Crystal structures of three 4-substituted-2,2′-bipyridines synthesized by Sonogashira and Suzuki–Miyaura cross-coupling reactions

Abstract

Facile synthetic routes for three 4-substituted 2,2′-bipyridine derivatives, 4-[2-(4-methylphenyl)ethynyl]-2,2′-bipyridine, C19H14N2, (I), 4-[2-(pyridin-3-yl)ethynyl]-2,2′-bipyridine, C17H11N3, (II), and 4-(indol-4-yl)-2,2′-bipyridine, C18H13N3, (III), via Sonogashira and Suzuki–Miyaura cross-coupling reactions, respectively, are described. As indicated by X-ray analysis, the 2,2′-bipyridine core, the ethylene linkage and the substituents of (I) and (II) are almost planar [dihedral angles between the two ring systems: 8.98 (5) and 9.90 (6)° for the two molecules of (I) in the asymmetric unit and 2.66 (14)° for (II)], allowing π-conjugation. On the contrary, in (III), the indole substituent ring is rotated significantly out of the bipyridine plane [dihedral angle = 55.82 (3)°], due to steric hindrance. The crystal packings of (I) and (II) are dominated by π–π interactions, resulting in layers of molecules parallel to (30-2) in (I) and columns of molecules along the a axis in (II). The packing of (III) exhibits zigzag chains of molecules along the c axis interacting through N—H...N hydrogen bonds and π–π interactions. The contributions of unknown disordered solvent molecules to the diffraction intensities in (II) were removed with the SQUEEZE [Spek (2015). Acta Cryst. C71, 9–18] algorithm of PLATON. The given chemical formula and other crystal data do not take into account these solvent molecules.

Keywords

• crystal structure
• dye-sensitized solar cells
• 2,2′-bipyridine
• palladium-catalyzed
• Sonogashira cross-coupling
• Suzuki–Miyaura cross-coupling