Crystal Structure Analysis and NMR Spectra of N-(Pentafluorobenzoyl)-4-dimethylaminopyridinium Hexachloroantimonate(V)

The crystal structure analysis of N-(pentafluorobenzoyl)-4-dimethyl- aminopyridinium hexachloroantimonate(V) (space group: PI, measurement at -80 °C; high-order refinement; R = 0.035, Pw = 0.035 with all data) shows, that the carbonyl group and the dimethylaminopyridine (DMAP) fragment have a practically coplanar arrangement, while the pentafluorophenyl group is twisted b yea. 69° out of that plane. The resulting CO-DMAP-TT-interaction allows a charge delocalization towards the dimethylamino group, i.e. the cation may be best described as an iminium ion. The crystal packing reveals cation-anion interactions only in the formal iminium fragment. The carbonyl-C atom, which is attacked by a nucleophile in the course of an acylation reaction, has two intramolecular and one intermolecular van der Waals contacts to fluorine atoms. The structure is also interpreted in terms of a beginning dissociation into an acyl cation and DMAP. The \u27H, 13C and 19F NMR spectra are compared with those of related molecules