1,3-Bis(pyridin-2-yl)-1H-benzimidazol-3-ium tetrafluoridoborate

The asymmetric unit of the title compound, C17H13N4 +·BF4 −, contains one half of the benzimidazolium cation and one half of the tetrafluoridoborate anion, with crystallographic mirror planes bisecting the molecules. One F atom of the tetrafluoridoborate is equally disordered about a crystallographic mirror plane. In the crystal, C—H⋯F interactions link the cations and anions into layers parallel to (100). The crystal packing is further stabilized by F⋯π contacts involving the tetrafluoridoborate anions and the five-membered rings [F⋯centroid = 2.811 (2) Å].

The asymmetric unit of the title compound, C 17 H 13 N 4 + ÁBF 4 À , contains one half of the benzimidazolium cation and one half of the tetrafluoridoborate anion, with crystallographic mirror planes bisecting the molecules. One F atom of the tetrafluoridoborate is equally disordered about a crystallographic mirror plane. In the crystal, C-HÁ Á ÁF interactions link the cations and anions into layers parallel to (100). The crystal packing is further stabilized by FÁ Á Á contacts involving the tetrafluoridoborate anions and the five-membered rings [FÁ Á Ácentroid = 2.811 (2) Å ].
We used the N,N'-bis(2-pyridyl)-benzene-1,2-diamine compound as a starting material for the synthesis of the title compound, a new imidazolium salt. Despite the fact that the synthesis of the starting material N,N'-bis(pyridin-2-yl)benzene-1,2-diamine had been reported previously (Gdaniec et al., 2004), we optimized the procedure to obtain a better yield (91 instead of 70%) using the reaction reported in the Experimental section ( Fig. 4) with a microwave technique. A similar procedure was succesfully used to synthesize the title compound in a very high yield (99.7%). It is the first example of a coupling between a halo pyridine and an aniline made with microwave heating that does not imply the use of any metal.
This method to couple halo pyridines and anilines can be very useful to produce compounds with pharmaceutical activity since many pharmaceuticals are based on the aniline-pyridine scaffold (Kim et al., 1996;Wu et al., 2001).
The asymmetric unit of the title compound, C 17 H 13 N 4 + .BF 4 -, contains one half-molecule of the benzimidazolium cation and one half-molecule of the anion, crystallographic mirror planes bisecting the molecules (Fig. 1). One F atom of the tetrafluoroborate is disordered over two positions. The second position being generated by a crystallographic mirror plane, the site-occupancy factor is 0.5. The benzimidazole and pyridine rings are not coplanar, the dihedral angle between the mean planes is 26.67 (4)°.

Experimental
To benzene-1,2-diamine (2.7 g, 24.97 mmol) in a microwave vial, 2-chloropyridine (9 ml, 46.95 mmol) was added. The vial was then closed with a cap consisting of a Teflon septum and the reaction mixture was heated for 35 mins at 458 K. Monitoring with TLC (thin layer chromatography) and GC-MS (gas chromatography -mass spectrometry) showed that the benzene-1,2-diamine was consumed after this time and the mixture was allowed to cool to room temperature. The crude mixture was dissolved in water (15 ml) and dropped into a solution of concentrated ammonia in water (25 ml of NH 4 OH 24.5% in 250 ml of water). The resulting pink-red precipitate was filtered off, washed with water (50 ml) and was subsequently dried in air to give N,N'-bis(pyridin-2-yl)benzene-1,2-diamine. Further recrystallization from ethanol gave a very pure product (yield: 2.902 g, 91%).
supplementary materials sup-2 To N,N'-bis(pyridin-2-yl)benzene-1,2-diamine (500 mg, 1.91 mmol) in a microwave vial, finely ground ammonium tetrafluoroborate (204 mg, 1.91 mmol) was added followed by the triethyl orthoformate (10 ml, 59 mmol). The vial with the red pink suspension was then closed with a cap consisting of a Teflon septum and the reaction mixture was heated for 25 minutes at 413 K and then for further 20 minutes to 433 K. After that time inside the vial a blue-violet solid was present and TLC analysis showed that the starting material had been consumed. The solid was separated off and then stirred with ethyl acetate (3x50 ml) for 15 minutes. It was then collected by suction filtration, washed with diethyl ether and dried to afford a deep violet-blue compound (yield: 686 mg, 99.7%). Recrystallization from a hot saturated solution of water/methanol (9/2) afforded red plate-like crystals of the title compound, suitable for X-ray analysis. Spectroscopic data for the title compound are given in the archived CIF.

Refinement
One F atom of the tetrafluoroborate ion is disordered over two positions around a mirror plane (site-occupancy factor of 1/2). H-atom H1 was located in a difference Fourier map and was freely refined. The C-bound H-atoms were included in calculated positions and treated as riding atoms: C-H = 0.93 Å with U iso (H) = 1.2U eq (C). Fig. 1. The molecular structure of the title compound, with the numbering scheme and displacement ellipsoids drawn at the 50% probability level (H-atoms are shown as spheres of arbitrary size). Symmetry code: (i) -x + 3/2, -y, z -1/2.  Table 1 for details).   95, 141.60, 129.49, 126.93, 118.83, 118.26,116.86. 19 F-NMR in CD 3 CN: δ = -152.32.

Figures
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 mat-  (17)