β-Donor Bonds in SiON Units:  An Inherent Structure- Determining Property Leading to (4 + 4)-Coordination in Tetrakis-(N,N-dimethylhydroxylamido)silane

Abstract

Tetrakis(N,N-dimethylhydroxylamido)silane, Si(ONMe2)4 (1), and the analogous ethyl compound, Si(ONEt2)4 (2), have been prepared by the reaction of silicon tetrachloride with 4 equiv of the corresponding lithium N,N-dialkylhydroxylamide. The compounds have been characterized by elemental analysis, IR spectroscopy, NMR spectroscopy of the nuclei 1H, 13C, 15N [including the determination of 1 J(29Si15N) coupling constants], 17O, and 29Si, and nominal and high-resolution mass spectrometry. A crystal structure determination on 1 showed the molecule to be (4 + 4)-coordinate with short Si···N contacts [2.514(3)−2.555(3) Å] and narrow SiON angles [109.1° on average]. For comparison, the crystal structure of the isoelectronic Si(OCHMe2)4 (in situ grown crystal) was determined, showing the absence of β-donor interactions and an SiOC angle of 124.7(1)°. Ab initio calculations have been performed on the model compounds Si(ONH2)4 and H3SiONMe2 as well as the electronegatively substituted fluoro derivatives FH2SiONMe2 and F3SiONMe2 up to the MP2/6-311G** level of theory. Si(ONH2)4 is predicted to adopt C 2 symmetry and to have an SiON angle of only 109.5°, while the interactions in the other model compounds are predicted to be much stronger, as indicated by their SiON angles: H3SiONMe2 102.5°, FH2SiONMe2 90.0°, and F3SiONMe2 93.8°. The results are discussed with respect to the consequences of enlargement of the coordination sphere at the silicon atom, the unique chemical behavior of O-silylhydroxylamines (in particular their fast nucleophilic substitutions reactions), and the resulting use of this class of compounds in the silicone rubber industry.

A σ-hole interaction with radical species as electron donors: does single-electron tetrel bonding exist?

“…29 It was predicted that tetrel bonding interaction might play an important role in crystal materials and chemical reactions. [29][30][31] Recently, some theoretical studies have focused on the characteristics of the tetrel bonding interactions. 32,33 However, most of the Lewis bases in these tetrel-bonded complexes are related to neutral molecules and anions both with lone-pair electrons.…”

Hexakis(dimethylaminoxy)disiloxane: Insertion of an Oxygen Atom into the Si-Si Bond of a Disilane by Dimethylaminoxy Lithium

“…The 'H N M R shows a single line, while the splitting of the 13C NMR signal into a quartet of quartets proves the presence of the NMe2 group. The 15N N M R spectrum shows a singlet at -257.1 ppm, which is shifted to lower fre quencies as compared to Si(ONMe2)4 (-249.2 ppm) [8] or HSi(ONMe2)3 (-248.1 ppm) [9]. The signal in the 29Si N M R spectrum is found at -85.8 ppm, which is quite different from those in Si(ONMe2)4 (-73.7 ppm) and in Si(ONEt2)4 (-59.9 ppm), but similar to the value for Si(OiPr)4 at -85.7 ppm.…”

“…The silicon atoms should thus be seen as partially hypercoordinate and assigned 4+3-coordination, as in Si(ONMe2)4 [8] with 4+4-or HSi(ONMe2)3 [9] with 4+3-coordinate Si centres and similar Si-O-N angles.…”

Simple Silylhydrazines as Models for Si-Nβ-Donor Interactions in SiNN Units

“…Interactions between donor and acceptor centers separated by one atom only (two classical bonds) are well established in the chemistry of transition metal compounds, for example in the eightcoordinate systems [Ti(ONR 2 ) 4 ] with side-on-coordinated hydroxylamino ligands. [1,2] Our examples from p-block chemistry so far include systems containing SiON [3,4] and SiNN units, [5,6] both of which have relatively short Si´´´N distances and small Si-X-N angles (with X O, NR). To date, the strongest of these interactions has been detected in H 2 Si(ONMe 2 ) 2 , in which the Si-O-N angle is as small as 95.28 and the Si´´´N distance is only 2.30 .…”