5,7,7,8,10-Penta­bromo-7,8-di­hydro­benzo­cyclo­octene

In the title compound, C₁₂H₇Br₅, the eight-membered ring adopts a boat conformation. The repulsive interactions between the Br atoms affect the conformation of the mol­ecule.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.014 Å
• R factor = 0.043
• wR factor = 0.107
• Data-to-parameter ratio = 18.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



PLAT_360  Alert C Short  C(sp3)-C(sp3) Bond  C(9)   -   C(10)  =       1.42 Ang.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

Because of its unusual physical and chemical properties and partial antiaromaticity, biphenylene have received a great deal of attention. According to expectation, biphenylene has been evidenced to have some specific reactivity. For example, biphenylene was brominated in the presence of pyridine to give a monobromobiphenylene (substitution product) in a yield of 49% and in the absence of the catalyst to give benzo[8]annulene derivatives (ring-opening products) as the main product. However, bromination of biphenylene is tedious and unsatisfactory. The nature of the intermediates and the reaction mechanisms are complicated and some suggested structures are questionable (Cava & Mitchen, 1965; Barton, 1969). Furthermore, it has been observed that biphenylene generally showed low reactivity with bromine at room temperature where substantial amounts of unreacted biphenylene were recovered (Barton et al., 1964; Kidokoro et al., 1982).

A survey of literature on eight-membered rings and fused ones to aromatic molecules shows that these rings are one of the most difficult to prepare, due to their high steric energy and transannular effects (Imai et al., 1999). Eight-membered cyclic compounds are found widely in nature and many biologically active cyclooctanoids natural products (Petasis & Patane, 1992) and synthetic compounds have been studied. Therefore, an X-ray crystal structure determination of (I) shown in the scheme was undertaken to elucidate its molecular conformation.

Fig. 1 shows the conformation and molecular structure of compound (I) with the atomic numbering scheme. In the eight-membered ring, the bonds C7—C8 and C11—C12 are double bonds of 1.32 (1) and 1.30 (1) Å, respectively. The bond lengths and angles in (I) are in accordance with conventional values, except for the bond length C9—C10 [1.42 (1) Å], which is sligthly shortened compared with a typical Csp³—Csp³ bond.

The Br—C—C bond angles are between 103.2 (7) and 119.3 (7)°, with an average value of 112.6 (7)°, which is 115.1 (6)° in exo,exo-9,10,12-tribromotricyclo[6.3.1.02,7]dodeca-2(7),3,5,10-tetraene (Hökelek et al., 1991) and 113.9 (7)° in exo,exo-2,3-endo,endo-5,6-tetrabromobicycloheptane (Hökelek et al., 1998).

As shown in Fig. 2, least-squares planes calculations indicate that the eight-membered ring is folded to form a boat-like conformation [the deviations of atoms C1, C6, C9 and C10 are 0.791 (9), 0.887 (8), 0.610 (9) and 1.081 (11) Å, respectively, from the mean plane through atoms C7, C8, C11 and C12]. The total puckering amplitude parameter Q_T is 1.241 (1) Å (Cremer & Pople, 1975).

There are no unsual short contacts between the molecules and the crystal structure is stabilized by van der Waals interactions. The molecules are stacked on top of one another along the a axis (Fig. 3).

S2. Experimental

Biphenylene (0.5 g, 6.57 mmol) was dissolved in CCl₄ (40 ml) in a flask (100 ml) which was equipped with a reflux condenser. The solution was heated until CCl₄ started to reflux while stirring magnetically. To the refluxing solution, in the dark, was added dropwise bromine (1.59 g, 10 mmol) over 20 min. The reaction progress was monitored by thin-layer chromatography (TLC) or ¹H NMR. The starting material was completely converted to products in 3 h. After cooling to room temperature, the solvent was evaporated providing 2.0 g of crude material. TLC investigation of the residue with hexane elution clearly indicated five spots (R_F 0.76, 0.62, 0.51, 0.42, 0.29) showing five compounds.

