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(Dimethylaminomethyl)trifluorosilane, Me 2 NCH 2 SiF 3 —A Model for the α‐Effect in Aminomethylsilanes
Author(s) -
Mitzel Norbert W.,
Vojinović Krunoslav,
Foerster Thomas,
Robertson Heather E.,
Borisenko Konstantin B.,
Rankin David W. H.
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500359
Subject(s) - crystallography , chemistry , dimer , adduct , molecule , crystal structure , electron diffraction , spectroscopy , ab initio quantum chemistry methods , crystal (programming language) , ab initio , diffraction , physics , organic chemistry , programming language , quantum mechanics , computer science , optics
F 3 SiCH 2 NMe 2 was prepared as a model for the investigation of the nature of the α‐effect in α‐aminosilanes, by fluorination of Cl 3 SiCH 2 NMe 2 with SbF 3 . Under less mild conditions SiC bond cleavage was also observed, leading to the double adduct F 4 Si(Me 2 NCH 2 SiF 3 ) 2 , which was characterised by a crystal structure analysis showing that the central SiF 4 unit is connected to Me 2 NCH 2 SiF 3 via Si⋅⋅⋅N dative bonds and F⋅⋅⋅Si contacts. F 3 SiCH 2 NMe 2 was characterised by multinuclear NMR spectroscopy ( 1 H, 13 C, 15 N, 19 F and 29 Si), gas‐phase IR spectroscopy and mass spectrometry. It is a dimer in the crystal (X‐ray diffraction, crystal grown in situ), held together by two SiN dative bonds. In solution and in the gas phase the compound is monomeric. The structure of the free molecule, determined by gas‐phase electron diffraction, showed that, in contrast to former postulates, there are no attractive Si⋅⋅⋅N interactions. Ab initio calculations have been carried out to explain the nature of the bonding. F 3 SiCH 2 NMe 2 has an extremely flat bending potential for the Si‐C‐N angle; the high degree of charge transfer from the Si to the N atoms which occurs upon closing the Si‐C‐N angle is in the opposite direction to that expected for a dative bond. The topology of the electron density of F 3 SiCH 2 NMe 2 was analysed. Solvent simulation calculations have shown virtually no structural dependence on the medium surrounding the molecule. The earlier postulate of Si→N dative bonds in SiCN systems is discussed critically in light of the new results.