Synthesis and comparative structural study of 2-(pyridin-2-yl)-1 H-perimidine and its mono- and di- N-methyl-ated analogues

Abstract

The title compounds, 2-(pyridin-2-yl)-1H-perimidine (C₁₆H₁₁N₃; 1), 1-methyl-2-(pyridin-2-yl)-1H-perimidine (C₁₇H₁₃N₃; 2), and 1,3-dimethyl-2-(pyridin-2-yl)-1H-perimidinium iodide (C₁₈H₁₆N₃ ⁺·I^-; 3) were synthesized under mild conditions and their structures were determined by ¹H NMR spectroscopy and single-crystal X-ray analysis. The N-methyl-ation of the nitro-gen atom(s) at the perimidine moiety results in a significant increase of the inter-plane angle between the pyridin-2-yl ring and the perimidine system. The unsubstituted perimidine (1) forms a weak intra-molecular N-H⋯N bond that consolidates the mol-ecular conformation. In the crystal structures of 1-3, the mol-ecular entities all are assembled through π-π and C-H⋯π inter-actions.

Keywords: NMR study; crystal structure; hydrogen-bonding; perimidine; π–π stacking.