TLC was carried out on Merck silica F254 0.255 mm plates, and spots were visualized, where appropriate, by UV fluorescence at 254 nm. Classic column chromatography was performed using Merck 60 (70–230 Mesh) silica. Melting points were determined on a Thomas–Hoover capillary melting points apparatus. Solvents were concentrated at reduced pressure. IR spectra were recorded on an Perkin Elmer 980 instrument. Mass spectra were recorded on VG Zab Spec GC—MS spectrometer under electron-impact (EI) and chemical ionization conditions. NMR spectra were recorded on a Bruker AC 200 L instrument at 200 MHz for ¹H and at 50 MHz for ¹³C NMR.

The obtained product mixture (2.0 g) was chromatographed on silica gel (170 g) eluting with hexane. First, 5,6,8,10-tetrabromobenzo[8]annulene was isolated in a yield of 186 mg (6%) as an oil. Second compenent is 5,7,7,8,10-pentabromo-7,8-dihydrobenzocyclooctene, (I) (110 mg, 2%), colorless crystals: m.p. 393–394 K (dichloromethane/petroleum ether, 1:3). Compound (I): IR (max, KBr/cm^-1): 3040, 2980, 1630, 1610, 1480, 1430, 1330, 1250, 1190, 950, 950, 900, 870, 860, 760. ¹H NMR (200 MHz, CDCl₃): 7.60 (m, 1H, arom.), 7.45 (m, 3H, arom.) 7.45 (s, 1H, H1), 6.65 (d, J 9.03, 1H, H4), 4.66 (d, 1H, H3); ¹³C NMR (50 MHz, CDCl₃): 137.33 (d), 133.64 (d), 136.56 (d), 133.96 (s), 130.67 (d) 130.16 (d), 130.02 (d), 128.73 (d), 121.60 (s), 118.61 (s), 58.43 (d), 64.65 (d); MS (m/z, EI): 57/549/551/553/555, (M+, 3), 467/469/471/473/475 (M+, –Br, 80), 387/389/393 (M+, -2Br, 5), 309/311/313 (M+ -3Br, 41), 230/232 (M+, -4Br, 100), 150 (M+, -5Br, 60); found: C 26.93, H 1.21; C₁₂H₇Br₅ requires C 26.17, H 1.28%.

S3. Refinement

H atoms were placed geometrically and refined using the usual riding model.

Computing details

Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. An ORTEP-3 (Farrugia, 1997) drawing of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. The eight-membered ring of the title compound represents a boat-like conformation.
	Fig. 3. A view of the packing diagram for the title compound.

5,7,7,8,10-Pentabromo-7,8-dihydro-benzocyclooctene

Crystal data

C12H7Br5	F(000) = 1016
Mr = 550.73	Dx = 2.488 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 25 reflections
a = 11.727 (5) Å	θ = 2.6–26.3°
b = 11.250 (5) Å	µ = 13.64 mm^−1
c = 12.104 (5) Å	T = 293 K
β = 112.957 (5)°	Prism, colorless
V = 1470.4 (11) Å^3	0.40 × 0.20 × 0.12 mm
Z = 4

Data collection

Enraf Nonius TurboCAD4 diffractometer	1358 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.057
Graphite monochromator	θmax = 25.6°, θmin = 2.6°
non–profiled ω scans	h = −13→14
Absorption correction: part of the refinement model (ΔF) (SHELXA; Sheldrick, 1998)	k = 0→13
Tmin = 0.047, Tmax = 0.195	l = −14→0
2899 measured reflections	3 standard reflections every 120 min
2766 independent reflections	intensity decay: 4%

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)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.107	H-atom parameters constrained
S = 0.97	w = 1/[σ^2(Fo^2) + (0.0429P)^2] where P = (Fo^2 + 2Fc^2)/3
2766 reflections	(Δ/σ)max < 0.001
154 parameters	Δρmax = 0.69 e Å^−3
1 restraint	Δρmin = −0.72 e Å^−3

Special details

Experimental. Absorption correction details

SHELXA, Sheldrick (1998) I/σ threshold for reflections = 5.0 Δ(U)/λ² = 0.0 Highest even order spherical harmonic = 8 Highest odd order spherical harmonic = 5

