Acta Cryst. (2009). E65, o528 [ doi:10.1107/S1600536809002475 ]
In the title compound, C20H16Br4, both vinylic substituents were introduced by a Corey-Fuchs reaction using 4,12-diformyl[2.2]paracyclophane as starting material. The title compound may be used as a valuable precursor for the synthesis of diethynyl[2.2]paracyclophane. The title molecule is centrosymmetric with a crystallographic center of inversion between the centers of the two phenyl rings. A strong tilting is observed with an interplanar angle between the best aromatic plane and the vinyl plane of 49.4 (5)°. No significant intermolecular interactions are found in the crystal.
PPh3 (4.20 g, 16.0 mmol), CBr4 (5.31 g, 16.0 mmol) and zinc dust (1.05 g, 16.0 mmol) are placed in a Schlenk tube and CH2Cl2 (45 ml) is added slowly. The mixture is stirred at room temperature for 28 h. Then, 1 b (1.05 g, 4.00 mmol), dissolved in CH2Cl2 (20 ml), is added and stirring is continued for 2 h. The reaction mixture is extracted with three 50 ml portions of pentane. CH2Cl2 is added when the reaction mixture became too viscous for further extractions. The extracts are filtered and evaporated under reduced pressure. The crude product was purified by column chromatography on silica gel with CH2Cl2/petroleum ether (1:1). Slow evaporation afforded white crystals of 2 b (Yield: 94%). mp 183°C, 1H NMR (CDCl3): 3.00 (m, 7H, CH2), 3.24 (m, 1H, CH2), 6.43 (d,2H, J = 8.2 Hz, Haromatic), 6.59 (d, 2H, J = 2.1 Hz, Haromatic), 6.65 (dd, 2H, J = 8.2 Hz, J = 2.1 Hz, Haromatic), 7.43(s, 2H, CH=CBr2) p.p.m.. 13C{1H}NMR (CDCl3): 34.9, 35.4 (C-1, C-2, C-9, C-10), 90.5 (C-18,C-20), 130.5, 134.0, 135.7, 135.8 (C-5, C-7, C-8, C-12, C-13, C-15, C-16,C-17), 136.2 (C-4, C-16), 138.1, 139.3 (C-3, C-6, C-11, C-14) p.p.m.. UV-vis (CH2Cl2)[lmax nm (e)]: 229 (57544 M-1.cm-1),266 (20417 M-1.cm-1). Anal. Calcd for C20H16Br4:C, 41.71, H, 2.80, Found: C, 41.63, H, 2.71.(Clément et al., 2007b).
Refinement was accomplished by full-matrix least-squares methods (based on Fo2, SHELXL97); anisotropic thermal parameters for all non-H atoms in the final cycles; hydrogen atoms were placed in calculated positions and refined using a riding model with Uiso(H) = 1.2 Ueq(C).
Data collection: SMART (Bruker, 2001); cell refinement: SAINT-Plus (Bruker, 2001); data reduction: SAINT-Plus (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).
![[Figure 1]](./im2094fig1thm.gif)
| Fig. 1. ORTEP plotof 2b with 30% probability level. |
![[Figure 2]](./im2094fig2thm.gif)
| Fig. 2. The formation of the title compound. |
| C20H16Br4 | Dx = 2.048 Mg m−3 |
| Mr = 575.97 | Melting point: 456 K |
| Orthorhombic, Pbca | Mo Kα radiation, λ = 0.71073 Å |
| Hall symbol: -P 2ac 2ab | Cell parameters from 1766 reflections |
| a = 12.155 (1) Å | θ = 2.2–27.0° |
| b = 8.3819 (9) Å | µ = 8.62 mm−1 |
| c = 18.335 (2) Å | T = 173 K |
| V = 1867.9 (3) Å3 | Irregular, white |
| Z = 4 | 0.30 × 0.20 × 0.10 mm |
| F(000) = 1104 |
| Bruker APEX CCD diffractometer | 2043 independent reflections |
| Radiation source: fine-focus sealed tube | 1766 reflections with I > 2σ(I) |
| graphite | Rint = 0.045 |
| CCD scans | θmax = 27.0°, θmin = 2.2° |
| Absorption correction: multi-scan (SADABS; Bruker, 1999) | h = −15→15 |
| Tmin = 0.141, Tmax = 0.418 | k = −10→10 |
| 16030 measured reflections | l = −23→23 |
| Refinement on F2 | Primary atom site location: structure-invariant direct methods |
| Least-squares matrix: full | Secondary atom site location: difference Fourier map |
| R[F2 > 2σ(F2)] = 0.032 | Hydrogen site location: inferred from neighbouring sites |
