Crystal Structure of (E)-2-(3,3,3-trifluoroprop-1-en-1-yl)aniline

The molecule adopts an E configuration at the C=C double bond. The dihedral angle between the benzene ring and the prop-1-enyl group is 25.4 (3)°. In the crystal, molecules are linked via N—H⋯F hydrogen bonds, forming inversion dimers which are linked into ribbons along the b axis by C—H⋯N hydrogen bonds. The ribbons are linked by N—H⋯π and C—H⋯π interactions, generating a three-dimensional network.


Chemical context
Fluorescein, rhodamine etc. are water-soluble fluorescent reagents. Their derivatives exhibit strong fluorescence in aqueous solution and so can be utilized as ion-probes and in bio-imaging (Aron et al., 2016;Li et al., 2016). However, complicated procedures are required to obtain them. It is therefore desirable to develop a new fluorescent reagent with a simple structure that can be obtained by a short-step synthetic process. The title compound has a quite simple structure and is a small molecule, consisting of aniline and 3,3,3-trifluoroprop-1-enyl units, which emits strong fluorescence not only in organic solvents but also in an aqueous medium (H 2 O/DMSO, 90:10, v/v). Since aniline derivatives with 2,4-bis(3,3,3-trifluoroprop-1-enyl) have been used as fluorogenic substrates for dipepeptidyl peptidase-4 (Ogawa et al., 2017), the title compound can be treated as a simple but essential component in emitting fluorescence. Hence, it is important to study the relationship between the fluorescent properties and the molecular structure of the title compound. We report here its molecular and crystal structure.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The molecule adopts an E configuration with respect to ISSN 2056-9890 the C C double bond. The dihedral angle between the benzene ring and the prop-1-enyl group is 25.4 (3) . The C5-C10-C11-C12 and C9-C10-C11-C12 torsion angles are À158.9 (3) and 24.6 (4) , respectively. The bond lengths and angles in the title compound are normal and agree with those in other trifluoropropenylaniline compounds (Shimizu et al., 2009;Lin et al., 2014).

Supramolecular features
In the crystal, two molecules are associated through a pair of intermolecular N-HÁ Á ÁF hydrogen bonds (Table 1), forming a centrosymmetric dimer with an R 2 2 (16) ring motif (Fig. 2).
The dimers are further linked by C-HÁ Á ÁN hydrogen bonds (Table 1), forming a ribbon with a C(6) chain motif along the b-axis direction. The ribbons are linked by N-HÁ Á Á and C-HÁ Á Á interactions (Table 1), generating a three-dimensional network.  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A packing diagram of the title compound, viewed along the b axis. The N-HÁ Á ÁF and C-HÁ Á ÁN hydrogen bonds and N-HÁ Á Á and C-HÁ Á Á interactions are shown as dashed lines.

Figure 1
The molecular structure of the title compound with the atom-labelling scheme. Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.

Synthesis and crystallization
The title compound was prepared by a modification of a reported procedure (Omote et al., 2013). In a glove box purged with argon gas, iodoaniline (1.0 mmol), (2-methylallyl)palladium(II) chloride dimer (0.1mmol), CuF 2 (2.0 mmol) and 2,2 0 -bipyridyl (2.0 mmol) were placed in a flask. To the flask were added anhydrous DMF (6.0 ml) and (E)-trimethyl-(3,3,3-trifluoroprop-1-enyl)silane (2.0 mmol), and the mixture was stirred at 353 K. After the reaction mixture had been stirred for 4 h, it was poured into ice-water. The mixture was extracted with CH 2 Cl 2 , and the organic layer was dried over anhydrous MgSO 4 . After the solid had been filtered off, the solvent was removed in vacuo, and the residue was purified by silica gel column chromatography to give the product in 68% yield. Colourless single crystals were obtained by recrystallization from an ethyl acetate-hexane (1:10, v/v) solution (m.p.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The amino H atoms were located in a difference Fourier map and refined freely. The C-bound H atoms were positioned geometrically (C-H = 0.93-0.97 Å ) and refined using a riding model with U iso (H) = 1.2U eq (C). One outlier (511) was omitted in the last cycle of refinement.