(E)-1,2-Bis(1-propyl-5,6-dimethyl-1H-benzimidazol-2-yl)ethene

In the title compound, C26H32N4, the essentially planar (r.m.s. deviations of 0.0053 and 0.0242 Å) benzimidazole fragments are trans with respect to a central ethene fragment, and are canted in opposite directions by 2.78 (6) and 5.87 (6)° with respect to the ethene plane, giving the molecule a propeller conformation. The terminal ethyl fragments of the pendant n-propyl groups protrude to either side of the benzimidazole planes. Overall, the molecule exhibits a pseudo-center of symmetry at the mid-point of the ethene fragment. Both π–π stacking and typical C—H⋯π interactions are notably absent, as are intermolecular hydrogen bonds. When viewed along the a axis, the structure appears as criss-crossed layers of molecules with the planar fragments separated along the c-cell direction by the protruding ethyl groups.

In the title compound, C 26 H 32 N 4 , the essentially planar (r.m.s. deviations of 0.0053 and 0.0242 Å ) benzimidazole fragments are trans with respect to a central ethene fragment, and are canted in opposite directions by 2.78 (6) and 5.87 (6) with respect to the ethene plane, giving the molecule a propeller conformation. The terminal ethyl fragments of the pendant npropyl groups protrude to either side of the benzimidazole planes. Overall, the molecule exhibits a pseudo-center of symmetry at the mid-point of the ethene fragment. Bothstacking and typical C-HÁ Á Á interactions are notably absent, as are intermolecular hydrogen bonds. When viewed along the a axis, the structure appears as criss-crossed layers of molecules with the planar fragments separated along the ccell direction by the protruding ethyl groups.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: JH2128).

Comment
The title compound (I) was prepared as part of our long-term interest in the chemistry of bis(imidazoles), bis(benzimidazoles), and their complexes with metal ions. These species have demonstrated their usefulness as proton sponges (Stibrany et al., 2002), geometrically constraining ligands (Stibrany et al., 2004), agents to study electron transfer (Knapp et al., 1990), polymerization catalysts (Stibrany et al., 2003), and in the formation of metal-organic copolymers (Stibrany & Potenza, 2008), The present structure (Fig. 1) contains a central, planar trans 1,2-disubstituted ethene fragment linked at the 2 positions (C12 and C22) to 1-propyl, 5,6-dimethylbenzimidazole fragments. Excluding alkyl substituents, the structure can be viewed as three essentially planar fragments connected by two hinges, the C1-C12 and C2-C22 bonds. The benzimidazole fragments are canted in opposite directions by 2.78 (6)° (bzim 1) and 5.87 (6)°(bzim2) to give the molecule a slight propeller-like shape, while the ethyl fragments of the pendant n-propyl groups, which protrude above and below the planes of the benzimidazole fragments, help to ensure that the molecule has an approximate center of symmetry at the midpoint of the C1-C2 bond.
When viewed approximately along the a cell direction (Fig.2), the structure appears as layers of criss-crossed molecules with the planar fragments separated along the c cell direction by the protruding ethyl groups. A comparative view along the b cell direction (Fig. 3) shows the protruding ethyl groups in a different orientation and indicates clearly the lack of coplanarity of the benzimidazole fragments. These figures are consistent with the absence of π-π stacking and typical C-H···π interactions found by Platon (Spek, 2009). The absences noted above are consistent with the ethyl group conformations, which appear to prevent effective overlap of the π systems. The lack of intermolecular hydrogen bonds is also attributed to the n-propyl substituents, which prevent the formation of intermolecular N(imine)··· H-N(amine) hydrogen bonds.
After a reaction time of 10 minutes, n-propyl iodide (2 molar equivalents) was added dropwise. After an additional hour, the product was precipitated with water, collected by filtration, and dried in air. Crystals of (I) (m.p. 523 (soften) 538-539 K(melt)) were obtained by slow cooling of a hot DMSO solution of (I). is remarkably less soluble in a variety of solvents than analogous bis(benzimidazole)ethene compounds previously reported (Stibrany et al., 2005;Stibrany & Potenza, 2006a,b;Stibrany & Potenza, 2009) which, in contrast to (I), were not substituted at the 5 and 6 positions.
supplementary materials sup-2 Refinement Hydrogen atoms were positioned geometrically using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2 U eq (C).

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.
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 Rfactors(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.