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
C3	−0.0111 (12)	0.3204 (9)	0.4856 (11)	0.074 (3)
H3	−0.0729	0.3667	0.4942	0.089*
C4	0.1106 (13)	0.3404 (9)	0.5580 (10)	0.074 (3)
H4	0.1319	0.4000	0.6157	0.089*
C6	0.1738 (9)	0.1818 (7)	0.4584 (8)	0.047 (2)
C8	0.3121 (8)	0.0814 (8)	0.3656 (8)	0.055 (2)
H8	0.3803	0.0312	0.3869	0.066*
C9	0.2635 (9)	0.1225 (8)	0.2394 (8)	0.061 (3)
C5	0.2008 (10)	0.2710 (8)	0.5441 (9)	0.065 (3)
H5	0.2831	0.2845	0.5941	0.078*
C7	0.2744 (7)	0.1043 (7)	0.4532 (7)	0.046 (2)
C10	0.1373 (9)	0.1583 (9)	0.1861 (8)	0.075 (3)
H10	0.1317	0.2260	0.2346	0.090*
C1	0.0489 (8)	0.1632 (8)	0.3830 (8)	0.050 (2)
C12	0.0110 (8)	0.0735 (7)	0.2863 (8)	0.050 (2)
C2	−0.0421 (9)	0.2319 (8)	0.4002 (9)	0.064 (3)
H2	−0.1251	0.2176	0.3532	0.077*
C11	0.0490 (8)	0.0688 (8)	0.1990 (8)	0.055 (2)
H11	0.0205	0.0079	0.1428	0.066*
Br3	0.27169 (11)	−0.01830 (8)	0.13426 (10)	0.0669 (3)
Br4	0.07589 (10)	0.21777 (9)	0.02554 (9)	0.0689 (3)
Br2	0.38092 (10)	0.23950 (8)	0.22461 (9)	0.0640 (3)
Br1	0.37014 (10)	0.03489 (11)	0.60559 (10)	0.0819 (4)
Br5	−0.10453 (10)	−0.04079 (9)	0.29382 (11)	0.0784 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C3	0.098 (10)	0.056 (7)	0.086 (9)	0.028 (6)	0.056 (8)	0.011 (6)
C4	0.101 (10)	0.057 (7)	0.074 (8)	0.006 (7)	0.043 (8)	−0.001 (6)
C6	0.047 (7)	0.050 (5)	0.049 (5)	0.008 (5)	0.026 (5)	0.011 (4)
C8	0.029 (6)	0.072 (6)	0.058 (6)	0.007 (5)	0.011 (5)	0.019 (5)
C9	0.043 (7)	0.090 (7)	0.053 (6)	0.001 (5)	0.022 (5)	0.019 (5)
C5	0.060 (8)	0.069 (7)	0.069 (7)	−0.011 (6)	0.027 (6)	−0.004 (6)
C7	0.021 (5)	0.063 (6)	0.048 (5)	0.008 (4)	0.007 (4)	0.013 (4)
C10	0.053 (8)	0.102 (8)	0.063 (7)	−0.012 (6)	0.016 (6)	0.027 (6)
C1	0.033 (6)	0.063 (6)	0.055 (6)	0.016 (5)	0.018 (5)	0.011 (5)
C12	0.036 (6)	0.052 (6)	0.070 (6)	0.007 (4)	0.028 (5)	0.008 (5)
C2	0.048 (7)	0.075 (7)	0.071 (7)	0.013 (6)	0.024 (6)	0.014 (6)
C11	0.044 (6)	0.060 (6)	0.055 (6)	−0.014 (5)	0.013 (5)	−0.006 (5)
Br3	0.0807 (8)	0.0529 (6)	0.0819 (7)	0.0005 (5)	0.0478 (6)	−0.0078 (5)
Br4	0.0686 (8)	0.0747 (7)	0.0568 (6)	0.0120 (6)	0.0171 (5)	0.0099 (5)
Br2	0.0581 (7)	0.0751 (7)	0.0665 (6)	−0.0239 (5)	0.0326 (5)	−0.0136 (5)
Br1	0.0510 (7)	0.1344 (10)	0.0627 (7)	0.0288 (7)	0.0249 (5)	0.0282 (7)
Br5	0.0522 (7)	0.0874 (8)	0.1031 (9)	−0.0136 (6)	0.0383 (6)	0.0070 (7)

Geometric parameters (Å, º)

