Synthesis and crystal structures of N,2,4,6-tetramethylanilinium trifluoromethanesulfonate and N-isopropylidene-N,2,4,6-tetramethylanilinium trifluoromethanesulfonate

Abstract

Two 2,4,6-trimethylaniline-based trifuloromethanesulfonate (trifluoromethanesulfonate) salts were synthesized and characterized by single-crystal X-ray diffraction. N,2,4,6-Tetramethylanilinium trifluoromethanesulfonate, [C10H14NH2+][CF3O3S−] (1), was synthesized via methylation of 2,4,6-trimethylaniline. N-Isopropylidene-N,2,4,6-tetramethylanilinium trifluoromethanesulfonate, [C13H20N+][CF3O3S−] (2), was synthesized in a two-step reaction where the imine, N-isopropylidene-2,4,6-trimethylaniline, was first prepared via a dehydration reaction to form the Schiff base, followed by methylation using methyl trifluoromethanesulfonate to form the iminium ion. In compound 1, both hydrogen bonding and π–π interactions form the main intermolecular interactions. The primary interaction is a strong N—H...O hydrogen bond with the oxygen atoms of the trifluoromethanesulfonate anions bonded to the hydrogen atoms of the ammonium nitrogen atom to generate a one-dimensional chain. The [C10H14NH2+] cations form dimers where the benzene rings form a π–π interaction with a parallel-displaced geometry. The separation distance between the calculated centroids of the benzene rings is 3.9129 (8) Å, and the interplanar spacing and ring slippage between the dimers are 3.5156 (5) and 1.718 Å, respectively. For 2, the [C13H20N+] cations also form dimers as in 1, but with the benzene rings highly slipped. The distance between the calculated centroids of the benzene rings is 4.8937 (8) Å, and interplanar spacing and ring slippage are 3.3646 (5) and 3.553 Å, respectively. The major intermolecular interactions in 2 are instead a series of weaker C—H...O hydrogen bonds [C...O distances of 3.1723 (17), 3.3789 (18), and 3.3789 (18) Å], an interaction virtually absent in the structure of 1. Fluorine atoms are not involved in strong directional interactions in either structure.

Keywords

• crystal structure
• iminium ion
• ammonium ion
• trifluoromethanesulfonate
• trifluoromethanesulfonate
• 2–4,6-trimethylaniline
• methylation
• n,2,4,6-tetramethylanilinium
• n-isopropylidene-n,2,4,6-tetramethylanilinium