3,3′-Bis(3-methoxy­benz­yl)-1,1′-ethyl­enediimidazolium dibromide

In the title compound, C₂₄H₂₈N₄O₂²⁺·2Br⁻, the imidazolium cation is located on an inversion centre. The two imidazole rings are parallel to each other, whereas the imidazole and benzene rings make a dihedral angle of 77.25 (16)°. Non­classical inter­molecular C—H...Br hydrogen bonds link the imidazolium cations and the bromide anions into a three-dimensional network.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.0515
• wR factor = 0.143
• Data-to-parameter ratio = 18.0

checkCIF/PLATON results

No syntax errors found



Alert level C
            Value of measurement temperature given =   298.000
            Value of melting point given =     0.000
PLAT241_ALERT_2_C Check High      Ueq as Compared to Neighbors for         C5

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   1 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

S1. Comment

In the past decade, N-heterocyclic carbenes (NHCs) and their palladium complexes have attracted much interest due to their catalytic activities in C—C coupling reactions (Hillier et al., 2002). The structure of 1,1'-bis(3-methoxybenzyl)-3,3'-methylenediimidazolium dibromide has already been reported (Lee & Chiu, 2004). The structures of other related bis(imidazolium) salts have also been reported (Cheng et al., 2006; Lee et al., 2007).

One of the common methods for the preparation of palladium NHC complexes is a one-pot reaction between an imidazolium salt and a palladium precursor in the presence of base (Lee et al., 2004). By this method, we prepared a palladium bis(NHC) complex from the title compound. Here, we report the crystal structure of the title compound.

The structure of the title compound is shown in Fig. 1. The bis(imidazolium) dication is located on an inversion center, with the two imidazole rings parallel to each other. The imidazole and benzene rings make a dihedral angle of 77.25 (16)°. The bromide anions are involved in intermolecular hydrogen bonds of the type C—H···Br with the imidazolium cations, forming a three-dimensional hydrogen-bonded network (Fig. 2 and Table 1).

Related literature

For the structure of 1,1'-bis(3-methoxybenzyl)-3,3'-methylenediimidazolium dibromide see: Lee & Chiu (2004). For the structures of other related bis(imidazolium) salts, see: Cheng et al. (2006); Lee et al. (2004); Lee et al. (2007). For a review of N-heterocyclic carbenes, see: Hillier et al. (2002)

S2. Experimental

The compound was prepared according to the literature procedure (Lee et al., 2004). Suitable crystals were obtained by slow diffusion of diethyl ether into a DMF solution of the compound at room temperature. The average dimensions of the colorless, rod-like crystals are about 0.35 x 0.20 x 0.20 mm.

S3. Refinement

All hydrogen atoms could have been located in the difference Fourier map; nevertheless, they were all positioned geometrically and refined as riding atoms, with C_aryl—H = 0.93, C_methyl —H = 0.96, C_methylene—H = 0.97 Å; U_iso(H) = 1.5U_eq(C) for the methyl H atoms and U_iso(H) = 1.2U_eq(C) for all the other H atoms.

Computing details

Data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 (Bruker, 2004); data reduction: APEX2 (Bruker, 2004); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The structure of the title compound, showing 50% probability displacement ellipsoids for the non-hydrogen atoms. The H atoms are depicted as circles of arbitrary radius. The unlabelled atoms of the imidazolium cation are related to the labelled ones by 3/2 - x, 3/2 - y, -z; for the anion, the symmetry operation for Br1 is 1 - x + 1, y, 1/2 - z.
	Fig. 2. A view of the crystal packing along the b axis. Hydrogen bonds are shown as dashed lines.

3,3'-Bis(3-methoxybenzyl)-1,1'-ethylenediimidazolium dibromide

Crystal data

C24H28N4O2^2+·2Br^−	F(000) = 572
Mr = 564.32	Dx = 1.546 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1952 reflections
a = 18.340 (6) Å	θ = 3.3–26.3°
b = 5.3566 (17) Å	µ = 3.37 mm^−1
c = 12.340 (4) Å	T = 298 K
β = 91.491 (9)°	Rod, white
V = 1211.9 (7) Å^3	0.35 × 0.20 × 0.15 mm
Z = 2

Data collection

Bruker SMART APEXII diffractometer	2609 independent reflections
Radiation source: fine-focus sealed tube	1838 reflections with I > 2σ
Graphite monochromator	Rint = 0.050
ω scans	θmax = 27.0°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −14→23
Tmin = 0.366, Tmax = 0.600	k = −6→6
6855 measured reflections	l = −14→15

