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

Gabriele Grieco; Olivier Blacque; Heinz Berke

doi:10.1107/S1600536811027942

. 2011 Jul 16;67(Pt 8):o2066–o2067. doi: 10.1107/S1600536811027942

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

Gabriele Grieco ^a, Olivier Blacque ^a,^*, Heinz Berke ^a

PMCID: PMC3213512 PMID: 22091091

Abstract

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].

Related literature

For applications of N,N′-bis(2-pyridyl)aryldiamines, see: Stoessel et al. (2010 ▶); Goldfarb (2009 ▶) and of imidazolium salts, see: Berlin et al. (2007 ▶); Bold et al. (2005 ▶); Huang et al. (2005 ▶); Murakami et al. (2007 ▶); Teles et al. (1996 ▶). For pharmaceuticals based on the aniline–pyridine scaffold, see: Kim et al. (1996 ▶); Wu et al. (2001 ▶). For the synthesis of the starting material N,N′-bis(pyridin-2-yl)benzene-1,2-diamine, see: Gdaniec et al. (2004 ▶).

Experimental

Crystal data

C₁₇H₁₃N₄ ⁺·BF₄ ⁻
M _r = 360.12
Orthorhombic,
a = 7.3412 (2) Å
b = 17.5051 (5) Å
c = 12.2426 (3) Å
V = 1573.28 (7) Å³
Z = 4
Mo Kα radiation
μ = 0.13 mm⁻¹
T = 183 K
0.44 × 0.31 × 0.11 mm

Data collection

Oxford Diffraction Xcalibur diffractometer with a Ruby detector
Absorption correction: analytical [CrysAlis PRO (Oxford Diffraction, 2010 ▶) based on Clark & Reid (1995 ▶)] T _min = 0.964, T _max = 0.991
8816 measured reflections
2014 independent reflections
1543 reflections with I > 2σ(I)
R _int = 0.022

Refinement

R[F ² > 2σ(F ²)] = 0.042
wR(F ²) = 0.117
S = 1.08
2014 reflections
130 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.27 e Å⁻³
Δρ_min = −0.36 e Å⁻³

Data collection: CrysAlis PRO (Oxford Diffraction, 2010 ▶); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: Mercury (Macrae et al., 2006 ▶), ORTEP-3 for Windows (Farrugia, 1997) ▶ and POV-RAY for Windows (Cason, 2003 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶) and publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536811027942/su2291sup1.cif

e-67-o2066-sup1.cif^{(14KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811027942/su2291Isup2.hkl

e-67-o2066-Isup2.hkl^{(97.1KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811027942/su2291Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1⋯F3	0.95 (2)	2.14 (2)	3.094 (2)	178 (2)
C9—H9⋯F1ⁱ	0.93	2.62	3.4759 (19)	154

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Symmetry code: (i) Inline graphic .

supplementary crystallographic information

Comment

N,N'-bis(2-pyridyl)aryldiamines are an important class of compounds that are useful as intermediates in the syntheses of organic electroluminescent devices (LED) (Stoessel et al., 2010), or as compounds useful for altering the lifespan of eukaryotic organisms in the yeast (Goldfarb, 2009). Imidazolium salts based on the benzoimidazole scaffold are used in electronics (Bold et al., 2005; Murakami et al., 2007) and in catalytic processes involving the use of the benzimidazolium salt as it is (Teles et al., 1996), or bound to a metal (Berlin et al., 2007; Huang et al., 2005).

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, C₁₇H₁₃N₄⁺.BF₄^-, 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)°.

In the crystal intermolecular C—H···F interactions link the cations and anions into layers parallel to the (100) crystallographic plane (Fig. 2, Table 1). The crystal packing is further stabilizes by F···π contacts (Fig. 3) involving the tetrafluoridoborate anions and the five-membered rings of the benzimidazole rings [F···centroid = 2.811 (2) Å].

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 NH₄OH 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%).

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.