The `cyclo­phene' [2.2.2](1,2,4)cyclo­phan-9-ene

In the title compound, C₁₈H₁₆, the [2.2]paracyclo­phane geometry is restrained to a considerable extent despite the introduction of the extra C=C bridge; typical paracyclo­phane features, such as the elongated C-C bridges, are still observed. However, the bridgehead atoms of the C=C bridge are forced into unusually close proximity [2.657 (3) Å], which in turn causes the rings to be rotated to an inter­planar angle of 13.7 (2)°. The packing involves hexa­gonally close-packed layers of mol­ecules parallel to the xy plane, corresponding to the known `7,11' pattern of paracyclo­phanes, but without significant short inter­molecular contacts.

S1. Comment

In contrast to to the [2_n]cyclophanes with saturated bridges – from [2₂]paracyclophane (review article: Hopf & Kleinschroth, 1982) to superphane ([2₆]paracyclophane; review article: Gleiter & Roers, 2004) – relatively little is known about the chemical behavior and the structural properties of cyclophanes with unsaturated bridges (`cyclophenes'). We report here the preparation and the structural properties of [2.2.2](1,2,4)cyclophan-9-ene, (III), a triply bridged cyclophane in which one of the ethano bridges of its saturated analogue has been replaced by a double bond. The unsaturated analogue of superphane, superphene, a hydrocarbon with six adjacent unsaturated bridges, is so far unknown. A search of the Cambridge Structural Database (Allen, 2002) revealed no other cyclophene of the [2.2.2](1,2,4) type.

The molecule of (III) is shown in Fig. 1; selected molecular dimensions are presented in Table 1. The molecule may be regarded as a derivative of [2.2]paracyclophane (bridgehead atoms C3, C6, C13 and C16); as we have previously noted in such derivatives with extra bridges (Bondarenko et al., 2007, and references therein) the molecular geometry is changed surprisingly little by the extra bridge. Typical features of [2.2]paracyclophanes are elongated single bonds in the bridges, widened sp³ angles at the bridge atoms, narrowed sp² angles in the six-membered rings at the bridgehead atoms, and flattened boat conformations of the rings, with the bridgehead atoms displaced by ca 0.10–0.15 Å from the mean plane of the other four atoms towards the centre of the molecule. All these features are observed in (III) (Table 1), except that the deviations of the bridgehead atoms are slightly smaller [0.111 (3) Å for C3, 0.136 (3) Å for C6, 0.146 (4) Å for C13 and 0.115 (4) Å for C16].

However, whereas the rings in normal [2.2]paracyclophanes are parallel, those in (III) are significantly rotated, with an interplanar angle of 13.7 (2)°; this is also an effect that we have noted before (Bondarenko et al., 2007, and references therein), and is presumably connected with the extra bridge C9═C10. The bridge is not elongated with respect to normal C═C distances, but the angles at the bridge atoms are significantly narrower than ideal sp² angles. This leads to an extremely short contact of 2.657 (3) Å between the formally nonbonded atoms C8 and C11, whereas the ring rotation causes atoms C4 and C5 to be farther than usual (> 3.2 Å) from their counterparts (Table 2).

The crystal packing involves layers of molecules parallel to the xy plane, with four layers per cell at z ≈ 1/8, 3/8, 5/8 and 7/8. One such layer is shown in Fig. 2. The molecules are arranged in a hexagonally close-packed pattern; connecting the centroids of adjacent molecules, which are related by the b glide planes, forms a rhombus with sides of ca 7.0 Å and angles of 66 and 113°. The approximately equidimensional nature of the molecules of simple [2.2]paracyclophane derivatives often leads to such layer structures, in which the two cell constants associated with the layer are, as here, often ca 7 and 11 Å. We have called this the `7,11'-packing pattern (El Shaieb et al., 2003; Jones et al., 2007). In many cases, adjacent molecules are connected by C—H···π contacts, sometimes extremely short, but in (III) there are no H···(C9═C10) contacts shorter than 3.17 Å and no H···(ring centroid) contacts greater than 3.34 Å.

Related literature

For related literature, see: Allen (2002); Bondarenko et al. (2007); El Shaieb, Narayanan, Hopf, Dix, Fischer, Jones, Ernst & Ibrom (2003); Gleiter & Roers (2004); Hopf & Kleinschroth (1982); Jones et al. (2007).

