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

• Published in: Chemistry : a European journal 2008-12, Vol.14 (35), p.11027-11038
• Main Authors: Hagemann, Michael, Berger, Raphael J. F., Hayes, Stuart A., Stammler, Hans‐Georg, Mitzel, Norbert W.
• Format: Article
• Language: English
• Subjects: ab initio calculations; conformation analysis; electron diffraction; IR spectroscopy; silanes
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200801273

N,N‐Dimethylaminopropylsilane H3Si(CH2)3NMe2 was synthesised by the reaction of (MeO)3Si(CH2)3NMe2 with lithium aluminium hydride. Its solid‐state structure was determined by X‐ray diffraction, which revealed a five‐membered ring with an Si⋅⋅⋅N distance of 2.712(2) Å. 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 Si⋅⋅⋅N 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 Si⋅⋅⋅N distance predicted by theory for the gas‐phase structure was highly variable, ranging from 2.73 (MP2) to 3.15 Å (HF). The value obtained by GED is 2.91(4) Å, 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 H3Si(CH2)3NMe2 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. Mia hamma des N,N‐Dimethylaminobrobilsilan ausm (MeO)3Si(CH2)3NMe2 und am Liziumaluminiumhidrid gmachd. Wenn ma des im fesdn Zuaschdand ois oanzeine Grisdalle durchleichd (OGD), kimds auf, das do Ringal vo jäweis fimbf Adome drinna hand, bei dene wo de Siliziumadome und de Schdigschdoffadome grod 2.712(2) Å ausananda hand. Ois a Gas, eleggdrona‐gschdraad (GES), IR schbeggdrosgobbisch undasuachd un ab‐initio un Dichtefunktional‐massig berächned, kimmd gee aussa, das do guadding drei andaschde Konformera, ois wia des oane mid de Ringal a no drinna hand. Am IR kend mas deswengn scho, das do de Ringal drinn hand, wei de symmädrischen und de ned‐symmädrischen Si–H Schdreggschwingunga um 200 Weinzoin ausanandagengand. Vo dem hea muas des a so sei, das do no a Schdiggschdoff an des Silizium hikoo