C3—C4	1.371 (14)	C9—Br3	2.057 (10)
C3—C2	1.378 (13)	C5—H5	0.9300
C3—H3	0.9300	C7—Br1	1.912 (8)
C4—C5	1.377 (13)	C10—C11	1.496 (12)
C4—H4	0.9300	C10—Br4	1.911 (9)
C6—C5	1.388 (12)	C10—H10	0.9800
C6—C1	1.407 (12)	C1—C2	1.398 (12)
C6—C7	1.488 (11)	C1—C12	1.477 (12)
C8—C7	1.323 (11)	C12—C11	1.298 (11)
C8—C9	1.482 (12)	C12—Br5	1.896 (8)
C8—H8	0.9300	C2—H2	0.9300
C9—C10	1.422 (13)	C11—H11	0.9300
C9—Br2	1.963 (9)
C4—C3—C2	120.1 (10)	C8—C7—C6	131.8 (8)
C4—C3—H3	119.9	C8—C7—Br1	116.1 (6)
C2—C3—H3	119.9	C6—C7—Br1	112.0 (6)
C3—C4—C5	119.2 (10)	C9—C10—C11	113.7 (8)
C3—C4—H4	120.4	C9—C10—Br4	118.3 (7)
C5—C4—H4	120.4	C11—C10—Br4	109.9 (7)
C5—C6—C1	117.9 (8)	C9—C10—H10	104.5
C5—C6—C7	120.1 (9)	C11—C10—H10	104.5
C1—C6—C7	121.8 (8)	Br4—C10—H10	104.5
C7—C8—C9	130.7 (9)	C2—C1—C6	118.9 (9)
C7—C8—H8	114.7	C2—C1—C12	119.0 (9)
C9—C8—H8	114.7	C6—C1—C12	122.1 (8)
C10—C9—C8	118.0 (8)	C11—C12—C1	125.5 (8)
C10—C9—Br2	114.3 (7)	C11—C12—Br5	119.3 (7)
C8—C9—Br2	107.6 (7)	C1—C12—Br5	115.1 (6)
C10—C9—Br3	103.2 (7)	C3—C2—C1	121.2 (10)
C8—C9—Br3	107.8 (6)	C3—C2—H2	119.4
Br2—C9—Br3	104.9 (4)	C1—C2—H2	119.4
C4—C5—C6	122.6 (10)	C12—C11—C10	121.9 (9)
C4—C5—H5	118.7	C12—C11—H11	119.0
C6—C5—H5	118.7	C10—C11—H11	119.0
C2—C3—C4—C5	0.0 (16)	Br2—C9—C10—Br4	49.4 (10)
C7—C8—C9—C10	−24.1 (16)	Br3—C9—C10—Br4	−63.9 (8)
C7—C8—C9—Br2	107.0 (11)	C5—C6—C1—C2	−2.3 (12)
C7—C8—C9—Br3	−140.5 (9)	C7—C6—C1—C2	174.0 (8)
C3—C4—C5—C6	0.7 (15)	C5—C6—C1—C12	177.7 (8)
C1—C6—C5—C4	0.5 (13)	C7—C6—C1—C12	−6.0 (13)
C7—C6—C5—C4	−175.8 (8)	C2—C1—C12—C11	122.9 (10)
C9—C8—C7—C6	−2.4 (18)	C6—C1—C12—C11	−57.1 (13)
C9—C8—C7—Br1	−178.0 (8)	C2—C1—C12—Br5	−56.2 (10)
C5—C6—C7—C8	−123.4 (11)	C6—C1—C12—Br5	123.8 (7)
C1—C6—C7—C8	60.5 (14)	C4—C3—C2—C1	−1.9 (15)
C5—C6—C7—Br1	52.3 (9)	C6—C1—C2—C3	3.0 (13)
C1—C6—C7—Br1	−123.8 (7)	C12—C1—C2—C3	−177.0 (9)
C8—C9—C10—C11	−51.5 (13)	C1—C12—C11—C10	−0.9 (15)
Br2—C9—C10—C11	−179.5 (7)	Br5—C12—C11—C10	178.3 (7)
Br3—C9—C10—C11	67.3 (9)	C9—C10—C11—C12	94.2 (12)
C8—C9—C10—Br4	177.4 (7)	Br4—C10—C11—C12	−130.7 (9)