S2. Experimental

For the preparation of the bis-tosylhydrazone (II) of the pseudo-geminal dialdehyde (I) (Bondarenko et al., 2007, and references therein), a solution of (I) (1.5 g, 5.68 mmol) and p-toluenesulfonic acid hydrazide (3.0 g, 16.12 mmol) in anhydrous tetrahydrofuran (250 ml) was refluxed for 2 h in the presence of a trace of p-toluenesulfonic acid. After cooling to room temperature, the solvent was removed in vacuo and the raw product purified by plate chromatography on silica gel with dichloromethane/ethyl acetate (98:2 v/v). After recrystallization from dichloromethane/ethanol, (II) (3.13 g, 92%) was obtained as colourless needles [m.p. 467 K (decomposition)]. Analysis calculated for C₃₂H₃₂O₄N₄S₂ (600.76): C 63.98, H 5.36%; found: C 62.94, H 4.98%.

For the preparation of (III), a solution of (II) (3.0 g, 5.0 mmol) and sodium methoxide (3.0 g, 93 mmol) in diglyme (150 ml) was heated under reflux for 3 h. After cooling to room temperature, water (200 ml) was added, and the reaction mixture was extracted with ether. The organic phase was separated and dried (calcium chloride), the solvent was removed by rotary evaporation, and the remainder was purified by plate chromatography on silica gel with tetrachloromethane/dichloromethane (9:1 v/v). After recrystallization from dichloromethane/ethanol, (III) (0.85 g, 73%) was obtained as colourless plates (m.p. 430–431 K). ¹H NMR (400 MHz, CD₂Cl₂, int. TMS): δ 7.24 (s, 2H, 9-H), 6.39 (dd, J_o = 7.9 Hz, J_m = 2.1 Hz, 2H, 5-H), 6.33 (d, J_o = 7.9 Hz, 2H, 4-H), 6.23 (d, J_m = 2.1 Hz, 2H, 7-H), 3.05 (m, 4H, ethano bridge), 2.93 (m, 2H, ethano bridge), 2.61 (m, 2H, ethano bridge); ¹³C NMR (100.6 MHz, CD₂Cl₂): δ 141.98, 141.45, 139.60 (3 × s, quart. C), 139.21, 138.21, 133.47, 130.82 (4 × s, Ar—C, –HC═CH–), 35.42, 34.29 (t, ethano bridges). Analysis calculated for C₁₈H₁₆ (232.33): C 93.06, H 6.94%; found: C 93.16, H 6.85%. Single crystals were obtained from cyclohexane. Additional spectroscopic data for (II) and (III) are given in the deposited material.

S3. Refinement

H-atoms positions were calculated, after which the H atoms were refined using a riding model with C—H distances of 0.95 Å for sp² and 0.99 Å for sp³ C atoms. U_iso(H) values were fixed at 1.2U_eq of the parent C atoms. There is no significant residual electron density that might suggest disorder of the bridges. A rigid-body libration correction (Schomaker & Trueblood, 1968) gave an acceptable R_lib of 0.062 and bond-length corrections of 0.005–0.006 Å; corrected bond lengths are given in the deposited material, but uncorrected values are used in Table 1 and the Comment section. [Please clarify; values in Table 1 ARE the values in the deposited material; should this read Table 2?]

Computing details

Data collection: DIF4 (Stoe & Cie, 1992); cell refinement: DIF4 (Stoe & Cie, 1992); data reduction: REDU4 (Stoe & Cie, 1992); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1994); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

Figures

	Fig. 1. The molecule of (III). Displacement ellipsoids represent 30% probability levels.
	Fig. 2. The packing of (III), viewed parallel to the z axis in the region z ≈ 1/8.

[2.2.2](1,2,4)cyclophan-9-ene

Crystal data

C18H16	Dx = 1.274 Mg m^−3
Mr = 232.31	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 50 reflections
a = 7.6402 (15) Å	θ = 10–11.5°
b = 11.775 (2) Å	µ = 0.07 mm^−1
c = 26.927 (5) Å	T = 153 K
V = 2422.4 (8) Å^3	Tablet, colourless
Z = 8	0.7 × 0.5 × 0.25 mm
F(000) = 992

Data collection

Stoe STADI-4 diffractometer	Rint = 0.059
Radiation source: fine-focus sealed tube	θmax = 25.1°, θmin = 3.0°
Graphite monochromator	h = −9→0
ω/θ scans	k = −14→14
4154 measured reflections	l = 0→32
2139 independent reflections	3 standard reflections every 60 min
1446 reflections with I > 2σ(I)	intensity decay: 5%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.054	H-atom parameters constrained
wR(F^2) = 0.150	w = 1/[σ^2(Fo^2) + (0.0544P)^2 + 0.4953P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max < 0.001
2139 reflections	Δρmax = 0.23 e Å^−3
164 parameters	Δρmin = −0.24 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0042 (9)