| wR(F2) = 0.073 | H-atom parameters constrained |
| S = 1.08 | w = 1/[σ2(Fo2) + (0.0298P)2 + 3.2824P] where P = (Fo2 + 2Fc2)/3 |
| 2043 reflections | (Δ/σ)max = 0.001 |
| 109 parameters | Δρmax = 0.84 e Å−3 |
| 0 restraints | Δρmin = −0.60 e Å−3 |
| C20H16Br4 | V = 1867.9 (3) Å3 |
| Mr = 575.97 | Z = 4 |
| Orthorhombic, Pbca | Mo Kα radiation |
| a = 12.155 (1) Å | µ = 8.62 mm−1 |
| b = 8.3819 (9) Å | T = 173 K |
| c = 18.335 (2) Å | 0.30 × 0.20 × 0.10 mm |
| Bruker APEX CCD diffractometer | 2043 independent reflections |
| Absorption correction: multi-scan (SADABS; Bruker, 1999) | 1766 reflections with I > 2σ(I) |
| Tmin = 0.141, Tmax = 0.418 | Rint = 0.045 |
| 16030 measured reflections | θmax = 27.0° |
| R[F2 > 2σ(F2)] = 0.032 | H-atom parameters constrained |
| wR(F2) = 0.073 | Δρmax = 0.84 e Å−3 |
| S = 1.08 | Δρmin = −0.60 e Å−3 |
| 2043 reflections | Absolute structure: ? |
| 109 parameters | Flack parameter: ? |
| 0 restraints | Rogers parameter: ? |
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. |
| x | y | z | Uiso*/Ueq | ||
| Br1 | 0.94392 (3) | 0.12568 (5) | 0.72066 (2) | 0.03823 (13) | |
| Br2 | 1.18942 (3) | 0.01277 (4) | 0.70021 (2) | 0.03403 (12) | |
| C1 | 1.0695 (3) | 0.1284 (4) | 0.66105 (19) | 0.0223 (7) | |
| C2 | 1.0750 (3) | 0.1954 (4) | 0.59555 (18) | 0.0216 (7) | |
| H2 | 1.1423 | 0.1819 | 0.5699 | 0.026* | |
| C3 | 0.9893 (3) | 0.2882 (4) | 0.55781 (18) | 0.0198 (6) | |
| C4 | 0.9745 (3) | 0.2705 (4) | 0.48219 (18) | 0.0215 (7) | |
| C5 | 0.8859 (3) | 0.3511 (4) | 0.45039 (19) | 0.0250 (7) | |
| H5 | 0.8626 | 0.3226 | 0.4027 | 0.030* | |
| C6 | 0.8316 (3) | 0.4717 (4) | 0.4873 (2) | 0.0241 (7) | |
| H6 | 0.7720 | 0.5255 | 0.4645 | 0.029* | |
| C7 | 0.8632 (3) | 0.5151 (4) | 0.55752 (19) | 0.0227 (7) | |
| C8 | 0.9336 (3) | 0.4115 (4) | 0.59427 (18) | 0.0213 (7) | |
| H8 | 0.9442 | 0.4246 | 0.6453 | 0.026* | |
| C9 | 0.8418 (3) | 0.6819 (4) | 0.5856 (2) | 0.0280 (8) | |
| H9A | 0.8312 | 0.6778 | 0.6391 | 0.034* | |
| H9B | 0.7729 | 0.7228 | 0.5636 | 0.034* | |
| C10 | 1.0610 (3) | 0.1987 (4) | 0.43258 (19) | 0.0263 (7) | |
| H10A | 1.0256 | 0.1650 | 0.3864 | 0.032* | |
| H10B | 1.0918 | 0.1023 | 0.4562 | 0.032* |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Br1 | 0.0365 (2) | 0.0460 (2) | 0.0321 (2) | 0.01147 (17) | 0.01440 (17) | 0.01208 (17) |
| Br2 | 0.0273 (2) | 0.0414 (2) | 0.0335 (2) | 0.00426 (16) | −0.00318 (15) | 0.01310 (16) |
| C1 | 0.0172 (15) | 0.0229 (15) | 0.0267 (17) | 0.0017 (13) | −0.0003 (13) | −0.0005 (13) |
| C2 | 0.0174 (15) | 0.0218 (15) | 0.0256 (17) | 0.0000 (12) | 0.0026 (13) | 0.0015 (13) |
| C3 | 0.0163 (15) | 0.0181 (15) | 0.0251 (17) | −0.0045 (12) | 0.0000 (13) | 0.0023 (12) |
| C4 | 0.0238 (17) | 0.0148 (14) | 0.0260 (17) | −0.0054 (12) | −0.0006 (13) | −0.0006 (12) |
| C5 | 0.0257 (17) | 0.0270 (17) | 0.0223 (18) | −0.0090 (14) | −0.0035 (14) | 0.0024 (13) |
| C6 | 0.0173 (16) | 0.0240 (16) | 0.0309 (19) | −0.0051 (13) | −0.0015 (14) | 0.0065 (14) |
| C7 | 0.0182 (16) | 0.0245 (16) | 0.0254 (18) | −0.0033 (13) | 0.0047 (13) | 0.0034 (13) |
| C8 | 0.0198 (16) | 0.0228 (16) | 0.0212 (16) | −0.0022 (13) | 0.0011 (13) | 0.0024 (12) |
| C9 | 0.0298 (18) | 0.0275 (17) | 0.0266 (19) | 0.0080 (14) | 0.0060 (15) | 0.0040 (14) |
| C10 | 0.0342 (19) | 0.0224 (15) | 0.0223 (17) | −0.0003 (14) | −0.0004 (15) | −0.0027 (13) |
| Br1—C1 | 1.878 (3) | C6—C7 | 1.392 (5) |
| Br2—C1 | 1.892 (3) | C6—H6 | 0.9500 |
| C1—C2 | 1.328 (5) | C7—C8 | 1.392 (4) |
| C2—C3 | 1.473 (4) | C7—C9 | 1.512 (5) |
