Crystal structure of 3,5-bis(4-chlorophenyl)-1-propyl-1,3,5-triazacyclohexane

In the title molecule, C18H21Cl2N3, the triazacyclohexane ring adopts a chair conformation with both 4-chlorophenyl substituents in axial positions and the propyl group in an equatorial site. The dihedral angle between the planes of the benzene rings is 49.5 (1)°. In the crystal, molecules are arranged in a head-to-tail fashion, forming columns along [010], and pairs of weak C—H⋯π interactions form inversion dimers between columns.

Cg is centroid of C21-C26 ring. Crystal structure of 3,5-bis(4-chlorophenyl)-1-propyl-1,3,5-triazacyclohexane Leila Lefrada, Ahcene Bouchemma, Sofiane Bouacida, Nicolas Claiser and Mohamed Souhassou S1. Comment The conformational behaviour of substituted cyclohexanes as well as heterocyclohexanes has been the subject of numerous studies (Bushweller, 1995). The ring normally adopts the chair conformation unless specific intramolecular interactions stabilize the twist (Kleinpeter et al., 2005) or boat conformers (Freeman et al., 2005). Saturated sixmembered rings are prevalent in organic chemistry. For cyclohexane, experimental and computational studies have established that the chair conformation is 5.5 kcal/ mol more stable than the twist form (Wiberg et al., 1999). N,N′,N′′-Trisubstituted 1,3,5-triazinanes are of interest as precursors for the preparation of different N-substituted imidazoles (Mloston et al., 2006). The heterocyclic nucleus is expected to adopt a chair conformation and four distinct patterns of substituent orientation have to be considered, eee, eea, eaa and aaa, where e = equatorial and a = axial, with each of the conformers having axial repulsions involving the substituents or lone pairs of electrons on the N atoms. Several 1,3,5-trialkyl derivatives have been investigated in solution by dipole moment measurements and the results interpreted in terms of the eee conformer, the eea conformer (Baker et al., 1978), and varying amounts of the eee, eea and eaa conformers (Duke et al., 1973). Various 1,3,5-triaryl-1,3,5-triazacyclohexanes adopt the diaxial-equatorial orientation of substituents in the solid state thus avoiding 1,3-diaxial lone-pair repulsions (Giumanini et al. 1985;Gilardi et al. 2003Bouchemma et al. 19891990).
In the present work, a new derivate (I) of triazacyclohexane is reported and molecular structure is shown in Fig. 1. The 1,3,5-triazacycolohexane ring is in a chair conformation which is typical of this ring (Gilardi et al. 2003). The stucture of a similar compound viz 1-propyl-3-5-bis-(4-fluorophenyl)-1,3,5-triazacycolohexane (II) has been reported (Latreche et al. 2006). In both (I) and (II) the heterocyclic rings adopt chair conformations with two fluorophenyl substituents situated in axial positions and a third group (propyl) equatorial. The dihedral angle between the benzene rings (C11-C16/C21-C26) is 49.5 (1)°. In the crystal, molecules are arranged in a 'head to tail′ fashion forming columns along [010] (see Fig. 2) and pairs weak C-H···π interactions form inversion dimers between columns.

S2. Experimental
The title compound was obtained by mixing a 2:1:1 stoichiometric ratio of propylamine and 4-chloroaniline with formalin in ethanol (25 ml) at 293K. The resulting solution was evaporated on a rotary evaporator to dryness and the white residue was recrystallized from cyclohexane.

S3. Refinement
All non-H atoms were refined with anisotropic atomic displacement parameters. All H atoms were located in differnce Fourier maps but introduced in calculated positions and treated as riding on their parent C atom, with C-H distances of 0.93 Å (C aromatic ), 0.97 Å (C methylene ) and 0.96 Å (C methyl ) with U iso (H) = 1.2 U eq (C aromatic and C methylene ) or 1.5 U eq (C methyl ).

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. Part of the crystal structure of the title compound showing the 'head to tail′ arrangement of molecules arranged in columns.

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.