Special details

Experimental. Spectroscopic data for bis-tosylhydrazone (II): IR (KBr): ~ν = 3180 (m), 2920 (m), 2840 (m), 1430 (m), 1360 (m), 1320 (m), 1160 (s), 1090 cm^-1 (m); MS (70 eV, EI): m/z (%) = 416 [M⁺—NHTs] (1), 278 (91), 246 (40), 232 (71), 217 (52), 202 (47), 172 (49), 155 (71), 139 (100), 123 (76), 108 (48), 91 (89).

Additional spectroscopic data for [2.2.2](1,2,4)cyclophan-9-ene (III): IR (KBr): ~ν = 2950 (w), 2920 (m), 2880 (w), 2840 (m), 1480 (m), 1430 (m), 1395 (m), 920 (m), 815 (m), 730 cm^-1 (s); UV (acetonitrile): λ_max (lg ε) = 202 (3.30), 220 nm (3.11); MS (70 eV, EI): m/z (%) = 232 [M⁺] (100), 217 (88), 204 (90), 189 (50), 178 (23), 165 (25), 154 (26), 141 (57), 128 (48), 115 (39), 101 (46), 95 (32), 89 (25).

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.

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

4.9418 (0.0057) x + 6.0219 (0.0160) y - 15.2341 (0.0334) z = 2.3993 (0.0230)

* 0.0258 (0.0012) C4 * -0.0261 (0.0012) C5 * 0.0257 (0.0012) C7 * -0.0254 (0.0012) C8 - 0.1110 (0.0034) C3 - 0.1356 (0.0035) C6

Rms deviation of fitted atoms = 0.0258

6.1617 (0.0046) x + 5.0281 (0.0165) y - 11.0117 (0.0372) z = 0.9379 (0.0239)

Angle to previous plane (with approximate e.s.d.) = 13.74 (0.19)

* 0.0282 (0.0012) C11 * -0.0284 (0.0012) C12 * 0.0285 (0.0012) C14 * -0.0284 (0.0012) C15 0.1457 (0.0036) C13 0.1148 (0.0037) C16

