Crystal structure and Hirshfeld surface analysis of 4-allyl-6-bromo-2-(4-chlorophenyl)-4H-imidazo[4,5-b]pyridine

The imidazo[4,5-b]pyridine unit is planar, while the phenyl and allyl substituents are rotated a little out of this plane. In the crystal, molecules are linked via pairs of the weak intermolecular C—H⋯N hydrogen bonds, forming inversion dimers with (20) ring motifs. The dimers are further connected by π–π stacking interactions between the imidazo[4,5-b]pyridine ring systems.


Chemical context
Heterocyclic ring systems having an imidazo [4,5-b]pyridine unit can be considered as structural analogues of purines and have shown diverse biological activity depending on the substituents of the heterocyclic ring. Their activities include anticancer (Zhiqiang et al., 2005), tuberculostatic (Bukowski & Janowiec, 1989) and antimitotic (Parthiban et al., 2006) actions. Some imidazo [4,5-b]pyridine derivatives have also been reported as corrosion inhibitors for steel in acidic medium (Bouayad et al., 2018;Sikine et al., 2016), and some of them can be used to treat peptic ulcers, diabetes and mental illness (Scribner et al., 2007;Liang et al., 2007).
As a continuation of our research work devoted to the development of substituted imidazo[4,5-b]pyridine derivatives (Bourichi et al., 2016;Ouzidan et al., 2010a,b,c), we report herein the synthesis, the molecular and crystal structures along with the Hirshfeld surface analysis of the title compound, a new imidazo[4,5-b]pyridine derivative, which was obtained by the reaction of allyl bromide with 6-bromo-2-(4-chlorophen- ISSN 2056-9890 yl)-4H-imidazo [4,5-b]pyridine in the presence of a catalytic quantity of tetra-n-butylammonium bromide under mild conditions.

Figure 3
View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.1373 to 1.1294 a.u.

Figure 4
Hirshfeld surface of the title compound plotted over shape index.

Hirshfeld surface analysis
In order to visualize the intermolecular interactions in the crystal of the title compound, a Hirshfeld surface (HS) analysis (Spackman & Jayatilaka, 2009) was carried out using CrystalExplorer17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 3), the white surface indicates contacts with distances equal to the sum of the van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the sum of the van der Waals radii, respectively (Venkatesan et al., 2016). The bright-red spots appearing near atoms N1 and H15A indicate their roles as the respective donors and/or acceptors in the dominant C-HÁ Á ÁN hydrogen bond (Table 1) The full two-dimensional fingerprint plots for the title compound, showing (a) all contacts, and delineated into (b) HÁ Á ÁH, (c) HÁ Á ÁCl/ClÁ Á ÁH,
The residue was extracted with distilled water and the resulting mixture was chromatographed on a silica-gel column (eluent = ethyl acetate-hexane, 1:3 v/v). Brown single crystals suitable for X-ray diffraction were obtained by evaporation of an ethyl acetate-hexane (1:3 v/v) solution.

4-Allyl-6-bromo-2-(4-chlorophenyl)-4H-imidazo[4,5-b]pyridine
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.