3,4-Dinitro-2,5-bis[4-(trifluoromethyl)phenyl]thiophene

The title compound, C18H8F6N2O4S, is a precursor for the production of low-band-gap conjugated polymers. In the crystal structure, the dihedral angles between the thiophene and benzene rings are 35.90 (8) and 61.94 (8)°, and that between the two benzene rings is 40.18 (8)°. The two nitro groups are twisted with respect to the thiophene ring, the dihedral angles being 53.66 (10) and 31.63 (10)°. Weak intermolecular C—H⋯O hydrogen bonding helps to stabilize the crystal structure.


3,4-Dinitro-2,5-bis[4-(trifluoromethyl)phenyl]thiophene
Ping-Hsin Huang, Jiun-Yi Shen and Yuh-Sheng Wen S1. Comment The title compound, (I), has been shown to be an excellent precursor for the production of low band gap conjugated polymers and organic light-emitting devices etc. As indicated in Scheme 2, standard procedures were administrated to synthesize in high yield. The molecular structure is shown in Fig. 1. The double bonds and C-C single bond of (I) are slightly shorter than those of the parent thiophene, while the S-C single bond is slightly elongated (Bak et al., 1961).

S2. Experimental
The compound was synthesized by the following procedure. A two-necked round-bottomed flask was charged with Pd(PPh 3 ) 4 (280 mg), tributyl(4-(trifluoromethyl)phenyl)stannane (3.26 g, 7.5 mmol), 2,5-dibromo-3,4-dinitrothiophene (1.00 g, 3.0 mmol) and DMF (20 ml), and the reaction mixture stirred under nitrogen and heated at 343 K for 48 h. After cooling, the mixture was diluted with diethyl ether and the organic phase was washed with water and brine. After drying over anhydrous MgSO 4 and removing the volatiles, the residue was purified by column chromatography using CH 2 Cl 2 /nhexane as eluent, followed by recrystallization from CH 2 Cl 2 and hexane to yield 0.7 g (50%) of (I) as a white solid.
Crystals suitable for X-ray diffraction were grown from a CH 2 Cl 2 solution layered with hexane at room temperature.

S3. Refinement
H atoms were located geometrically and treated as riding atoms, with C-H = 0.93 Å, and with U iso (H) = 1.2U eq (C).  A molecular structure of (I) with 30% probability displacement ellipsoids, showing the atom-numbering scheme employed. H atoms are shown as small spheres of the arbitrary radii.

Figure 2
The formation of the title compound.  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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S 0.49028 (6)