1-(1H-Benzimidazol-1-ylmeth­yl)-3-[2-(di­isopropyl­amino)eth­yl]-1H-benzimid­azolium bromide 0.25-hydrate

Hakan Arslan; Don VanDerveer; Serpil Demir; İsmail Özdemir; Bekir Çetinkaya

doi:10.1107/S160053680900765X

. 2009 Mar 6;65(Pt 4):o699–o700. doi: 10.1107/S160053680900765X

1-(1H-Benzimidazol-1-ylmethyl)-3-[2-(diisopropylamino)ethyl]-1H-benzimidazolium bromide 0.25-hydrate

Hakan Arslan ^a,^b,^*, Don VanDerveer ^c, Serpil Demir ^d, İsmail Özdemir ^d, Bekir Çetinkaya ^e

PMCID: PMC2969106 PMID: 21582439

Abstract

The title N-heterocyclic carbene derivative, C₂₃H₃₀N₅ ⁺·Br⁻·0.25H₂O, was synthesized using microwave heating and was characterized by ¹H and ¹³C NMR spectroscopy and a single-crystal X-ray diffraction study. The structure of the title compound are stabilized by a network of intra- and intermolecular C—H⋯Br hydrogen-bonding interactions. The crystal structure is further stabilized by π–π stacking interactions between benzene and imidazole fragment rings of parallel benzo[d]imidazole rings, with a separation of 3.486 (3) Å between the centroids of the benzene and imidazole rings. There is also an intermolecular C—H⋯π interaction in the crystal structure. The C—N bond lengths for the central benzimidazole ring are shorter than the average single C—N bond, thus showing varying degrees of double-bond character and indicating partial electron delocalization within the C—N—C—N—C fragment. The isopropyl group is disordered over two sites with occupancies of 0.792 (10) and 0.208 (10).

Related literature

For the synthesis, see: Yaşar et al. (2008 ▶). For general background, see: Herrmann et al. (1995 ▶); Navarro et al. (2006 ▶); Arduengo & Krafczyc (1998 ▶); Larhed et al. (2002 ▶); Leadbeater & Shoemaker (2008 ▶). For related compounds, see: Özel Güven et al. (2008a ▶,b ▶,c ▶); Türktekin et al. (2004 ▶); Akkurt et al. (2004 ▶, 2005 ▶, 2007a ▶,b ▶); Arslan et al. (2005 ▶, 2007 ▶, 2009 ▶ and references therein).

Experimental

Crystal data

C₂₃H₃₀N₅ ⁺·Br⁻·0.25H₂O
M _r = 460.93
Triclinic,
a = 8.4944 (17) Å
b = 9.4960 (19) Å
c = 15.318 (3) Å
α = 83.29 (3)°
β = 84.69 (3)°
γ = 65.93 (3)°
V = 1119.1 (5) Å³
Z = 2
Mo Kα radiation
μ = 1.86 mm⁻¹
T = 153 K
0.34 × 0.12 × 0.10 mm

Data collection

Rigaku Mercury CCD diffractometer
Absorption correction: multi-scan (REQAB; Jacobson, 1998 ▶) T _min = 0.571, T _max = 0.836
7638 measured reflections
3889 independent reflections
2390 reflections with I > 2σ(I)
R _int = 0.039

Refinement

R[F ² > 2σ(F ²)] = 0.054
wR(F ²) = 0.144
S = 0.98
3889 reflections
282 parameters
22 restraints
H-atom parameters constrained
Δρ_max = 0.74 e Å⁻³
Δρ_min = −0.71 e Å⁻³

Data collection: CrystalClear (Rigaku/MSC, 2006 ▶); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S160053680900765X/hg2484sup1.cif

e-65-0o699-sup1.cif^{(24.5KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S160053680900765X/hg2484Isup2.hkl

e-65-0o699-Isup2.hkl^{(190.6KB, hkl)}

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⋯Br1	0.96	2.75	3.493 (7)	135
C6—H6⋯Br1ⁱ	0.96	2.75	3.702 (6)	173
C20—H20A⋯Cg1	0.96	2.95	3.445 (5)	113

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Symmetry code: (i) Inline graphic . Cg1is the centroid of the N1,C1,N2,C7,C2 ring.

