4,4'-Bibenzocyclo­butene

In the mol­ecule of the title compound, C₁₆H₁₄, the dihedral angles between the planar rings are 1.92 (3) and 0.27 (3)° between the two pairs of fused rings, and 38.00 (4)° between the two six-membered rings.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.050
• wR factor = 0.140
• Data-to-parameter ratio = 15.5

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S1. Comment

Benzocyclobutenes (BCBs) are a family of thermally polymerisable monomers for high-performance polymers, which have been widely used in the microelectronics industry because of their low dielectric constant, low dispersion factor, low water up-take, high thermal and chemical stabilities, and ease of processing (Kirchhoff & Bruza, 1993). Homopolymers and copolymers of aryl bridged bisbenzocyclobutene monomers (bisBCB) also exhibit excellent properties (Corley & Wong, 1992).

In the molecule of the title compound, (I), (Fig. 1), the bond lengths and angles are within normal ranges (Allen et al., 1987). Rings A (C1—C3/C8), B (C3—C8), C (C9—C14) and D (C11/C12/C15/C16) are, of course, planar and the dihedral angles between them are A/B = 1.92 (3)°, C/D = 0.27 (3)° and B/C = 38.00 (4)°.

As can be seen from the packing diagram, (Fig. 2), the molecules are elongated along the c axis and stacked along the b axis.

Related literature

For general backgroud, see: Allen et al. (1987); Kirchhoff & Bruza (1993); Corley & Wong (1992).

S2. Experimental

A mixture of benzocyclobutene-4-boronic acid (29.6 mg, 0.20 mmol), 4-bromobenzocyclobutene (85.0 mg, 0.46 mmol), tetrabutylammonium bromide (6.44 mg, 0.02 mmol) and palladium chloride (2.83 mg, 0.016 mmol) in ethanol (10 ml) was stirred for 1 h under nitrogen atmosphere at room temperature. Potassium carbonate (580 mg, 0.42 mmol) was then added and the mixture was stirred vigorously for 22 h. The reaction mixture was poured into distilled water (15 ml) and then extracted with chloroform (20 ml) three times. The combined organic phase was washed with distilled water (30 ml) and dried over sodium sulfate. Removal of the solvent under reduced pressure gave a grey-white solid, which could be purified by chromatography on silica gel using petroleum ether, as eluent to recover excess 4-bromobenzocyclobutene first, then using a mixture of petroleum ether and toluene (25:1) to afford (I) (yield; 37.0 mg, 90%, m.p. 333 K). Crystals of (I) suitable for X-ray diffraction was obtained by slow evaporation of hexane.

S3. Refinement

H atoms were positioned geometrically, with C—H = 0.93 and 0.97 Å for aromatic and methylene H, respectively, and constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: CAD-4 Software (Enraf–Nonius, 1989); cell refinement: CAD-4 Software; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 2000); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 2. A packing diagram for (I).

4,4'-bibenzocyclobutene

Crystal data

C16H14	F(000) = 440
Mr = 206.27	Dx = 1.192 Mg m^−3
Monoclinic, P21/n	Melting point: 333 K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71073 Å
a = 8.0250 (16) Å	Cell parameters from 25 reflections
b = 11.365 (2) Å	θ = 10–13°
c = 12.850 (3) Å	µ = 0.07 mm^−1
β = 101.19 (3)°	T = 298 K
V = 1149.7 (4) Å^3	Block, colorless
Z = 4	0.30 × 0.20 × 0.20 mm

Data collection

Enraf–Nonius CAD-4 diffractometer	1414 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 26.0°, θmin = 2.4°
ω/2θ scans	h = −9→9
Absorption correction: ψ scan (North et al., 1968)	k = 0→14
Tmin = 0.980, Tmax = 0.987	l = 0→15
2248 measured reflections	3 standard reflections every 200 reflections
2248 independent reflections	intensity decay: none

