Synthesis and crystal structures of N,2,4,6-tetra-methyl-anilinium tri-fluoro-methane-sulfonate and N-iso-propyl-idene- N,2,4,6-tetra-methyl-anilinium tri-fluoro-methane-sulfonate

Abstract

Two 2,4,6-tri-methyl-aniline-based trifuloro-methane-sulfonate (tri-fluoro-methane-sulfonate) salts were synthesized and characterized by single-crystal X-ray diffraction. N,2,4,6-Tetra-methyl-anilinium tri-fluoro-methane-sulfonate, [C₁₀H₁₄NH₂ ⁺][CF₃O₃S^-] (1), was synthesized via methyl-ation of 2,4,6-tri-methyl-aniline. N-Iso-propyl-idene-N,2,4,6-tetra-methyl-anilinium tri-fluoro-meth-ane-sulfonate, [C₁₃H₂₀N⁺][CF₃O₃S^-] (2), was synthesized in a two-step reaction where the imine, N-iso-propyl-idene-2,4,6-tri-methyl-aniline, was first prepared via a dehydration reaction to form the Schiff base, followed by methyl-ation using methyl tri-fluoro-methane-sulfonate to form the iminium ion. In compound 1, both hydrogen bonding and π-π inter-actions form the main inter-molecular inter-actions. The primary inter-action is a strong N-H⋯O hydrogen bond with the oxygen atoms of the tri-fluoro-methane-sulfonate anions bonded to the hydrogen atoms of the ammonium nitro-gen atom to generate a one-dimensional chain. The [C₁₀H₁₄NH₂ ⁺] cations form dimers where the benzene rings form a π-π inter-action with a parallel-displaced geometry. The separation distance between the calculated centroids of the benzene rings is 3.9129 (8) Å, and the inter-planar 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 inter-planar spacing and ring slippage are 3.3646 (5) and 3.553 Å, respectively. The major inter-molecular inter-actions 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 inter-action virtually absent in the structure of 1. Fluorine atoms are not involved in strong directional inter-actions in either structure.

Keywords: 2–4,6-tri­methyl­aniline; N,2,4,6-tetra­methyl­anilinium; N-iso­propyl­idene-N,2,4,6-tetra­methyl­anilinium; ammonium ion; crystal structure; iminium ion; methyl­ation; tri­fluoro­methane­sulfonate.