Acknowledgments

We thank the İnönü University Research Fund (İÜ BAP: 2008/Güdümlü 3) for financial support.

supplementary crystallographic information

Comment

N-Heterocyclic carbene compounds have been shown to have wide applicability in organometallic chemistry and catalysis such as Suzuki-Miyura, Sonogashira, Stille and Heck reactions (Herrmann et al., 1995; Navarro et al., 2006; Arduengo & Krafczyc, 1998). In general, N-heterocyclic carbene chemistry is dominated by imidazole, diazepin, benzimidazole and their derivatives based carbene ligands.

Microwave-promoted synthesis is an area of increasing interest in both academic and industrial laboratories (Larhed et al., 2002). Microwave heating offers a fast, easy way to perform chemical reactions that require heat. Synthetic organic chemists have taken advantage of microwave heating in their work and found that reaction times can often be reduced from hours to minutes with a significant improvement in yields (Leadbeater & Shoemaker, 2008).

Our team has been interested in complexes of derivatives based on N-heterocyclic carbene compounds which exhibit high catalytic activities for Suzuki-Miyura, and Heck reactions. As a continuation of our systematic studies of the various N-heterocyclic carbene compounds and the catalytic properties of their palladium, ruthenium and rhodium complexes (Yaşar et al., 2008; Arslan et al., 2005, 2007, 2009, and references therein), we have prepared a new carbene compound which includes a benzo[d]imidazole and an amine group. The title compound, (I), synthesis and characterization, including its crystal structure is reported here. The compound was purified by re-crystallizationfrom an ethanol:diethylether mixture (1:2) and characterized by ¹H and ¹³C-NMR. These data are consistent with the proposed structure given in Scheme 1.

The crystallographic asymmetric unit of the title compound contains a single 3-((1H-benzo[d]imidazol-1-yl)methyl)-1-(2-(diisopropylamino)ethyl)-1H-benzo[d]imidazol-3-ium cation, one bromide anion and 0.25 mole water molecule linked by hydrogen and stacking interactions to form a three-dimensional framework. The molecular structure of the title compound is depicted in Fig. 1.

The imidazole and benzimidazole ring systems are essentially planar with maximum deviations of 0.002 (5), 0.008 (5), 0.029 (5) and 0.020 (5) Å for N1—C1—N2—C7—C2, N3—C9—N4—C11—C16, N1—C1—N2—C7—C2—C3—C4—C5—C6 and N3—C9—N4—C11—C12—C13—C14—C15 rings, respectively. The dihedral angle between the benzimidazole rings is 69.51 (8)^o. The geometric parameters for the N3—C9—N4—C11—C12—C13—C14—C15 benzimidazole ring agree with the other reported benzimidazole derivatives (Özel Güven et al., 2008a, 2008b, 2008c; Türktekin et al., 2004; Akkurt et al., 2004, 2005, 2007a, 2007b). In particular, in the N—C—N fragments, the C9—N4 bond length (1.295 (8) Å) is ca 0.08 Å shorter than the C9—N3 bond length (1.367 (9) Å), which is consistent with the partial double-bond character. The C—N bond lengths for the other benzimidazole ring are shorter than the average single C—N bond, being N1—C1 = 1.332 (7) Å, N2—C1 = 1.332 (9) Å, N1—C2 = 1.398 (7) Å, and N2—C7 = 1.399 (6) Å thus showing varying degrees of double bond character in these C—N bonds. This information indicates a partial electron delocalization within the C2—N1—C1—N2—C7 fragment. This result is confirmed by the N1—C1—N2 bond angle.

