Isotypic crystal structures of 2,6-dibromo-N,N-bis(4-nitrophenyl)aniline and 2,6-dichloro-N,N-bis(4-nitrophenyl)aniline

The central ternary N atoms in the isotypic crystal structures of the substituted anilines show no sign of pyramidalization.


Chemical context
Arylamines are among the most important electron donors for functional organic materials, e.g. organic light emitting diodes (OLEDs) (Shirota & Kageyama, 2007;Tao et al., 2011;Yook & Lee, 2012). In particular, triphenylamine-based compounds have received great attention due to their good hole-transport properties. Substituted triphenylamines are therefore highly desirable for further chemical modification, for example, cross-coupling or C-H activation.
We have investigated the conversion of 2,6-dihalogenated anilines (X = Cl, Br) with 1-fluoro-4-nitrobenzene. Despite the sterical demand of the halogen substituents, no diphenylamine intermediates were obtained whereas the title tetra-substituted triphenylamines (I) and (II) could be isolated and their crystal structures are reported here. atoms in both structures show no pyramidalization, with only marginal displacements from the planes of the bonded C atoms (C1/C7/C13) of 0.0058 (13) Å for (I) and of 0.0074 (9) Å for (II).
The nitro groups are twisted slightly out of the plane of the benzene ring to which they are attached with dihedral angles of 8.29 (19)

Supramolecular features
The crystal packing of the structures of both (I) and (II) is consolidated by weak -C-HÁ Á ÁO-N interactions (Tables 1  and 2) and XÁ Á ÁO contacts that are shorter than the sum of the van der Waals radii (Bondi, 1964) of the respective elements. For (I) the BrÁ Á ÁO contact is 3.3557 (13) Å , and for (II) the ClÁ Á ÁO contact is 3.2727 (9) Å . Both types of intermolecular interactions lead to the formation of a three-dimensional network (Fig. 2).

Database survey
A search of the Cambridge Structural Database (Version 5.35, last update February 2014;Allen, 2002) indicated the presence of 759 molecules containing a triphenylamine backbone or of their metal-organic derivatives; they exclude, however, ringclosed systems such as N-phenylcarbazoles or N-phenylphenothiazines. None of these 759 molecules possesses the substitution pattern of the title compounds, viz. two para-and one ortho,ortho-substituted benzenes with respect to the N atom. The crystal structures of one para-nitro-substituted triphenylamine, viz. tris-(4-nitrophenyl)amine (Welch et al., 2005) and one ortho,ortho-dichloro-substituted triphenylamine, viz. tris-(2,3,4,5,6-pentachlorophenyl)amine (Hayes et al., 1980) have been reported. As in the title compounds, in both of these molecules the N atom is virtually coplanar with the three connecting C atoms. In the crystal structure of unsubstituted triphenylamine (Sobolev et al., 1985), on the other hand, in three out of four molecules, the N atom is located distinctly out of the plane defined by the connecting C atoms.

Figure 2
A view of the crystal packing of compound ( obtained after column chromatography (light petroleum: EtOAc 7:3) as a yellow solid (374 mg, 0.93 mmol, 74%). Yellow single crystals were grown from a CDCl 3 solution by slow evaporation of the solvent. Spectroscopic data for compound (I) are available in the archived CIF. Compound (II) was prepared by heating 2,6-dibromoaniline (627 mg, 2.50 mmol, 1.0 eq.), 1-fluoro-4-nitrobenzene (353 mg, 2.50 mmol, 1.0 eq.) and Cs 2 CO 3 (896 mg, 2.75 mmol, 1.1 eq.) in DMSO (5 ml) at 413 K for 18 h in a capped vial using a heating block. After cooling, the reaction mixture was poured into water and the aqueous phase was extracted with CH 2 Cl 2 . The combined organic phases were dried over anhydrous Na 2 SO 4 and concentrated under reduced pressure. Compound (II) was obtained after crystallization from an EtOH/toluene mixture as a brown solid (237 mg, 0.48 mmol, 38%). Yellow single crystals were grown from a CDCl 3 solution by slow evaporation of the solvent. Spectroscopic data for compound (II) are available in the archived CIF.

Refinement
The hydrogen atoms in both structures, (I) and (II), were clearly discernible from difference Fourier maps and were refined as riding with C-H = 0.96 Å and U iso (H) = 1.2U eq (C). Experimental details are given in Table 3.