituent in anti position to nitrogen exerts the major effect on the strength of the β-donor bond. Simultaneous analysis of negative hyperconjugation lp-O → σ*Si - X shows the Si−O−N compounds to have similar contributions to this interaction as H3SiOCH3 and questions negative hyperconjugation to be quoted in isolation for the rationalization of the wide bond angles in silyl ethers.

The synthesis and complete characterization of the family of tetra(amine)bisphosphine ligands (oNMe 2 C 6 H 4 ) 2 P-(X)-P(o-NMe 2 C 6 H 4 ) 2 , where X = CH 2 (dmapm), (CH 2 ) 2 (dmape), and CH(CH 2 ) 3 CH (dmapcp), are described. Crystal structure data are compared with known, analogous bisphosphines containing o-pyridyl or phenyl substituents in place of the o-dimethylanilinyl groups. Several short, intramolecular C-H···N distances in the anilinyl derivatives may represent the presence of weak hydrogen bonds.Résumé : On décrit la synthèse et la caractérisation complète d'une famille de ligands tétra(amine)bisphosphine, (o-NMe 2 C 6 H 4 ) 2 P-(X)-P(o-NMe 2 C 6 H 4 ) 2 , dans lesquels X = CH 2 (dmapm), (CH 2 ) 2 (dmape) et CH(CH 2 ) 3 CH (dmapcp). On a comparé leurs structures cristallines à celles de bisphosphines connues, analogues, contenant des substituants o-pyridyle ou phényle à la place des groupes o-diméthylanilinyles. Plusieurs distances intramoléculaires C-H···N dans les dérivés anilinyles sont courtes et elles peuvent être le reflet de la présence de faibles liaisons hydrogènes.

The compounds Cl 3 SiONMe 2 and Cl 3 GeONMe 2 have been prepared by reacting HONMe 2 with SiCl 4 and GeCl 4 , respectively, in the presence of the auxiliary base 2,6-dimethylpyridine. Their identity was proven by gas-phase IR and solution NMR spectroscopy of the nuclei 1 H, 13 C, 15 N, 17 O, 29 Si, by mass spectrometry and elemental analyses. The solid-state structure of Cl 3 SiONMe 2 was determined by low-temperature X-ray crystallography. The molecular structures of Cl 3 SiONMe 2 and Cl 3 GeONMe 2 in the gas phase have been determined by analysis of electron diffraction data augmented by restraints derived from ab initio calculations (MP2/6-31G*). The molecules adopt C s symmetry. Important gas-phase geometry parameter values for Cl 3 SiONMe 2 are: Si-O 1.623(3), Si-Cl in-plane 2.022(4), Si-Cl out-of-plane 2.024(2), O-N 1.479( 6) Å, Si-O-N 105.6(8), O-Si-Cl in-plane 104.2(3), O-Si-Cl out-of-plane 113.7(2)Њ, for Cl 3 GeONMe 2 : Ge-O 1.759(6), Ge-Cl in-plane 2.104(4), Ge-Cl out-of-plane 2.106(2), O-N 1.484(9) Å, Ge-O-N 104.0(11), O-Ge-Cl in-plane 108.9(20), O-Ge-Cl out-of-plane 111.6( 12)Њ. The structural data are interpreted in terms of weak attractive interactions between the nitrogen donor and the silicon/germanium acceptor atoms. The results are discussed in comparison with other structural data from the literature: the donor-acceptor interaction in Cl 3 SiONMe 2 is weaker than those in H 3 SiONMe 2 or ClH 2 SiONMe 2 , but stronger than that in Me 3 SiON(CF 3 ) 2 . Both compounds reveal stronger donor-acceptor interactions than the methyl analogues Me 3 SiONMe 2 .