Strong Intramolecular Secondary Si⋅⋅⋅N Bonds in Trifluorosilylhydrazines

Abstract

The simple silylhydrazines F(3)SiN(Me)NMe(2) (1), F(2)Si(N(Me)NMe(2))(2) (2), and F(3)SiN(SiMe(3))NMe(2) (3) have been prepared by reaction of SiF(4) with LiN(Me)NMe(2) and LiN(SiMe(3))NMe(2), while F(3)SiN(SnMe(3))NMe(2) (4) was prepared from SiF(4) and (Me(3)Sn)(2)NNMe(2) (5). The compounds were characterized by gas-phase IR and multinuclear NMR spectroscopy ((1)H, (13)C, (14/15)N, (19)F, (29)Si, (119)Sn), as well as by mass spectrometry. The crystal structures of compounds 1-5 were determined by X-ray crystallography. The structures of free molecules 1 and 3 were determined by gas-phase electron diffraction. The structures of 1, 2, and 4 were also determined by ab initio calculations at the MP2/6-311+G** level of theory. These structural studies constitute the first experimental proof for the presence of strong Si.N beta-donor-acceptor bonds between the SiF(3) and geminal NMe(2) groups in silylhydrazines. The strength of these non-classical Si.N interactions is strongly dependent on the nature of the substituent at the alpha-nitrogen atom of the SiNN unit, and has the order 3>4>1. The valence angles at these extremely deformed alpha-nitrogen atoms, and the Si.N distances are (crystal/gas): 1 104.2(1)/106.5(4) degrees, 2.438(1)/2.510(6) A; 3 83.6(1)/84.9(4) degrees, 2.102(1)/2.135(9) A; 4 89.6(1) degrees, 2.204(2) A.

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

“…[9] This phenomenon was therefore investigated with respect to the Si-C-N angle in 3, using self-consistent isodensity polarized continuum model (SCIPCM) calculations and geometry optimisations. Interactions between the molecule and the solvents benzene, acetone and water were assessed in terms of the resulting geometry of F 3 SiCH 2 NMe 2 .…”

“…This contradicts the expectations from earlier reports on geminal systems with SiCN units, which led to the postulate of SiCN three-membered ring systems with Si···N donor-acceptor bonds nor are the structural results in accordance with those for related compounds with Si-N-N and Si-O-N units, in which pronounced attractive forces have been found to exist between the geminal nitrogen atoms and the silicon atoms of the highly electrophilic SiF 3 groups. [8,9] We carried out bending potential calculations to find out how much energy is needed to distort the linking unit between the silicon and geminal nitrogen centres (the carbon atom of the CH 2 group in the case of F 3 SiCH 2 NMe 2 ) from its coordination geometry, which is assumed to be close to tetrahedral in the absence of attractive Si···N interactions. The calculations were performed on the basis of geometries fully optimised at the MP2/6-311G(d,p) level of theory with fixed Si-C-N angles.…”

“…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. However, some calculations on electronegatively substituted systems have predicted the compound FH 2 SiCH 2 NMe 2 to show deformation of this angle, [10] which could be the first proof of the existence of such an effect.…”

Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structures

“…More specific to the Si atom, there were some studies focused on the very weak Si/X (F, N, O) interaction also. [52][53][54][55][56][57] Unlike carbon compounds, organosilicon compounds have the potential to increase their coordination number to 5-and 6-coordinated Si centers and have been characterized by X-ray and nuclear magnetic resonance (NMR) spectroscopy. [58][59][60] Unfortunately, the weak Si/X interactions reported for stabilizing the particular conformations of small molecules in these pseudocoordinations are difficult to characterize by routine spectroscopic methods.…”

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

“…This work was done experimentally and theoretically by analysing model compounds including F 3 SiCH 2 NMe 2 , [6] (F 3 C)F 2 SiONMe 2 , [7] F 3 SiN(R)-NMe 2 (R = Me, SiMe 3 , SnMe 3 ), [8] MeHSi[ONA C H T U N G T R E N N U N G (BH 3 )Me 2 ] 2 [9] and ClH 2 SiONMe 2 . [10] It transpires that the composition of the spacer function is highly important for enabling or disabling a silicon-donor interaction.…”