3,3′-Dibenzyl-1,1′-(2,4,6-trimethyl-m-phenyl­enedimethyl­ene)diimidazol-3-ium dibromide

Rosenani A Haque; Abbas Washeel Salman; Paremala Nadarajan; Madhukar Hemamalini; Hoong-Kun Fun

doi:10.1107/S1600536811005204

. 2011 Feb 16;67(Pt 3):o643. doi: 10.1107/S1600536811005204

3,3′-Dibenzyl-1,1′-(2,4,6-trimethyl-m-phenylenedimethylene)diimidazol-3-ium dibromide

Rosenani A Haque ^a, Abbas Washeel Salman ^a, Paremala Nadarajan ^a, Madhukar Hemamalini ^b, Hoong-Kun Fun ^b,^*,^‡

PMCID: PMC3051991 PMID: 21522396

Abstract

In the title molecular salt, C₃₁H₃₄N₄ ²⁺·2Br⁻, the central benzene ring makes dihedral angles of 80.47 (12) and 82.78 (12)° with the adjacent imidazole rings. The dihedral angle between the two terminal phenyl rings is 79.16 (13)°. In the crystal, the cations and anions are linked via C—H⋯Br hydrogen bonds, forming supramolecular chains along the c axis.

Related literature

For applications of N-heterocyclic carbenes (NHCs), see: Winkelmann & Navarro (2010 ▶); Papini et al. (2008 ▶); Marion et al. (2007 ▶); Burstein & Glorius (2004 ▶); Sohn et al. (2004 ▶); Grasa et al. (2002 ▶); Singh & Nolan (2005 ▶). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986 ▶).

Experimental

Crystal data

C₃₁H₃₄N₄ ²⁺·2Br⁻
M _r = 622.44
Monoclinic,
a = 8.9851 (2) Å
b = 12.8044 (2) Å
c = 25.6419 (5) Å
β = 102.611 (1)°
V = 2878.90 (10) Å³
Z = 4
Mo Kα radiation
μ = 2.84 mm⁻¹
T = 100 K
0.49 × 0.43 × 0.21 mm

Data collection

Bruker SMART APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2009 ▶) T _min = 0.337, T _max = 0.585
32884 measured reflections
8490 independent reflections
6550 reflections with I > 2σ(I)
R _int = 0.036

Refinement

R[F ² > 2σ(F ²)] = 0.040
wR(F ²) = 0.101
S = 1.04
8490 reflections
337 parameters
H-atom parameters constrained
Δρ_max = 1.28 e Å⁻³
Δρ_min = −0.40 e Å⁻³

Data collection: APEX2 (Bruker, 2009 ▶); cell refinement: SAINT (Bruker, 2009 ▶); data reduction: SAINT; 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 and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811005204/wn2422sup1.cif

e-67-0o643-sup1.cif^{(26.3KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811005204/wn2422Isup2.hkl

e-67-0o643-Isup2.hkl^{(407KB, 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
C7—H7A⋯Br2	0.97	2.90	3.754 (2)	147
C7—H7B⋯Br1ⁱ	0.97	2.92	3.787 (2)	149
C8—H8A⋯Br2	0.93	2.81	3.496 (3)	132
C10—H10A⋯Br1ⁱ	0.93	2.74	3.565 (2)	148
C18—H18B⋯Br2ⁱⁱ	0.97	2.74	3.702 (2)	172
C19—H19A⋯Br1ⁱ	0.93	2.74	3.553 (2)	147
C21—H21A⋯Br2ⁱⁱⁱ	0.93	2.83	3.603 (3)	141

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

RAH thanks Universiti Sains Malaysia (USM) for the FRGS fund (203/PKIMIA/671115), short term grant (304/PKIMIA/639001) and RU grants (1001/PKIMIA/813023 and 1001/PKIMIA/811157). AWS thanks USM for the RU grant (1001/PKIMIA/843090). HKF and MH thank the Malaysian Government and USM for the Research University grant No. 1001/PFIZIK/811160. MH also thanks Universiti Sains Malaysia for a post-doctoral research fellowship.

supplementary crystallographic information

Comment

N-Heterocyclic carbenes (NHCs) have found widespread applications as ligands in organometallic chemistry during recent years (Winkelmann & Navarro, 2010). They typically have strong σ-donor properties but poor π-acceptor character and have been widely employed as alternatives to phosphine ligands to stabilise transition metal complexes. NHCs are relatively inexpensive, non-toxic and easily prepared from azolium salts (Papini et al., 2008). Notably, NHCs also exhibit excellent catalytic activity in metal-free organocatalysis (Marion et al., 2007) including umpolung and condensation of carbonyl compounds (Burstein & Glorius, 2004; Sohn et al., 2004) and transesterification reactions (Grasa et al., 2002; Singh & Nolan, 2005).

The asymmetric unit of the title compound, (Fig. 1), consists of one 1,3-bis(3-benzylimidazolium-1-ylmethyl)mesitylene cation and two bromide anions. The central benzene ring (C12–C17) makes dihedral angles of 80.47 (12)° and 82.78 (12)° with the adjacent imidazole rings (N1/N2/C8–C10) and (N3/N4/C19–C21). The dihedral angle between the two terminal phenyl rings (C1–C6) and (C23–C28) is 79.16 (13)°.

In the crystal structure (Fig. 2), the cations and anions are linked together via intermolecular C—H···Br (Table 1) hydrogen bonds, forming one-dimensional supramolecular chains along the c-axis.

Experimental

A mixture of imidazole (1.0 g, 14.0 mmol) and sodium hydroxide (0.6 g, 15.0 mmol) in DMSO (20 ml) was heated to 363 K for 2 h. The mixture was cooled at room temperature then 1,3-bis(bromomethyl)mesitylene (2.0 g, 6.5 mmol) in 10 ml of DMSO was added, heated to 413 K for 1 h and poured into water (200 ml), then cooled in an ice bath. The resulting precipitate was collected by filtration, washed with water (3x10 ml), and recrystallised from methanol/water to give 1,3-bis(N-imidazole-1-ylmethyl)mesitylene as an off-white solid (1.45 g, 79 %). Further, a mixture of 1,3-bis(N-imidazole-1-ylmethyl)mesitylene (0.7 g, 2.5 mmol) and benzyl bromide (1.0 g, 5.8 mmol) in 30 ml of acetonitrile, was refluxed for 24 h, then cooled to room temperature and left standing overnight, giving the title compound as light brown crystals which were isolated by decantation and washed with diethyl ether (2x5 ml) and placed in a desiccator. The yield was (1.15 g, 74%). The resulting crystals were suitable for X-ray diffraction.