The crystal packing is stabilized mainly by C—H···Br hydrogen bonds and stacking interactions. A partially overlapped arrangement is observed between parallel benzimidazole rings (see Fig. 2) so these parallel benzimidazole rings are linked by π-π stacking interactions. The centroid-centroid separation between the parallel imidazole and benzene ring fragments (N1—C1—N2—C7—C2ⁱand C2—C3—C4—C5—C6—C7ⁱ) of the benzimidazole ring is 3.486 (3) Å with C1···C4ⁱⁱ = 3.398 (7) Å [symmetry code: (i) x, y, z, (ii) 1 - x, 1 - y, 1 - z]. In addition, a C—H···π interaction is observed between Cg1 (Centroid of N1—C1—N2—C7—C2 ring) and the C20 atom: H20A···Cg1ⁱ = 2.950 Å, C20—H20A···Cg1ⁱ = 113.0° [symmetry code: (i) x, y, z].

Experimental

All reactions for the preparation of (II) and (III) were carried out under Ar inflame-dried glass-ware using standard Schlenk-type flasks (Fig. 3). All ¹H and ¹³C-NMRs were performed in CDCl_3.¹H NMR and ¹³C NMR spectra were recorded using a Varian As 400 Merkur spectrometer operating at 400 MHz (¹H) and 100 MHz (¹³C). Chemical shifts (δ) are given in p.p.m. relative to TMS, coupling constants (J) in Hz. Melting points were measured in open capillary tubes with an Electrothermal-9200 melting point apparatus and are uncorrected. Microwave assisted reactions were carried out in a self-tuning single mode CEM Discover microwave unit. This consist of a continuous focused microwave power delivery system with operator-selectable power output from 0 to 300 W. The reaction was performed in an 80 ml capacity sealed tube. Temperature, pressure and power profiles were monitored using commercially available software provided by the microwave manufacturer.

Dibromomethane (1.74 g, 10.0 mmol) was slowly added to a solution of N-(2-(1H-benzo[d]imidazol-1-yl)ethyl)-N-isopropylpropan-2-amine (II) (2.45 g, 10.0 mmol) in DMF (5 ml) and the resulting mixture was stirred at 50 ^oC for 5 h (Fig. 3). Diethylether (10 ml) was added to obtain a white crystalline solid which was filtered off. The solid was washed with diethylether (3x10 ml), dried under vacuum and the crude product (III) was recrystallized from ethanol:diethylether. The yield was 2.72 g, 65%. In a dry 80 ml glass vessel equipped with a magnetic stirbar were added a potassium hydroxide (1 mmol) solution of benzimidazole (1 mmol) in ethanol (20 ml) and compound (III) (1 mmol). The vessel was sealed with a septum and placed in the microwave apparatus. With stirring, the reaction mixture was heated to 100 ^oC using an initial microwave power of 300 W and was held at this temperature for 10 min. The reaction mixture was then cooled to 50 ^oC, the solid was filtered off. The solvent was removed under vacuum. The product (I) was recrystallized from ethanol:diethylether (1: 2 ratio). The yield was 3.47 g, 76%, M.p.= 208–209 ^oC. ¹H NMR (δ, 399.9 MHz, CDCl₃): 0.87 (d, 12H, J= 6.6 Hz, NCH(CH₃)₂), 2.98 (t, 2H, J = 6.0 Hz, NCH₂CH₂N), 3.04 (hept, 2H, J = 6.6 Hz, NCH(CH₃)₂), 4.58 (t, 2H, J = 6.0 Hz, NCH₂CH₂N), 5.98 (s, 2H, –CH₂–), 7.61–7.77 (m, 9H, C₆H₄and NCH=N), 10.96 (s, 1H, NCHN). ¹³C NMR (δ, CDCl₃): 20.8 (NCH(CH₃)₂), 44.5 (NCH₂CH₂N), 47.8 (NCH(CH₃)₂), 48.2 (-CH₂–), 112.7, 113.2, 126.4, 126.7, 130.5 and 131.4 (C₆H₄), 143.4 (NCH=N), 143.6 (NCHN).