2-(1,3-Dibenzylimidazolidin-2-ylidene)malononitrile

In the title molecule, C20H18N4, the imidazolidine ring makes dihedral angles of 86.74 (2) and 81.18 (3)° with the two phenyl rings. In the absence of classical intermolecular interactions, the crystal packing is stabilized by van der Waals forces.


Related literature
For the crystal structures of related compounds, see: Adhikesavalu & Venkatesan (1982). For details of the biological activities of imidazolidine-containing compounds, see: Sasho et al., 1994. For bond-length data, see: Allen et al. (1987.

S1. Comment
Imidazolidine is an important group in organic chemistry. Many compounds containing imidazolidine groups possess a broad spectrum of biological activities (Sasho et al., 1994). Here, we report the crystal structure of (I).

S2. Experimental
A solution of 2-(imidazolidin-2-ylidene)malononitrile 1.34 g (10 mmol) and sodium hydride 0.3 g dissolved in anhydrous acetonitrile (20 ml), and dropwise added over a period of 10 min to a solution of 1-(chloromethyl)benzene 2.53 (20 mmol) in acetonitrile (10 ml) at 273 K. The mixture was stirred at 353 K for 3 h. The solvent was removed and the residue was purified by flash chromatography (1:1 cyclohexane:dichloromethane) to give I as a white solid (2.67 g, 85%).
Single crystals suitable for X-ray measurements were obtained by recrystallization from ethanol at room temperature.

S3. Refinement
H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 or 0.97 Å, with U iso (H) = 1.2 times U eq (C). In the absence of significant anomalous scattering effects, Friedel pairs were merged.

Figure 1
The molecular structure of (I), with atom labels and 40% probability displacement ellipsoids for non-H atoms.

Special details
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.