N-(2,6-Diisopropylphenyl)formamide toluene 0.33-solvate

The crystal packing of the title compound, C13H19NO·0.33C7H8, shows a channel at [001], which contains grossly disordered toluene solvent molecules. The angle between the benzene ring and the mean plane of the formamide group is 71.1 (1)°. The amide groups of neighbouring molecules are connected by N—H⋯O hydrogen bonds, forming 21 helical chains propagating along [001]. Molecules are also connected by weak intermolecular C—H⋯O hydrogen bonds, forming 61 helices.


Comment
The title compound was obtained as a byproduct from the synthesis of the N-heterocyclic carbene precursor 1,3-bis-(2,6diisopropylphenyl)imidazolium chloride (Hintermann, 2007). Crystallization from a solution in toluene provided single crystals of the title compound, whose crystal structure is reported herein.
The molecular structure of the title molecule is shown in Fig. 1. The angle between the benzene ring and the mean plane of the formamide group is 71.1 (1)°. It is slightly smaller than the value of 77.4 (1)° reported for the crystal structure of the solvent-free compound (Stibrany & Potenza, 2006;Chitanda et al., 2008). This non-planar geometry is required by steric repulsions between the formamide group and the isopropyl substituents. An almost planar molecule has been reported for non-substituted N-phenylformamide (Omondi et al., 2008;Gowda et al., 2009).
In the crystal, molecules are connected by intermolecular hydrogen bonding between the amide groups to form helical 2 1 chains in the c axis direction (Table1, Fig. 2). The molecules are also connected by a weak intermolecular formamidebenzene C-H···π interaction. The C-H vector of this contact does not point to the midpoint of the acceptor ring, but points more closely to the C3-C4 bond. Similar hydrogen bonded chains occur in the solvent-free compound mentioned above. Molecules in adjacent chains are connected by a very weak intermolecular benzene-formamide C-H···O interaction to form a helix about a 6 1 screw axis.
The crystal packing (Fig. 3) shows a channel along the c axis with an average radius of 3.71 Å and it is surrounded by isopropyl groups. Each channel contains two toluene solvate molecules per unit cell, as estimated by the SQUEEZE routine in PLATON (Spek, 2009).
Crystallization from toluene resulted in the formation of colourless rod-shaped crystals of the title compound. To confirm the toluene contents of the sample, some single crystals were dissolved in CDCl 3 . 1 H-NMR spectra of this solution showed the resonances of the major and minor rotamer of N-(2,6-diisopropylphenyl)formamide (Chitanda et al., 2008) and also the resonances of toluene. toluene molecules in the unit cell. The NH H atom was located in a difference electron-density map and freely refined.

Refinement
The C-bound H atoms were included in calculated positions and treated as riding atoms: C-H = 0.95, 0.98 and 1.00Å for CH(aromatic), CH 3 and CH(methine) H atoms, respectively, with U iso (H) = k × U eq (parent C-atom), where k = 1.5 for CH 3 H-atoms and = 1.2 for other H-atoms.

Figure 1
The molecular structure of the title molecule, showing the atom-labelling. Displacement ellipsoids are drawn at the 50% probability level.

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.