Zwitterionic lambda Si-5-organofluorosilicates of the formula types F(4)SiCH(2)NMe(2)R and F(3)MeSiCH(2)NMe(2)R (R=H, Me) and related compounds: Synthesis, structure, and dynamic behavior

The zwitterionic lambda(5)Si-organofluorosilicates F(4)SiCH(2)NMe(2)H (5) and F(3)MeSiCH(2)NMe(2)H (7; crystallographic modifications 7a and 7b) were synthesized by reaction of the silanes (MeO)(3)SiCH(2)NMe(2) (11) and (MeO)(2)MeSiCH(2)NMe(2) (13), respectively, with HF in a mixture of ethanol and hydrofluoric acid at 0 degrees C. The related zwitterionic lambda(5)Si-organofluorosilicates F(4)SiCH(2)NMe(3) (6) and F(3)MeSiCH(2)NMe(3) (8) were obtained analogously by reaction of HF with the ammonium iodides [(MeO)(3)SiCH(2)NMe(3)]I (12) and [(MeO)(2)MeSiCH(2)NMe(3)]I (14), respectively. Reaction of the silanes (MeO)(3)SiCH(2)NR(2) (16) and (MeO)(2)(t)BuSiCH(2)NR(2) (17) (NR(2) = 2,2,6,6-tetramethylpiperidino) with HF gave the zwitterionic lambda(5)Si-organofluorosilicates F(4)SiCH(2)NR(2)H (9) and F(3)(t)BuSiCH(2)NR(2)H (10), respectively. The crystal structures of compounds 5, 6, 7a,b, and 8-10 were determined by single-crystal X-ray diffraction studies. Compounds 5-10 were studied by solution-state H-1, C-13, F-19, and Si-29 NMR experiments at room temperature (solvent CD3CN). These studies indicate a rapid fluorine exchange at room temperature. As shown by temperature-dependent F-19 NMR experiments with 10 (solvent CD2Cl2), this ligand exchange can be reduced on cooling. According to lineshape analyses, the dynamic behavior of 10 can be described by two different; processes. For compounds 5-8 and related model species ab initio studies at the SCF/SVP and MP2/TZP levels were performed. Calculated and experimental (crystal structures) geometric data were compared, and the influence of intermolecular interactions (packing effects) in the solid state and intramolecular interactions between the charged centers in the calculated zwitterions were studied. Furthermore, the dynamic behavior of the title compounds was investigated by ab initio studies of the related model species F4SiCH2NH3 (19) and F(3)MeSiCH(2)NH(3) (20).