Synthesis and Structure of Methylated Acetylenic Nitriles

Cyanoacetylene and dicyanoacetylene react in the ternary methylation system CH₃F/SbF₅/SO₂ under the formation of its corresponding N-monomethylated and N,N′-dimethylated species, respectively. Additionally, in the case of dicyanoacetylene, an N,N′-dimethylated HF-addition product was obtained. The salts were characterized by low-temperature vibrational spectroscopy. In the case of [C₄H₄N][SbF₆], [C₅H₃N₂][SbF₆]·SO₂, and [C₆H₈N₂F₂][SbF₆]₂, single-crystal X-ray structures are reported. Surprisingly, all of the obtained salts are room-temperature stable. The experimental data are discussed, together with quantum chemical calculations at the M06-2X/aug-cc-pVTZ level of theory.