| C2—H2 | 0.9500 | C8—H8 | 0.9500 |
| C3—C8 | 1.405 (4) | C9—C10i | 1.584 (5) |
| C3—C4 | 1.406 (5) | C9—H9A | 0.9900 |
| C4—C5 | 1.399 (5) | C9—H9B | 0.9900 |
| C4—C10 | 1.515 (5) | C10—C9i | 1.584 (5) |
| C5—C6 | 1.385 (5) | C10—H10A | 0.9900 |
| C5—H5 | 0.9500 | C10—H10B | 0.9900 |
| C2—C1—Br1 | 124.9 (2) | C6—C7—C8 | 117.0 (3) |
| C2—C1—Br2 | 121.4 (2) | C6—C7—C9 | 120.5 (3) |
| Br1—C1—Br2 | 113.53 (17) | C8—C7—C9 | 121.2 (3) |
| C1—C2—C3 | 127.8 (3) | C7—C8—C3 | 121.6 (3) |
| C1—C2—H2 | 116.1 | C7—C8—H8 | 119.2 |
| C3—C2—H2 | 116.1 | C3—C8—H8 | 119.2 |
| C8—C3—C4 | 119.0 (3) | C7—C9—C10i | 112.6 (3) |
| C8—C3—C2 | 120.4 (3) | C7—C9—H9A | 109.1 |
| C4—C3—C2 | 119.9 (3) | C10i—C9—H9A | 109.1 |
| C5—C4—C3 | 117.3 (3) | C7—C9—H9B | 109.1 |
| C5—C4—C10 | 118.4 (3) | C10i—C9—H9B | 109.1 |
| C3—C4—C10 | 123.0 (3) | H9A—C9—H9B | 107.8 |
| C6—C5—C4 | 121.1 (3) | C4—C10—C9i | 113.1 (3) |
| C6—C5—H5 | 119.5 | C4—C10—H10A | 109.0 |
| C4—C5—H5 | 119.5 | C9i—C10—H10A | 109.0 |
| C5—C6—C7 | 120.7 (3) | C4—C10—H10B | 109.0 |
| C5—C6—H6 | 119.6 | C9i—C10—H10B | 109.0 |
| C7—C6—H6 | 119.6 | H10A—C10—H10B | 107.8 |
| Symmetry codes: (i) −x+2, −y+1, −z+1. |
We are grateful to the French Ministère de la Recherche et Technologie for a PhD grant for SC. The CNRS is acknowledged for financial support. CS thanks the DFG for financial support. CD thanks the Studienstiftung des deutschen Volkes for a doctoral scholarship.
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In the context of our research in developing novel π-conjugated functionalized [2.2]paracyclophanes and ferrocenes (Clément et al., 2007a) for potential applications in coordination chemistry, we have recently reported an alternative to the classical Sonogashira synthesis (Morisaki et al., 2003) for the synthesis of ethynyl functionalized [2.2]paracyclophanes (Scheme 2). Our route involves a Corey-Fuchs reaction (Clément et al., 2007b) and subsequent dehydobromation induced by a strong base. In the first step, an ylide species, formed in situ by the interaction of zinc dust, CBr4 and PPh3, reacts with the formyl derivative 1a or 1b leading to the dibromoolefin derivatives 2a or 2b. The molecular structure of the vinylic intermediate 2b was elucidated by an single-crystal X-ray diffraction study (Figure 1).
2 b possesses a crystallographic center of inversion in the middle of the cyclophane framework. Bond lengths and angles may be considered as normal. Distortions typical of [2.2]paracyclophane systems, e.g. lengthened C—C bonds and widened angles in the bridges, narrowed ring bond angles at the bridgehead atoms, and boat-like distortion of the rings (the bridgehead atoms lie significantly out of the plane of the other four ring atoms) are observed. As previously noticed for the monodibromoolefin compound 2a, the alkenyl unit of 2b is strongly tilted. The two best planes of the arene (C3, C4, C5, C6, C7, C8; plane 1) and the vinyl-group (Br1, Br2, C1, C2; plane 2) possess a cutting angle of the normals of 49.4 (5)°
Contrary to a recently published, related system, no significant intermolecular interactions are observed for 2b due to inproper orientation of the molecules relative to each other (Hopf et al., 2007).
In the light of our recent work on the reactivity of (2,2-dibromovinyl)ferrocene towards thiolates (Clément et al., 2007b), the vinylic intermediates 2a and 2b should be promising starting materials for building new ligand systems. Synthesis, reactivity and photochemical properties of these new compounds will be reported in due course.