Rms deviation of fitted atoms = 0.0284

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	0.4439 (4)	0.4984 (2)	0.33019 (9)	0.0520 (7)
H1A	0.3450	0.4850	0.3072	0.062*
H1B	0.4872	0.4235	0.3415	0.062*
C2	0.5954 (4)	0.5619 (2)	0.30150 (10)	0.0529 (7)
H2A	0.7012	0.5134	0.3013	0.063*
H2B	0.5592	0.5739	0.2666	0.063*
C3	0.6403 (3)	0.6755 (2)	0.32451 (8)	0.0408 (6)
C4	0.7703 (3)	0.6831 (2)	0.36072 (9)	0.0468 (7)
H4	0.8631	0.6294	0.3610	0.056*
C5	0.7654 (4)	0.7678 (2)	0.39603 (9)	0.0489 (7)
H5	0.8510	0.7690	0.4216	0.059*
C6	0.6374 (4)	0.8515 (2)	0.39475 (9)	0.0434 (6)
C7	0.5338 (3)	0.8570 (2)	0.35276 (8)	0.0411 (6)
H7	0.4655	0.9231	0.3469	0.049*
C8	0.5273 (3)	0.7675 (2)	0.31860 (8)	0.0378 (6)
C9	0.3577 (4)	0.7523 (2)	0.29159 (9)	0.0480 (7)
H9	0.3411	0.7788	0.2586	0.058*
C10	0.2314 (4)	0.6994 (2)	0.31666 (9)	0.0479 (7)
H10	0.1191	0.6867	0.3026	0.057*
C11	0.2754 (3)	0.6611 (2)	0.36823 (8)	0.0400 (6)
C12	0.2670 (3)	0.7420 (2)	0.40560 (8)	0.0401 (6)
H12	0.1861	0.8029	0.4027	0.048*
C13	0.3745 (3)	0.7358 (2)	0.44710 (8)	0.0410 (6)
C14	0.4563 (3)	0.6321 (2)	0.45617 (9)	0.0450 (7)
H14	0.5144	0.6199	0.4869	0.054*
C15	0.4538 (4)	0.5468 (2)	0.42101 (9)	0.0457 (7)
H15	0.5036	0.4749	0.4287	0.055*
C16	0.3793 (3)	0.5646 (2)	0.37445 (9)	0.0410 (6)
C17	0.4362 (4)	0.8437 (2)	0.47209 (9)	0.0539 (7)
H17A	0.4859	0.8242	0.5050	0.065*
H17B	0.3340	0.8937	0.4777	0.065*
C18	0.5780 (4)	0.9112 (2)	0.44136 (9)	0.0563 (8)
H18A	0.5292	0.9862	0.4322	0.068*
H18B	0.6812	0.9247	0.4628	0.068*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0636 (18)	0.0350 (13)	0.0573 (16)	−0.0064 (15)	0.0039 (15)	−0.0013 (12)
C2	0.0670 (19)	0.0408 (14)	0.0509 (14)	0.0051 (15)	0.0134 (14)	−0.0006 (12)
C3	0.0450 (15)	0.0381 (14)	0.0394 (13)	−0.0023 (13)	0.0111 (12)	0.0061 (11)
C4	0.0333 (14)	0.0469 (15)	0.0603 (15)	0.0011 (13)	0.0115 (13)	0.0169 (13)
C5	0.0386 (15)	0.0567 (17)	0.0515 (14)	−0.0142 (14)	−0.0051 (12)	0.0140 (14)
C6	0.0446 (15)	0.0385 (14)	0.0471 (14)	−0.0137 (13)	−0.0004 (12)	0.0043 (12)
C7	0.0477 (16)	0.0333 (13)	0.0425 (13)	−0.0039 (12)	0.0004 (12)	0.0071 (11)
C8	0.0449 (14)	0.0371 (14)	0.0314 (11)	−0.0035 (12)	0.0041 (10)	0.0066 (10)
C9	0.0624 (18)	0.0438 (14)	0.0378 (13)	0.0061 (15)	−0.0071 (13)	−0.0010 (12)
C10	0.0436 (15)	0.0493 (15)	0.0508 (14)	0.0021 (14)	−0.0088 (13)	−0.0077 (13)
C11	0.0325 (14)	0.0403 (14)	0.0472 (14)	−0.0043 (12)	0.0001 (11)	0.0000 (12)
C12	0.0313 (13)	0.0432 (14)	0.0457 (13)	0.0028 (12)	0.0069 (11)	−0.0003 (11)
C13	0.0395 (14)	0.0473 (15)	0.0361 (12)	−0.0030 (13)	0.0075 (11)	0.0006 (11)
C14	0.0454 (16)	0.0528 (16)	0.0368 (13)	−0.0040 (14)	0.0027 (12)	0.0152 (12)
C15	0.0495 (16)	0.0356 (13)	0.0521 (14)	−0.0007 (13)	0.0088 (13)	0.0137 (12)
C16	0.0427 (15)	0.0321 (12)	0.0480 (14)	−0.0087 (12)	0.0034 (12)	0.0036 (11)
C17	0.0610 (19)	0.0567 (17)	0.0440 (14)	−0.0029 (16)	0.0023 (14)	−0.0099 (13)
C18	0.068 (2)	0.0504 (16)	0.0506 (15)	−0.0175 (16)	−0.0066 (15)	−0.0068 (13)

Geometric parameters (Å, º)

