N-(2-Bromobenzyl)-N′-(2-pyridyl)benzene-1,2-diamine

In the title compound, C18H16BrN3, molecules are linked into dimers by co-operative intermolecular N—H⋯N hydrogen bonding. Only one N—H group is involved in hydrogen bonding. The planes of the pyridine and bromophenyl rings are twisted by 61.49 (3) and 79.11 (8)°, respectively, from the plane of the central phenyl ring.

In the title compound, C 18 H 16 BrN 3 , molecules are linked into dimers by co-operative intermolecular N-HÁ Á ÁN hydrogen bonding. Only one N-H group is involved in hydrogen bonding. The planes of the pyridine and bromophenyl rings are twisted by 61.49 (3) and 79.11 (8) , respectively, from the plane of the central phenyl ring.

Related literature
The title compound was isolated as part of a project to further investigate the chemistry of chalcogen-carbene compounds (Dutton et al., 2007). The stability of imidazole-based carbenes depends very much on the nature of the substituents attached to the imidazole nitrogen atoms, see: Huynh et al. (2006); Kuhn et al. (1993). For bond lengths in analogous compounds, see: Albé niz et al. (2002); Denk et al. (2001). For details of the synthesis, see: Hahn et al. (2007).  Table 1 Hydrogen-bond geometry (Å , ).
HSB is grateful to the Department of Science and Technology (DST) for the award of a Ramanna Fellowship. STM thanks the CSIR for a JRF/SRF fellowship. RJB wishes to acknowledge the NSF-MRI program (grant CHE-0619278) for funds to purchase the diffractometer.

Comment
The structure of the title compound, C 18 H 16 BrN 3 , (2), is shown below. Dimensions are available in the archived CIF.
Carbene compounds sometimes show unpredictable reactivity patterns and are subject to hydrolysis (Denk et al. 2001;Albéniz et al., 2002). The stability of imidazole based carbenes depends very much on the nature of the substituents attached to the imidazole nitrogen atoms (Hahn et al., 2007;Huynh et al. 2006).
The title compound was isolated as part of a project to further investigate the chemistry of chalcogen-carbene compounds (Dutton et al., 2007), in particular tellurium-carbene chemistry with pyridine as a substituent on the nitrogen of the benzimidazole ring. However, in contrast with electron donating substituents such as n-butyl, and i-propyl, which lead to tellurium carbene formation, electron withdrawing groups such as phenyl and pyridyl result in hydrolysed products, such as the title compound. A repeated attempt to synthesize the pyridine substituted tellurone compound gave the title compound whose structure is reported here.
In (2) the bonds are in the usual ranges found for analogous compounds (Albéniz et al. 2002;Denk et al. 2001)).
The molecules are linked into dimers by cooperative intermolecular N-H···N hydrogen bonding. The two N-H moieties adopt different conformations with respect to the phenyl ring to which they are both attached. N1-H is only twisted by 18.0 (2)° from this plane. As a result of this coplanarity the hydrogen attached to N1 does not form any hydrogen bonds.
N2-H, however, is twisted by 51.8 (2)° from this plane so as to participate in the intermolecular hydrogen bonding mentioned above. The planes of the pyridine and bromo-phenyl rings are twisted by 61.49 (3)° and 79.11 (8)° from the plane of the central phenyl ring.
The cleavage of carbene carbon from benzimidazole ring in the title compound may be due to: 1) destabilization of C=Te by the electron withdrawing group present on the benzimidazolium nitrogen, 2) crowding near to the carbene carbon. The exact mechanism is under investigation. This structural study has confirmed the cleavage of the carbene carbon.

Experimental
In all cases, the starting benzylimidazoylium salt, 1, shown in scheme (1) was prepared using standard methods (Hahn et al. 2007). With the appropriate salt, the title compound could be made by three different methods: (a). In a round bottom flask the benzylimidazoylium salt 1 (1.0 mmol) was taken in THF (40 mL) under nitrogen atmosphere and of n-BuLi (2.0 mmol) was added at -78 °C, reaction mixture was stirred for 1-2 h. Then Te powder was added to the reaction mixture at room temperature, and stirred for 8-10 h. After completion of reaction, water (30 mL) was added and extracted with dichloromethane, dried over Na 2 SO 4 and evaporated. The residue obtained was dissolved in toluene and small amount of petroleum ether was added to separate the residue from the solution. The solution was filtered, evaporated and the residue was dissolved in diethyl ether and a small amount of petroleum ether (60-80 °C) to afford the pure colorless product in 45% yield.
supplementary materials sup-2 (b) The benzylimidazoylium salt 1 (1.0 mmol) was added to a brown solution of Na 2 Te 2 (2.0 mmol) at room temperature under nitrogen atmosphere and the reaction mixture was stirred for 6-10 h at room temperature. Then KO t Bu (1.0 mmol) was added to the reaction mixture and stirred further for 5-7 h. After completion of reaction, the reaction was quenched by adding water (50 mL), and extracted with dichloromethane, dried over Na 2 SO 4 , and evaporated. The residue obtained was dissolved in toluene and small amount of petroleum ether was added to separate the residue from the solution. The solution was filtered and evaporated; the residue was dissolved in diethyl ether and a small amount of petroleum ether (60-80 °C) to afford the pure crystalline product.
(c) In a round bottom flask the benzylimidazoylium salt 1 (1.0 mmol) was taken in THF (40 mL) under nitrogen atmosphere and Te metal powder (1.0 mmol) was added, then KO t Bu (2.0 mmol) was added to the reaction mixture at -20 °C.
The reaction mixture was stirred for 5-6 h. Then the reaction was quenched by adding water (50 mL), and extracted with dichloromethane, dried over Na 2 SO 4 , and evaporated. The residue obtained was dissolved in toluene and some petroleum ether was added to separate the residue from the solution. The solution was filtered and evaporated; the residue was dissolved in diethyl ether and small amount of petroleum ether (60-80 °C) to afford the pure product.  4, 148.4, 144.5, 138.1, 132.9, 128.9, 128.8, 127.8, 127.6, 127.4, 125.7, 123.4, 117.7, 114.6, 111.7, 107.4, 48.2      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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Br 0.83487 (5)