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.052	Hydrogen site location: difference Fourier map
wR(F^2) = 0.143	H-atom parameters constrained
S = 1.00	w = 1/[σ^2(Fo^2) + (0.0825P)^2 + 0.0975P] where P = (Fo^2 + 2Fc^2)/3
2609 reflections	(Δ/σ)max = 0.001
145 parameters	Δρmax = 0.71 e Å^−3
0 restraints	Δρmin = −1.24 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² 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 (Ų)

	x	y	z	Uiso*/Ueq
N1	0.43660 (17)	0.3916 (6)	0.1046 (3)	0.0292 (7)
N2	0.33797 (15)	0.2134 (6)	0.1563 (2)	0.0272 (7)
O1	0.09061 (18)	0.8336 (7)	0.1978 (3)	0.0551 (9)
Br1	0.34564 (2)	0.59558 (9)	0.39315 (4)	0.0443 (2)
C1	0.3639 (2)	0.4034 (7)	0.1010 (3)	0.0318 (9)
H1A	0.3361	0.5252	0.0655	0.038*
C2	0.3950 (2)	0.0735 (7)	0.1966 (3)	0.0305 (9)
H2A	0.3917	−0.0702	0.2385	0.037*
C3	0.4573 (2)	0.1845 (8)	0.1637 (3)	0.0331 (9)
H3A	0.5048	0.1309	0.1783	0.040*
C4	0.4858 (2)	0.5616 (7)	0.0499 (3)	0.0301 (9)
H4A	0.5262	0.6056	0.0984	0.036*
H4B	0.4600	0.7136	0.0299	0.036*
C5	0.2612 (2)	0.1516 (9)	0.1779 (4)	0.0478 (13)
H5A	0.2538	0.1573	0.2554	0.057*
H5B	0.2511	−0.0173	0.1534	0.057*
C6	0.2085 (2)	0.3286 (8)	0.1218 (4)	0.0353 (10)
C7	0.1942 (2)	0.3068 (10)	0.0106 (4)	0.0504 (12)
H7A	0.2172	0.1854	−0.0300	0.060*
C8	0.1452 (3)	0.4690 (11)	−0.0375 (4)	0.0549 (13)
H8A	0.1360	0.4578	−0.1119	0.066*
C9	0.1094 (2)	0.6460 (9)	0.0203 (4)	0.0470 (12)
H9A	0.0763	0.7530	−0.0142	0.056*
C10	0.1230 (2)	0.6648 (8)	0.1315 (4)	0.0375 (10)
C11	0.1735 (2)	0.5067 (9)	0.1817 (4)	0.0361 (9)
H11A	0.1835	0.5211	0.2557	0.043*
C12	0.0360 (3)	0.9930 (12)	0.1522 (5)	0.0641 (15)
H12A	0.0182	1.1019	0.2073	0.096*
H12B	−0.0035	0.8940	0.1231	0.096*
H12C	0.0564	1.0909	0.0953	0.096*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0268 (16)	0.0313 (18)	0.0295 (17)	−0.0003 (13)	0.0001 (13)	0.0021 (14)
N2	0.0241 (16)	0.0276 (18)	0.0298 (17)	0.0021 (13)	−0.0011 (13)	0.0040 (14)
O1	0.053 (2)	0.053 (2)	0.060 (2)	0.0171 (16)	−0.0040 (16)	−0.0099 (17)
Br1	0.0467 (3)	0.0480 (3)	0.0380 (3)	−0.0161 (2)	−0.00102 (19)	0.0012 (2)
C1	0.030 (2)	0.030 (2)	0.036 (2)	0.0073 (16)	−0.0012 (16)	0.0039 (17)
C2	0.029 (2)	0.030 (2)	0.032 (2)	−0.0002 (16)	−0.0018 (16)	0.0090 (17)
C3	0.029 (2)	0.036 (2)	0.034 (2)	0.0047 (17)	−0.0043 (16)	0.0071 (18)
C4	0.031 (2)	0.031 (2)	0.028 (2)	−0.0029 (16)	−0.0002 (16)	0.0006 (16)
C5	0.021 (2)	0.051 (3)	0.071 (3)	−0.0005 (19)	0.004 (2)	0.024 (2)
C6	0.0225 (19)	0.037 (2)	0.047 (2)	−0.0039 (17)	−0.0012 (17)	0.0074 (19)
C7	0.038 (3)	0.059 (3)	0.055 (3)	0.008 (2)	0.007 (2)	−0.008 (3)
C8	0.054 (3)	0.075 (4)	0.036 (3)	0.009 (3)	−0.006 (2)	−0.002 (2)
C9	0.036 (2)	0.055 (3)	0.049 (3)	0.011 (2)	−0.006 (2)	0.010 (2)
C10	0.029 (2)	0.037 (2)	0.046 (3)	−0.0011 (18)	0.0003 (18)	−0.0017 (19)
C11	0.028 (2)	0.043 (2)	0.038 (2)	−0.0042 (19)	−0.0045 (17)	0.003 (2)
C12	0.052 (3)	0.056 (3)	0.084 (4)	0.020 (3)	0.003 (3)	−0.006 (3)