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)] = 0.050	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.140	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0408P)^2 + 0.3817P] where P = (Fo^2 + 2Fc^2)/3
2248 reflections	(Δ/σ)max < 0.001
145 parameters	Δρmax = 0.14 e Å^−3
0 restraints	Δρmin = −0.13 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
C1	0.0790 (4)	0.9190 (3)	0.31338 (18)	0.0752 (8)
H1A	0.1490	0.9893	0.3212	0.090*
H1B	−0.0403	0.9381	0.2901	0.090*
C2	0.1442 (3)	0.8183 (3)	0.24864 (19)	0.0748 (8)
H2A	0.0580	0.7859	0.1925	0.090*
H2B	0.2470	0.8375	0.2231	0.090*
C3	0.1737 (3)	0.7478 (2)	0.34986 (18)	0.0589 (6)
C4	0.2271 (3)	0.6419 (2)	0.3941 (2)	0.0673 (7)
H4A	0.2675	0.5831	0.3553	0.081*
C5	0.2181 (3)	0.6263 (2)	0.50072 (19)	0.0600 (6)
H5A	0.2547	0.5555	0.5336	0.072*
C6	0.1557 (3)	0.7139 (2)	0.55964 (17)	0.0494 (6)
C7	0.1062 (3)	0.8223 (2)	0.51261 (17)	0.0552 (6)
H7A	0.0685	0.8829	0.5508	0.066*
C8	0.1155 (3)	0.8361 (2)	0.40726 (17)	0.0558 (6)
C9	0.1413 (3)	0.6890 (2)	0.67190 (17)	0.0502 (6)
C10	0.1747 (3)	0.7754 (2)	0.74977 (17)	0.0531 (6)
H10A	0.2084	0.8507	0.7344	0.064*
C11	0.1560 (3)	0.7448 (2)	0.85081 (17)	0.0518 (6)
C12	0.1065 (3)	0.6355 (2)	0.87572 (18)	0.0559 (6)
C13	0.0705 (3)	0.5482 (2)	0.8009 (2)	0.0624 (7)
H13A	0.0351	0.4738	0.8177	0.075*
C14	0.0897 (3)	0.5770 (2)	0.69819 (18)	0.0561 (6)
H14A	0.0675	0.5198	0.6455	0.067*
C15	0.1723 (3)	0.7919 (2)	0.96359 (17)	0.0634 (7)
H15A	0.0934	0.8546	0.9710	0.076*
H15B	0.2874	0.8116	0.9981	0.076*
C16	0.1122 (4)	0.6654 (2)	0.99105 (19)	0.0743 (8)
H16A	0.1963	0.6215	1.0405	0.089*
H16B	0.0023	0.6640	1.0119	0.089*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.091 (2)	0.085 (2)	0.0501 (14)	−0.0114 (16)	0.0156 (14)	0.0022 (14)
C2	0.0746 (18)	0.104 (2)	0.0470 (14)	−0.0247 (16)	0.0143 (13)	−0.0124 (14)
C3	0.0588 (15)	0.0726 (17)	0.0474 (13)	−0.0176 (13)	0.0153 (11)	−0.0137 (12)
C4	0.0708 (17)	0.0742 (18)	0.0616 (16)	−0.0081 (14)	0.0244 (13)	−0.0249 (14)
C5	0.0663 (16)	0.0543 (15)	0.0627 (15)	−0.0014 (12)	0.0207 (12)	−0.0090 (12)
C6	0.0493 (13)	0.0538 (14)	0.0466 (12)	−0.0040 (11)	0.0133 (10)	−0.0033 (11)
C7	0.0649 (15)	0.0566 (14)	0.0475 (13)	−0.0039 (12)	0.0190 (11)	−0.0045 (11)
C8	0.0562 (14)	0.0659 (16)	0.0456 (13)	−0.0089 (12)	0.0103 (11)	−0.0033 (12)
C9	0.0493 (13)	0.0526 (14)	0.0509 (13)	−0.0027 (11)	0.0150 (10)	−0.0007 (11)
C10	0.0583 (14)	0.0491 (13)	0.0538 (14)	−0.0041 (11)	0.0154 (11)	−0.0001 (11)
C11	0.0493 (13)	0.0601 (15)	0.0465 (13)	0.0039 (11)	0.0106 (10)	0.0008 (11)
C12	0.0541 (14)	0.0611 (15)	0.0537 (14)	0.0060 (12)	0.0133 (11)	0.0095 (12)
C13	0.0701 (17)	0.0514 (15)	0.0701 (16)	−0.0004 (12)	0.0243 (13)	0.0117 (13)
C14	0.0597 (15)	0.0515 (14)	0.0588 (14)	−0.0037 (12)	0.0159 (12)	−0.0037 (12)
C15	0.0622 (16)	0.0784 (18)	0.0483 (13)	0.0037 (14)	0.0073 (11)	−0.0027 (13)
C16	0.0791 (19)	0.093 (2)	0.0537 (15)	0.0096 (16)	0.0203 (13)	0.0148 (14)

Geometric parameters (Å, º)

