1-[Bicyclo[4.2.0]octa-1(6),2,4-trien-3-yl]-3-[bicyclo[4.2.0]octa-1(6),2,4-trien-3-yl­methyl]imidazolium hexa­fluoro­phos­phate

Fang-Hua Zhu; Jun-Xiao Yang; Zhi-Hua Mao; Ru-Gang Xie

doi:10.1107/S1600536807067086

. 2008 Jan 11;64(Pt 2):o434. doi: 10.1107/S1600536807067086

1-[Bicyclo[4.2.0]octa-1(6),2,4-trien-3-yl]-3-[bicyclo[4.2.0]octa-1(6),2,4-trien-3-ylmethyl]imidazolium hexafluorophosphate

Fang-Hua Zhu ^a, Jun-Xiao Yang ^b, Zhi-Hua Mao ^c, Ru-Gang Xie ^a,^*

PMCID: PMC2960209 PMID: 21201461

Abstract

In the title compound, C₂₀H₁₉N₂ ⁺·PF₆ ⁻, the two benzocyclobutene units are essentially planar and they form dihedral angles of 38.0 (2) and 72.7 (2)°, with the central imidazolium ring. In the crystal structure, weak C—H⋯π and π-–π stacking interactions [centroid–centroid distance = 3.742 (2) Å] contribute to the stability of the crystal structure. The PF₆ ⁻ ion is disordered over two positions with site occupancies of 0.869 (9) and 0.131 (9).

Related literature

For related literature, see: Farona (1996 ▶); Kirchhoff & Bruza (1993 ▶); Michellys et al. (2001 ▶); Nemeto & Fukumoto (1998 ▶); Zhang et al. (2006 ▶).

Experimental

Crystal data

C₂₀H₁₉N₂ ⁺·F₆P⁻
M _r = 432.34
Triclinic,
a = 9.311 (3) Å
b = 10.138 (3) Å
c = 10.562 (3) Å
α = 86.82 (2)°
β = 86.44 (2)°
γ = 73.61 (2)°
V = 953.9 (5) Å³
Z = 2
Mo Kα radiation
μ = 0.21 mm⁻¹
T = 296 (2) K
0.28 × 0.25 × 0.18 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
Absorption correction: none
3558 measured reflections
3522 independent reflections
2238 reflections with I > 2σ(I)
R _int = 0.006
3 standard reflections every 300 reflections intensity decay: 4.6%

Refinement

R[F ² > 2σ(F ²)] = 0.075
wR(F ²) = 0.223
S = 1.15
3522 reflections
299 parameters
81 restraints
H-atom parameters constrained
Δρ_max = 0.64 e Å⁻³
Δρ_min = −0.41 e Å⁻³

Data collection: DIFRAC (Gabe & White, 1993 ▶); cell refinement: DIFRAC; data reduction: NRCVAX (Gabe et al., 1989 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997 ▶); molecular graphics: ORTEPIII (Burnett & Johnson, 1996 ▶); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2003 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536807067086/ci2536sup1.cif

e-64-0o434-sup1.cif^{(21.9KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536807067086/ci2536Isup2.hkl

e-64-0o434-Isup2.hkl^{(172.7KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

Cg1 is the centroid of the C3–C8 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H2B⋯Cg1ⁱ	0.97	3.00	3.813 (5)	143

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Symmetry code: (i) Inline graphic .

Acknowledgments

The authors are grateful to the National Natural Science Foundation of China (grant No. 20574046) for financial support.

supplementary crystallographic information

Comment

Benzocyclobutenes (BCBs) are important building blocks for new polymers and advanced materials (Nemeto & Fukumoto, 1998; Michellys et al., 2001). Most of the reported benzocyclobutene monomers in the literature are bis-BCB-functionalized compounds owing to their highly crosslinked structure and their excellent properties such as the insolubility, low solvent pickup and good thermal stability (Farona, 1996; Zhang et al., 2006; Kirchhoff & Bruza, 1993). We report here the crystal structure of the title compound, a novel bisbenzocyclobutene-terminated imidazolium which was obtained by an anion metathesis between 1-(4-benzocyclobutenyl)-3-(4-benzocyclobutenylmethyl) imidazolium choloride and hexafluorophosphate ammonium.

The two benzocyclobutene units are essentially planar. The plane of the C1—C8 and C13—C20 benzocyclobutene units form dihedral angles of 38.0 (2) and 72.7 (2)°, respectively, with the central imidazolium ring.

A combination of intermolecular π-π and C—H···π interactions provide packing forces in the crystal structure of the title compound. A π-π interaction between C13—C15/C18—C20 benzene ring and its symmetry- related counterpart at (-x, 1 - y, -z), with their centroids separated by 3.742 (2) Å, plays an important part in the connection of two adjacent molecules. In addition, a weak C—H···π interaction between C2—H2B group and C3—C8 benzene ring at (1 - x, -1 - y, 1 - z) contributes to the crystal packing (Table 1).

Experimental

4-(N-imidazolyl)benzocyclobutene (5 mmol, 850 mg) and 4-cholomethylbenzocyclobutene (5 mmol, 760 mg) were placed in a two-necked round-bottomed flask under a nitrogen atmosphere, and the mixture was heated at 353 K for 3 h. After the reaction was completed, the resulting 1-(4-benzocyclobutenyl)-3-(4-benzocyclobutenylmethyl)imidazolium chloride, [BBMI][Cl^-], was obtained in 85% yield (1.381 g). [BBMI][Cl^-] was dissolved in deioned water, and NH₄PF₆ was added to replace Cl^- ions by PF₆^- ions, to obtain the title compound as a white solid (yield 1.331 g). Colourless crystals of the title compound were obtained by recrystallization of the solid from acetone and ethanol (1:1 v/v). ¹ H NMR (400 MHz, CDCl₃,): δ 8.84 (s, 1H), 7.41 (t, 1H), 7.31 (m, 2H), 7.27 (2 d, 1H), 7.22 (d, 1H), 7.18 (d, J = 8.0 Hz, 1H), 7.15 (s, 1H), 7.09 (d, J = 7.6 Hz, 1H), 5.37 (s, 2H), 3.21 (s, 4H), 3.17 (s, 4H); ¹³C NMR (100 MHz, CDCl₃,): δ 148.58, 148.04, 7.65, 147.21, 133.71, 133.42, 130.78, 128.20, 124.45, 123.53, 122.77, 121.88, 121.46, 117.09, 54.52, 29.47, 29.32 p.p.m.