5-Chloro-3-[(E)-1,2-diphenylethenyl]-1H-indole

In the title compound, C22H16ClN, the pyrrole system makes a dihedral angle of 68.9 (1)° with the plane of phenyl ring at the ethenyl 1-position. An intramolecular C—H⋯π interaction is observed. In the crystal, intermolecular C—H⋯π interactions link the molecules into infinite chains running along the b axis.

In the title compound, C 22 H 16 ClN, the pyrrole system makes a dihedral angle of 68.9 (1) with the plane of phenyl ring at the ethenyl 1-position. An intramolecular C-HÁ Á Á interaction is observed. In the crystal, intermolecular C-HÁ Á Á interactions link the molecules into infinite chains running along the b axis. H atoms treated by a mixture of independent and constrained refinement Á max = 0.24 e Å À3 Á min = À0.23 e Å À3 Table 1 Hydrogen-bond geometry (Å , ).

Comment
Bhuvaneswari and co-workers (2007) investigated the reaction of indoles with alkynyl alcohols employing platinum as catalyst. Indium(III) bromide is known to catalyze intramolecular cyclization of 2-alkynylanilines (Sakai et al., 2008). The unique properties of indium halides and indium trifluoromethanesulfonate such as non-toxicity, stability in air, and water tolerance has also been described (Ghosh & Maiti 2007). Development of methodologies for heteroarene functionalization via C-H activation provides useful applications such as fluorescent dyes, synthetic analogues of natural products, and pharmaceuticals (Kakiuchi & Kochi, 2008). Against this background the structure of the title compound was determined by X-ray diffraction.
A perspective view of the title compound with the atom-numbering scheme is shown in Fig. 1. In the structure, all bond lengths and angles are within normal ranges (Allen et al., 1987). The chlorine atom deviates from the least squares planes of the C3-C8 benzene ring by 0.040 (1) Å. The dihedral angle between the pyrroline ring and phenyl ring (C10-C15) is 68.9 (1) °. The indole ring is planar as expected, the maximum deviation from the least squares plane being 0.034 (1) Å for atom C5. The dihedral angle between the phenyl rings C17-C22 and C24-C29 is 78.5 (2) °.
In the crystal structure two C-H···π interactions are observed. One intramolecular interaction determines the conformation of the molecules whereas one intermolecular interaction links the molecules to infinite chains. The C-H···π interactions involve rings C18-H18···Cg1 i (separation of 2.74 Å) and C20-H20···Cg2 ii (separation of 2.97 Å, Table 1, Cg1 is the centroid of the C10-C15 ring and Cg2 is the centroid of the C3-C8 ring).

Experimental
A mixture of diphenylacetylene (2.4 mmol), 5-Chloro indole (2 mmol) and indium tribromide (0.2 mmol) in toluene (4 ml) was stirred at 383 K for the appropriate time. After completion of the reaction as indicated by TLC, the reaction mixture was diluted with water and extracted with ethyl acetate. The combined organic layers were dried over anhydrous Na 2 SO 4 , concentrated in vacuo and purified by column chromatography on silica gel (Merck, 100 -200 mesh) to afford the desired product after crystallization (yield: 86%).

Refinement
All H atoms were positioned geometrically, with C-H = 0.93 Å and N-H = 0.84 Å. H atoms bonded to carbon were constrained to ride on their parent atoms, with U iso (H) = xU eq (C), where x = 1.5 for methyl H and x = 1.2 for all other H atoms. H1N was refined freely.