3-(Diphenylmethylidene)indolin-2-one

The title molecule, C21H15NO, has an indoline-2-one and two benzene substituent groups which are arranged in a propeller-like fashion around the central C atom. The dihedral angle between the two benzene rings is 73.32 (16)° and those between the benzene rings and the indoline-2-one group are 76.54 (14) and 67.69 (14)°. In the crystal, there is an intermolecular N—H⋯O hydrogen-bonding interaction, which links the molecules into chains extending along c.

The title molecule, C 21 H 15 NO, has an indoline-2-one and two benzene substituent groups which are arranged in a propellerlike fashion around the central C atom. The dihedral angle between the two benzene rings is 73.32 (16) and those between the benzene rings and the indoline-2-one group are 76.54 (14) and 67.69 (14) . In the crystal, there is an intermolecular N-HÁ Á ÁO hydrogen-bonding interaction, which links the molecules into chains extending along c.

Related literature
For general background to indoline-2-one and its derivatives, see: Colgan et al. (1996). For the use of indoline-2-one as a precursor for the synthesis of organic luminescent molecules, see: Ji et al. (2010). For a related structure, see: Spencer et al.  Table 1 Hydrogen-bond geometry (Å , ).

Comment
Indoline-2-one and its derivatives are very important compounds as materials for the synthesis of pharmaceuticals (Colgan et al., 1996). Indoline-2-one may also be used as a precursor for synthesizing organic luminescent molecules because of its perfect conformation (Ji et al., 2010). In the course of exploring new electro-optic compounds, we obtained a intermediate compound C 21 H 15 NO (I) and the synthesis and structure are reported here.
The title compound has three substituent ring systems, an indoline-2-one ring and two benzene rings which are arranged in a propeller-like fashion around the central atom C9 (Fig. 1). The interplanar dihedral angle between the two benzene rings defined by C10-C15 and C16-C21 is 73.32 (16)°. The interplanar angles between these benzene planes and that of the indoline moiety are 76.54 (14)° and 67.69 (14)°, respectively. The molecules of (I) crystallize in the space group Pna2 1 which is different from that of 3-(propan-2-ylidene)indolin-2-one (P-1) (Spencer et al. 2010). In the crystal structure there is an intermolecular N-H···O hydrogen-bonding interaction (Table 1) linking the molecules into one-dimensional chains which extend along c in the unit cell (Fig. 2).

Experimental
Indolin-2-one (0.50 g, 3.76 mmol) was dissolved in THF (20 mL) and KOH (0.80 g, 14.3 mmol) was slowly added. After heating the stirred mixture at reflux temperature for 30 min, a solution of benzophenone (0.80 g, 4.40 mmol) in THF was slowly added and the refluxing continued for 2 h. The mixture was then cooled to 333 K and poured into water (200 mL) and was extracted with chloroform and dried over Na 2 SO 4 . After removing the solvent, the crude product was purified by column chromatography on silica gel, affording the title compound (yield: 0.28 g, 25%). The compound was then dissolved in THF and yellow crystals were formed on slow evaporation at room temperature over one week.

Refinement
All H atoms were placed in geometrically calculated positions and refined using a riding model with C-H = 0.93 Å and N-H = 0.86 Å and with U iso (H) = 1.2U eq (C, N). Friedel pairs (1153) were merged for the data used in the refinement.

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 > 2sigma(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.