1,3-Bis(2-cyanobenzyl)imidazolium bromide

In the title salt, C19H15N4 +·Br−, the central imidazole ring makes dihedral angles of 83.1 (2) and 87.6 (2)° with the terminal benzene rings. The dihedral angle between the terminal benzene rings is 6.77 (19)°; the cyanide substituents have an anti orientation. In the crystal, the cations and anions are linked via C—H⋯N and C—H⋯Br hydrogen bonds, forming sheets lying parallel to the ac plane.

In the title salt, C 19 H 15 N 4 + ÁBr À , the central imidazole ring makes dihedral angles of 83.1 (2) and 87.6 (2) with the terminal benzene rings. The dihedral angle between the terminal benzene rings is 6.77 (19) ; the cyanide substituents have an anti orientation. In the crystal, the cations and anions are linked via C-HÁ Á ÁN and C-HÁ Á ÁBr hydrogen bonds, forming sheets lying parallel to the ac plane.

Comment
Since the investigation of N-heterocyclic carbene (NHC) chemistry by Wanzlick and Kleiner (1961), NHCs have played a major role as ligands in coordination and organometallic chemistry (Fahlbusch et al., 2009). During the past decades it has been proven as an alternative to tertiary phosphines in homogeneous catalysis. Due to NHC's strong σ-donating and negligible π-accepting characters, they are compatible with metals in a variety of oxidation states. NHC can stabilize catalytically active intermediates (Demir et al., 2009) making it a very versatile ligand system. NHC complexes with every transition metal are now known and their applications especially in the area of catalysis cover a broad spectrum such as hydroboration (Grasa et al., 2002), polymerization reactions (Buchowicz et al., 2006) and hydrosilation (Marko et al., 2002).
Furthermore, NHCs are easy to handle, stable and inexpensive resulting in their receiving a great deal of interest compared to other types of carbenes.
In the crystal, (Fig. 2), the cations and anions are linked via C-H···N and C-H···Br hydrogen bonds (Table 1), forming two-dimensional networks parallel to the ac-plane.
Experimental Imidazole (0.3 g, 3.7 mmol) and potassium hydroxide (0.2 g, 5.5 mmol) was stirred for 2 h in 25 mL of ethanol. 2-Bromomethyl benzonitrile (1.8 g, 9.2 mmol) was then added and the mixture was refluxed at 80°C for 24 h. The resulting clear crystals were isolated by decantation, washed with fresh n-hexane (2 X 3 ml) and then left to dry at ambient temperature. Yield: 1.3 g, (94%); m.p: 233-234°C. Colourless blocks were obtained by slow evaporation of the salt solution in ethanol at ambient temperature.

Refinement
All hydrogen atoms were positioned geometrically [ C-H = 0.93 or 0.97 Å] and were refined using a riding model, with Fig. 1. The asymmetric unit of the title compound, showing 30% probability displacement. 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.