title: Pentafluoroethyl-substituted α-silanes: model compounds for new insights.
abstract: To further investigate the α-effect in silanes bearing a geminal donor atom, the model compounds (C2F5)3SiCH2NMe2, (C2F5)3SiCH2OMe and (C2F5)3SiONMe2 were prepared by introduction of pentafluoroethyl groups via nucleophilic substitution of the corresponding chloro-derivatives with pentafluoroethyl lithium. The substances were characterised by NMR spectroscopy and X-ray diffraction via in situ crystallization techniques. The solid state structures of these highly electronegatively substituted α-silanes contain monomeric molecules. The Si-C-N angle in (C2F5)3SiCH2NMe2 shows a value of 115.3(2)° and the Si-C-O angle in (C2F5)3SiCH2OMe a value of 105.4(1)°. Both values are smaller than the Si-C-C angle of the reference compound (C2F5)3SiCH2CH3 with a value of 118.6(2)° indicating attractive interaction between the silicon atom and the respective donor atoms. The Si-O-N angle in (C2F5)3SiONMe2 is extremely narrow at 82.0(1)°. This behaviour was further investigated by gas electron diffraction and by quantum-chemical calculations. The NBO method finds no significant orbital interactions between Si and N/O atoms in the Si-C-N, Si-C-O and Si-O-N units. The IQA model describes the compounds as strongly stabilised by electrostatic interactions between formally non-bonded silicon and donor atoms.
authors.affiliation: Inorganic and Structural Chemistry, Centre for Molecular Materials CM2, Fakultät für Chemie, Universität Bielefeld, Universitätsstraße 25, 33615 Bielefeld, Germany. mitzel@uni-bielefeld.de.
authors.forename: Benedikt
authors.initials: B
authors.lastname: Waerder
authors.forename: Simon
authors.initials: S
authors.lastname: Steinhauer
authors.forename: Christian G
authors.initials: CG
authors.lastname: Reuter
authors.forename: Julia
authors.initials: J
authors.lastname: Bader
authors.forename: Beate
authors.initials: B
authors.lastname: Neumann
authors.forename: Hans-Georg
authors.initials: HG
authors.lastname: Stammler
authors.forename: Yury V
authors.initials: YV
authors.lastname: Vishnevskiy
authors.forename: Berthold
authors.initials: B
authors.lastname: Hoge
authors.forename: Norbert W
authors.initials: NW
authors.lastname: Mitzel