C1—C16	1.508 (3)	C9—H9	0.9500
C1—C2	1.580 (4)	C10—C11	1.498 (3)
C1—H1A	0.9900	C10—H10	0.9500
C1—H1B	0.9900	C11—C12	1.387 (3)
C2—C3	1.513 (3)	C11—C16	1.395 (3)
C2—H2A	0.9900	C12—C13	1.389 (3)
C2—H2B	0.9900	C12—H12	0.9500
C3—C8	1.394 (3)	C13—C14	1.393 (4)
C3—C4	1.395 (3)	C13—C17	1.513 (3)
C4—C5	1.379 (4)	C14—C15	1.380 (3)
C4—H4	0.9500	C14—H14	0.9500
C5—C6	1.389 (4)	C15—C16	1.393 (3)
C5—H5	0.9500	C15—H15	0.9500
C6—C7	1.381 (3)	C17—C18	1.578 (4)
C6—C18	1.508 (3)	C17—H17A	0.9900
C7—C8	1.400 (3)	C17—H17B	0.9900
C7—H7	0.9500	C18—H18A	0.9900
C8—C9	1.497 (4)	C18—H18B	0.9900
C9—C10	1.332 (4)
C16—C1—C2	112.4 (2)	C9—C10—C11	116.6 (2)
C16—C1—H1A	109.1	C9—C10—H10	121.7
C2—C1—H1A	109.1	C11—C10—H10	121.7
C16—C1—H1B	109.1	C12—C11—C16	119.9 (2)
C2—C1—H1B	109.1	C12—C11—C10	117.0 (2)
H1A—C1—H1B	107.9	C16—C11—C10	119.0 (2)
C3—C2—C1	112.6 (2)	C11—C12—C13	121.3 (2)
C3—C2—H2A	109.1	C11—C12—H12	119.3
C1—C2—H2A	109.1	C13—C12—H12	119.3
C3—C2—H2B	109.1	C12—C13—C14	116.9 (2)
C1—C2—H2B	109.1	C12—C13—C17	119.9 (2)
H2A—C2—H2B	107.8	C14—C13—C17	121.2 (2)
C8—C3—C4	118.1 (2)	C15—C14—C13	120.8 (2)
C8—C3—C2	120.0 (2)	C15—C14—H14	119.6
C4—C3—C2	120.3 (2)	C13—C14—H14	119.6
C5—C4—C3	120.6 (2)	C14—C15—C16	120.8 (2)
C5—C4—H4	119.7	C14—C15—H15	119.6
C3—C4—H4	119.7	C16—C15—H15	119.6
C4—C5—C6	121.0 (2)	C15—C16—C11	117.6 (2)
C4—C5—H5	119.5	C15—C16—C1	119.9 (2)
C6—C5—H5	119.5	C11—C16—C1	120.8 (2)
C7—C6—C5	117.2 (2)	C13—C17—C18	113.8 (2)
C7—C6—C18	119.1 (2)	C13—C17—H17A	108.8
C5—C6—C18	121.4 (2)	C18—C17—H17A	108.8
C6—C7—C8	121.5 (2)	C13—C17—H17B	108.8
C6—C7—H7	119.2	C18—C17—H17B	108.8
C8—C7—H7	119.2	H17A—C17—H17B	107.7
C3—C8—C7	119.2 (2)	C6—C18—C17	114.0 (2)
C3—C8—C9	119.9 (2)	C6—C18—H18A	108.7
C7—C8—C9	116.1 (2)	C17—C18—H18A	108.7
C10—C9—C8	115.9 (2)	C6—C18—H18B	108.7
C10—C9—H9	122.1	C17—C18—H18B	108.7
C8—C9—H9	122.1	H18A—C18—H18B	107.6
C16—C1—C2—C3	−0.6 (3)	C16—C11—C12—C13	7.1 (4)
C1—C2—C3—C8	−73.9 (3)	C10—C11—C12—C13	−149.8 (2)
C1—C2—C3—C4	91.2 (3)	C11—C12—C13—C14	−16.3 (3)
C8—C3—C4—C5	12.9 (3)	C11—C12—C13—C17	147.7 (3)
C2—C3—C4—C5	−152.4 (2)	C12—C13—C14—C15	10.7 (4)
C3—C4—C5—C6	−3.9 (4)	C17—C13—C14—C15	−153.1 (2)
C4—C5—C6—C7	−10.1 (3)	C13—C14—C15—C16	4.1 (4)
C4—C5—C6—C18	152.8 (2)	C14—C15—C16—C11	−13.5 (4)
C5—C6—C7—C8	15.2 (4)	C14—C15—C16—C1	152.3 (2)
C18—C6—C7—C8	−148.2 (2)	C12—C11—C16—C15	7.9 (4)
C4—C3—C8—C7	−7.9 (3)	C10—C11—C16—C15	164.4 (2)
C2—C3—C8—C7	157.5 (2)	C12—C11—C16—C1	−157.7 (2)
C4—C3—C8—C9	−162.5 (2)	C10—C11—C16—C1	−1.1 (4)
C2—C3—C8—C9	2.9 (3)	C2—C1—C16—C15	−91.6 (3)
C6—C7—C8—C3	−6.3 (4)	C2—C1—C16—C11	73.7 (3)
C6—C7—C8—C9	149.3 (2)	C12—C13—C17—C18	−72.1 (3)
C3—C8—C9—C10	75.8 (3)	C14—C13—C17—C18	91.2 (3)
C7—C8—C9—C10	−79.5 (3)	C7—C6—C18—C17	80.0 (3)
C8—C9—C10—C11	−0.5 (3)	C5—C6—C18—C17	−82.7 (3)
C9—C10—C11—C12	81.1 (3)	C13—C17—C18—C6	−4.7 (3)
C9—C10—C11—C16	−76.1 (3)