2-Bromo-5-tert-butyl-N-methyl-N-[2-(methylamino)phenyl]-3-(1-methyl-1H-benzimidazol-2-yl)benzamide

In the title compound, C27H29BrN4O, benzimidazole ring system and the amide moiety are planar [r.m.s. deviations = 0.016 (2) and 0.017 (1) Å, respectively]. The molecule adopts a conformation in which the amide linkage is almost perpendicular to the central ring [dihedral angle = 85.79 (8)°], while the benzimidazole ring system makes a dihedral angle of 70.26 (11)° with the central ring. In the crystal, the molecules form dimers through N—H⋯O hydrogen bonds and C—H⋯O interactions. These dimers are further linked into zigzag ribbons along [201] by weak C—H⋯Br interactions. As a result of the bulky nature of the molecule, as evidenced by the large dihedral angles between rings, there is little evidence for any π–π interactions.


Experimental
The methylation reaction of 2 ( Fig. 1) was carried out by reacting 1 (0.5 g, 1.12 mmol) with an excess of methyl iodide (1.75 g, 10 eq), followed by the addition of KOH (0.125 g, 2.24 mmol) in dry acetone (20 mL) and some molecular sieves. The reaction mixture was refluxed for 2 h. Then, it was diluted with ethyl acetate and washed with water. The organic layer was dried over Na 2 SO 4 and purified by column chromatography to afford 2 which was crystallized from a mixture of dichloromethane and ether. Anal. Calcd. for C 27 H 29 BrON 4 : C,64.16;H,5.78;N,11.08;found C,64.30;H,6.22;N,9.17.

Refinement
H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with a C-H distances of 0.95 and 0.98 Å U iso (H) = 1.2U eq (C) and 0.96 Å for CH 3 [U iso (H) = 1.5U eq (C)]. The hydrogen atom attached to N3 was located in a difference Fourier and refined isotropically.

Comment
The presence of imidazole rings in any molecular framework provides excellent modification sites for the fine tuning of properties related to electronic and steric factors. It has been reported in the literature that the strong electronic effect can be modified by the type of donor atoms and the electron-withdrawing and electron-releasing character of their substituents (Selander, & Szabó, 2011). Recently the effect of N-substitution on the catalytic activities of phosphinoimidazolines in palladium catalyzed Heck reactions has been reported (Busacca et al., 2003). Later, Reddy and co-workers (Reddy, & Krishna, 2005) have studied the use of bromine substituted benzimidazole in Heck reactions.
Pincer ligands have immense scope in exploring different types of metal coordination chemistry and stabilizing unusual species. They provide the sites which can be easily fine tuned to synthesize a number of metal complexes/species, which can be stabilized by three coordinating/bonding units of the pincer ligands. There are no examples of selenium containing benzimidazoles known in the literature. Therefore, 2, 2′-(2-bromo-5-(tert-butyl)-1,3-diyl)bis(1H-benzimidazole) (1) and its derivatives, having two coordinating imidazole rings were designed to incorporate selenium at 2-position of the phenyl group. An attempted methylation of 1 led to cleavage of the one of the benzimidazole rings and resulted in the formation of unexpected compound 2 (Fig. 1). 2-Bromo-5-(tert-butyl)isophthalic acid, the precursor for synthesizing 1, was prepared according to literature procedure (Field, et al., 2003). Compound 1 was synthesized by the reaction of 2bromo-5-tert-butyl-isophthalic acid with 1,2-phenylenediamine in polyphosphoric acid at 240°C.
In view of the above, the structure of the title compound, C 27 H 29 BrN 4 O, was determined (Fig. 2). The bond lengths and angles are all in the expected ranges (Allen et al., 1987) for such compounds. All the aromatic groups and the amide moiety are planar (rms deviations of 0.006 (1), 0.008 (2), 0.016 (2), and 0.017 (1) for the central phenyl ring, the supporting information sup-2 Acta Cryst. (2014). E70, o822-o823 substituent phenyl ring, the benzimidazole ring, and the amide moiety, respectively). The molecule adopts a conformation where the amide linkage is almost perpendicular to the central ring with a dihedral angle of 85.79 (8)° between central ring (C9-C14) and amide moiety (C19/C20/C21/N4/O1) while the benzimidazole ring makes a dihedral angle of 70.26° with the central ring. The molecules form dimers through N3-H···O1 intermolecular hydrogen bonds (Fig. 3). These dimers are further linked into zig-zag ribbons in the [2 0 1] direction by weak C-H···Br interactions. Because of the bulky nature of the molecule, as evidenced by the large dihedral angles between rings, there is little evidence for any π-π interactions.

Figure 1
The structures of 1 and 2.   Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Br 0.630352 (8)