1-(4-tert-Butylbenzyl)-3-(3,4,5-trimethoxybenzyl)benzimidazolium bromide monohydrate

A novel N-heterocyclic carbene derivative, C28H33N2O3 +·Br−·H2O, was synthesized and characterized by elemental analysis, 1H and 13C-NMR and IR spectroscopy and a single-crystal X-ray diffraction study. Ions of the title compound are linked by π⋯π stacking interactions (face–face separation 3.441 Å) and C—H⋯Br and O—H⋯Br interactions. Intra- and intermolecular C—H⋯O interactions are also present. The C—N bond lengths for the compound [1.329 (3), 1.325 (3), 1.389 (3) and 1.391 (3) Å] are all shorter than the average single C—N bond length of 1.48 Å, thus showing varying degrees of double-bond character.

Recently, we have focused on the synthesis, characterization and use of palladium, platinum and ruthenium N-heterocyclic carbene complexes as catalysts for Suzuki-Miyura and Heck reactions (Yaşar et al., 2008;Arslan et al., 2009, and references therein).
In the present work, we report the preparation and characterization of a novel N-heterocyclic carbene derivative, 1-(4tert-butylbenzyl)-3-(3,4,5-trimethoxybenzyl)benzimidazolium bromide monohydrate, (I). The compound was purified by re-crystallization from ethanol:diethylether mixture (1:1) and characterized by elemental analysis, 1 H and 13 C-NMR and IR spectroscopy. The analytical and spectroscopic data are consistent with the proposed structure given in Scheme 1.
The molecular structure of the title compound is depicted in Figure 1. The crystal structure is composed of a 1-(4-tertbutylbenzyl)-3-(3,4,5-trimethoxybenzyl)benzimidazolium cation, a Br anion and solvent water molecules. All bond lengths in (I) are in normal ranges (Allen et al.,1987). The benzimidazole ring is almost coplanar with a maximum and a minimum deviation of 0.016 (2) Å for atom C2 and, 0.002 (2) Å for atom C6, respectively. In the crystal structure, π···π stacking interactions occurs between parallel benzimidazole rings, with a face-face separation of 3.441 Å ( The crystal packing is shown in Figure 3. The intermolecular C-H···Br and O-H···Br hydrogen bonds ( Figure 4, Table   1) and π···π stacking interactions link the molecules of the title compound.

Refinement
All H atoms attached to carbons were geometrically fixed and allowed to ride on the corresponding non-H atom with C-H = 0.96 Å, and U iso (H) = 1.5U eq (C) of the attached C atom for methyl H atoms and 1.2U eq (C) for other H atoms. The water H atoms were located from a Fourier map and their distances were constrained to 0.86 Å and the U iso (H) = 1.5U eq (O). Fig. 1. The molecular structure of the title compound, showing the atom-numbering scheme and displacement ellipsoids drawn at the 50% probability level.    1-(4-tert-Butylbenzyl)-3-(3,4,5-trimethoxybenzyl)benzimidazolium bromide monohydrate

Special details
Geometry. All e.s. 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.