C1—C8	1.514 (3)	C9—C10	1.390 (3)
C1—C2	1.564 (4)	C9—C14	1.401 (3)
C1—H1A	0.9700	C10—C11	1.380 (3)
C1—H1B	0.9700	C10—H10A	0.9300
C2—C3	1.507 (3)	C11—C12	1.361 (3)
C2—H2A	0.9700	C11—C15	1.526 (3)
C2—H2B	0.9700	C12—C13	1.373 (3)
C3—C4	1.364 (4)	C12—C16	1.512 (3)
C3—C8	1.380 (3)	C13—C14	1.397 (3)
C4—C5	1.397 (3)	C13—H13A	0.9300
C4—H4A	0.9300	C14—H14A	0.9300
C5—C6	1.401 (3)	C15—C16	1.578 (4)
C5—H5A	0.9300	C15—H15A	0.9700
C6—C7	1.395 (3)	C15—H15B	0.9700
C6—C9	1.497 (3)	C16—H16A	0.9700
C7—C8	1.379 (3)	C16—H16B	0.9700
C7—H7A	0.9300
C8—C1—C2	86.3 (2)	C10—C9—C14	119.6 (2)
C8—C1—H1A	114.3	C10—C9—C6	121.3 (2)
C2—C1—H1A	114.3	C14—C9—C6	119.1 (2)
C8—C1—H1B	114.3	C11—C10—C9	117.2 (2)
C2—C1—H1B	114.3	C11—C10—H10A	121.4
H1A—C1—H1B	111.4	C9—C10—H10A	121.4
C3—C2—C1	86.72 (18)	C12—C11—C10	122.8 (2)
C3—C2—H2A	114.2	C12—C11—C15	94.11 (19)
C1—C2—H2A	114.2	C10—C11—C15	143.1 (2)
C3—C2—H2B	114.2	C11—C12—C13	121.8 (2)
C1—C2—H2B	114.2	C11—C12—C16	94.1 (2)
H2A—C2—H2B	111.4	C13—C12—C16	144.1 (2)
C4—C3—C8	122.0 (2)	C12—C13—C14	116.5 (2)
C4—C3—C2	144.4 (2)	C12—C13—H13A	121.8
C8—C3—C2	93.5 (2)	C14—C13—H13A	121.8
C3—C4—C5	116.7 (2)	C13—C14—C9	122.2 (2)
C3—C4—H4A	121.6	C13—C14—H14A	118.9
C5—C4—H4A	121.6	C9—C14—H14A	118.9
C4—C5—C6	122.1 (2)	C11—C15—C16	85.38 (19)
C4—C5—H5A	119.0	C11—C15—H15A	114.4
C6—C5—H5A	119.0	C16—C15—H15A	114.4
C7—C6—C5	119.7 (2)	C11—C15—H15B	114.4
C7—C6—C9	121.0 (2)	C16—C15—H15B	114.4
C5—C6—C9	119.3 (2)	H15A—C15—H15B	111.5
C8—C7—C6	117.4 (2)	C12—C16—C15	86.41 (18)
C8—C7—H7A	121.3	C12—C16—H16A	114.3
C6—C7—H7A	121.3	C15—C16—H16A	114.3
C7—C8—C3	122.0 (2)	C12—C16—H16B	114.3
C7—C8—C1	144.5 (2)	C15—C16—H16B	114.3
C3—C8—C1	93.4 (2)	H16A—C16—H16B	111.4
C8—C1—C2—C3	−0.28 (19)	C7—C6—C9—C14	141.2 (2)
C1—C2—C3—C4	178.6 (4)	C5—C6—C9—C14	−38.0 (3)
C1—C2—C3—C8	0.3 (2)	C14—C9—C10—C11	0.5 (3)
C8—C3—C4—C5	0.8 (4)	C6—C9—C10—C11	179.2 (2)
C2—C3—C4—C5	−177.2 (3)	C9—C10—C11—C12	−0.2 (3)
C3—C4—C5—C6	0.7 (4)	C9—C10—C11—C15	179.1 (3)
C4—C5—C6—C7	−2.4 (4)	C10—C11—C12—C13	−0.6 (4)
C4—C5—C6—C9	176.9 (2)	C15—C11—C12—C13	179.9 (2)
C5—C6—C7—C8	2.5 (3)	C10—C11—C12—C16	−179.6 (2)
C9—C6—C7—C8	−176.8 (2)	C15—C11—C12—C16	0.8 (2)
C6—C7—C8—C3	−1.0 (4)	C11—C12—C13—C14	0.9 (4)
C6—C7—C8—C1	176.4 (3)	C16—C12—C13—C14	179.3 (3)
C4—C3—C8—C7	−0.6 (4)	C12—C13—C14—C9	−0.6 (4)
C2—C3—C8—C7	178.2 (2)	C10—C9—C14—C13	−0.1 (4)
C4—C3—C8—C1	−179.1 (2)	C6—C9—C14—C13	−178.8 (2)
C2—C3—C8—C1	−0.3 (2)	C12—C11—C15—C16	−0.8 (2)
C2—C1—C8—C7	−177.5 (3)	C10—C11—C15—C16	179.8 (3)
C2—C1—C8—C3	0.3 (2)	C11—C12—C16—C15	−0.8 (2)
C7—C6—C9—C10	−37.5 (3)	C13—C12—C16—C15	−179.4 (4)
C5—C6—C9—C10	143.3 (2)	C11—C15—C16—C12	0.73 (18)