Geometric parameters (Å, º)

N1—C1	1.334 (5)	C5—H5A	0.9700
N1—C3	1.375 (5)	C5—H5B	0.9700
N1—C4	1.460 (5)	C6—C11	1.376 (6)
N2—C1	1.321 (5)	C6—C7	1.396 (6)
N2—C2	1.369 (5)	C7—C8	1.374 (7)
N2—C5	1.477 (5)	C7—H7A	0.9300
O1—C10	1.366 (5)	C8—C9	1.365 (7)
O1—C12	1.422 (6)	C8—H8A	0.9300
C1—H1A	0.9300	C9—C10	1.391 (6)
C2—C3	1.360 (6)	C9—H9A	0.9300
C2—H2A	0.9300	C10—C11	1.389 (6)
C3—H3A	0.9300	C11—H11A	0.9300
C4—C4^i	1.502 (7)	C12—H12A	0.9600
C4—H4A	0.9700	C12—H12B	0.9600
C4—H4B	0.9700	C12—H12C	0.9600
C5—C6	1.509 (6)
C1—N1—C3	108.6 (3)	C6—C5—H5B	109.2
C1—N1—C4	125.7 (3)	H5A—C5—H5B	107.9
C3—N1—C4	125.6 (3)	C11—C6—C7	120.5 (4)
C1—N2—C2	109.1 (3)	C11—C6—C5	119.5 (4)
C1—N2—C5	128.6 (3)	C7—C6—C5	120.0 (4)
C2—N2—C5	122.3 (3)	C8—C7—C6	118.5 (5)
C10—O1—C12	118.2 (4)	C8—C7—H7A	120.8
N2—C1—N1	108.6 (3)	C6—C7—H7A	120.8
N2—C1—H1A	125.7	C9—C8—C7	122.1 (5)
N1—C1—H1A	125.7	C9—C8—H8A	119.0
C3—C2—N2	107.0 (3)	C7—C8—H8A	119.0
C3—C2—H2A	126.5	C8—C9—C10	119.4 (4)
N2—C2—H2A	126.5	C8—C9—H9A	120.3
C2—C3—N1	106.7 (3)	C10—C9—H9A	120.3
C2—C3—H3A	126.6	O1—C10—C11	115.5 (4)
N1—C3—H3A	126.6	O1—C10—C9	124.7 (4)
N1—C4—C4^i	109.6 (4)	C11—C10—C9	119.7 (4)
N1—C4—H4A	109.7	C6—C11—C10	119.9 (4)
C4^i—C4—H4A	109.7	C6—C11—H11A	120.1
N1—C4—H4B	109.7	C10—C11—H11A	120.1
C4^i—C4—H4B	109.7	O1—C12—H12A	109.5
H4A—C4—H4B	108.2	O1—C12—H12B	109.5
N2—C5—C6	112.3 (3)	H12A—C12—H12B	109.5
N2—C5—H5A	109.2	O1—C12—H12C	109.5
C6—C5—H5A	109.2	H12A—C12—H12C	109.5
N2—C5—H5B	109.2	H12B—C12—H12C	109.5

Symmetry code: (i) −x+1, −y+1, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2A···Br1^ii	0.93	2.77	3.657 (4)	161
C3—H3A···Br1^iii	0.93	2.91	3.729 (4)	148
C4—H4B···Br1^iv	0.97	2.85	3.669 (4)	143

Symmetry codes: (ii) x, y−1, z; (iii) −x+1, y−1/2, −z+1/2; (iv) x, −y+3/2, z−1/2.