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

Abstract

N,N-Dimethylaminopropylsilane H(3)Si(CH(2))(3)NMe(2) was synthesised by the reaction of (MeO)(3)Si(CH(2))(3)NMe(2) with lithium aluminium hydride. Its solid-state structure was determined by X-ray diffraction, which revealed a five-membered ring with an SiN distance of 2.712(2) A. Investigation of the structure by gas-phase electron diffraction (GED), ab initio and density functional calculations and IR spectroscopy revealed that the situation in the gas phase is more complicated, with at least four conformers present in appreciable quantities. Infrared spectra indicated a possible SiN interaction in the Si-H stretching region (2000-2200 cm(-1)), as the approach of the nitrogen atom in the five-membered ring weakens the bond to the hydrogen atom in the trans position. Simulated gas-phase IR spectra generated from ab initio calculations (MP2/TZVPP) exhibited good agreement with the experimental spectrum. A method is proposed by which the fraction of the conformer with a five-membered ring can be determined by a least-squares fit of the calculated to experimental absorption intensities. The abundance of this conformer was determined as 23.7(6) %, in good agreement with the GED value of 24(6) %. The equilibrium SiN distance predicted by theory for the gas-phase structure was highly variable, ranging from 2.73 (MP2) to 3.15 A (HF). The value obtained by GED is 2.91(4) A, which could be confirmed by a scan of the potential-energy surface at the DF-LCCSD[T] level of theory. The nature of the weak dative bond in H(3)Si(CH(2))(3)NMe(2) can be described in terms of attractive inter-electronic correlation forces (dispersion) and is also interpreted in terms of the topology of the electron density.

A Theoretical Study of the Half-Sandwich Silicon(II) Cation [(Me5C5)Si]+ and of the Cationic Complex [(Me5C5)Si (DME)]+

“…Such effects are known to be overemphasized by MP2, but are described more balanced by SCS-MP2 [25] The situation in 2 is completely analogous to the bonding situation observed in N,N-dimethylaminopropylsilanes for the weak intramolecular Si-N interactions [26]. The main driving force for the complex formation can be assigned to electrostatic interactions.…”

London Dispersion in Molecular Chemistry—Reconsidering Steric Effects

“…[154] Open and cyclic conformers of N,N-dimethylaminopropylsilane (Scheme 4) were exhaustively characterized in the gas phase,i ns olution, and in the solid state. [156] In the crystalline state,t he molecule exists solely in the cyclic form with aw eak dative bond, while it displays ad ynamic equilibrium in the gas phase with at least three open conformers and ac yclic one.T he SiÀNb ond length (r), for which ab ond critical point was located, is 2.91 , as determined by gas-phase electron diffraction (GED). Computations at several levels of theory indicate that r Si-N crucially depends on the treatment of electron correlation and exhibits as catter from 3.14 ( HF) to 2.73 ( MP2).…”

The structure of tris(chloromethyl)amine in the gas phase using quantum chemical calculations and gas electron diffraction and as a solid and melt using Raman spectroscopy

“…On paper, TCMA shares structural similarities with tris(2-chloroethyl)amine, N(CH2CH2Cl)3, a powerful military-grade blister agent associated with acute cytotoxicity [31][32][33][34], but on the basis of the work by Oberhammer et al [18][19][20][21][22][23][24][25], the three-dimensional geometry around the amide centre should be anticipated to be quite different. Indeed, the structural solution in the gas phase from GED may be anticipated to be quite different to that obtained for the single crystal using XRD, as work by Mitzel et al [35][36][37][38][39] has demonstrated.…”