organic compounds
2,3,5,6-Tetrafluoro-1,4-bis(trimethylsilyl)benzene
aInstitut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany, bInstitut für Anorganische Chemie und Strukturchemie, Lehrstuhl II: Material- und Strukturforschung, Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1, D-40225 Düsseldorf, Germany, and cInstitut für Anorganische Chemie, Universität Duisburg-Essen, Lotharstrasse 1, D-47048 Duisburg, Germany
*Correspondence e-mail: maik.finze@uni-wuerzburg.de
The 12H18F4Si2, contains two independent molecules, both lying on inversion centers. The Carene—Si distances are significantly longer than in the analogous non-fluorinated compound. The packing of the molecules results in a herringbone motif in the ac plane.
of the title compound, CRelated literature
For the synthesis and chemistry of 1,4-(Me3Si)2—C6F4, see: Fearon & Gilman (1967); Tamborski & Soloski (1969); Fields et al. (1970); Sartori & Frohn (1974); Bardin et al. (1991); Frohn et al. (1998); Kashiwabara & Tanaka (2006). For related structures see: Rehm et al. (1999); Sekiguchi et al. (2000); Haberecht et al. (2002, 2004); Krumm et al. (2005); Hanamoto et al. (2006).
Experimental
Crystal data
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Data collection
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Refinement
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Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).
Supporting information
10.1107/S1600536812010677/mw2055sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536812010677/mw2055Isup2.hkl
Supporting information file. DOI: 10.1107/S1600536812010677/mw2055Isup3.cml
The starting material poly(cadmium-2,3,5,6-tetrafluorobenzene), [1,4-Cd—C6F4]n, was synthesized by thermolysis of Cd(1,4-O2C—C6F4) at 270 °C under vacuum according to a literature procedure (Sartori & Frohn, 1974).
7.1 g (27.3 mmol) poly(cadmium-2,3,5,6-tetrafluorobenzene), [1,4-Cd—C6F4]n, was charged into a Duran-glass Carius tube inside a
6.55 g (60.3 mmol) freshly distilled (CH3)3SiCl was added under protection of dry nitrogen. The tube was sealed and shaken and heated inside an oven. The temperature was increased stepwise over 30 h to 222°C without visual change of the reaction components. Further heating from 230 to 250°C over 26 h was accompanied by a reduction of the liquid phase and a change of the color to light grey. The Carius tube was cooled stepwise to -78°C before opening under nitrogen protection. CAUTION: Handling of the sealed Carius tube should proceed behind a large protection screen with long-sleeve leather gloves. At 0°C 3.4 g (31.3 mmol) of (CH3)3SiCl were recovered by condensation under high-vacuum. The dark grey solid residue, which contained the co-product CdCl2, was extracted with boiling petrol ether (60–70°C fraction). After removing the solvent from the extract a slightly brownish oil remained which was sublimed under high vacuum. The colorless crystals were collected on a water cooled finger. Yield ca 80%; mp 46°C [31–32°C isomeric mixture (Fields et al., 1970)]; NMR (20% CCl4 solution): 1H -0.39 p.p.m., 19F -124.2 p.p.m.; MS (EI, 73 eV) M+. 294, the fragment ions 81 (CH3SiF2), 77 ((CH3)2SiF), and 73 ((CH3)3Si) possessed higher intensities than the IR (neat): 2946 (m), 2889 (m), 1575 (w), 1487 (w), 1400 (st, b), 1343 (w), 1334 (w), 1286 (w), 1240 (st), 1214 (st), 1183 (m), 1035 (w), 921 (st), 830 (st, b), 748 (st), 684 (m), 613 (m), 566 (w), 432 (w).Methyl H atoms were identified in a difference map, idealized and refined using rigid groups allowed to rotate about the Si—C bond (AFIX 137 option of the SHELXL97 program). All Uiso(H) values were refined unrestrictedly.
The first synthesis of the title compound 1,4-bis(trimethylsilyl)tetrafluorobenzene, 1,4-(Me3Si)2—C6F4, was reported in 1967 starting from 1,2,4,5-tetrafluorobenzene, n-butyl lithium, and trimethylsilyl chloride (Fearon & Gilman 1967). Later, the compound was observed as a by-product in related reactions, improved methods for its selective synthesis were published and some reactions of 1,4-(Me3Si)2—C6F4 were described (Tamborski & Soloski, 1969; Fields et al. 1970; Sartori & Frohn, 1974; Bardin et al. 1991; Frohn et al. 1998; Kashiwabara & Tanaka, 2006). The 1,4-(Me3Si)2—C6F4 employed in the present study was prepared by a different route using poly(cadmium-2,3,5,6-tetrafluorobenzene), [1,4-Cd—C6F4]n, and trimethylsilyl chloride as starting materials.
The title compound 1,4-bis(trimethylsilyl)tetrafluorobenzene (Figure 1) crystallizes in the monoclinic
P21/c with two independent molecules each of which is located on a center of symmetry. Both crystallographically independent molecules display very similar geometric parameters. The C–C, Cmethyl–Si and C–F bond lengths are in the expected range. Both Carene–Si distances are slightly longer than those found for the non-fluorinated analogue 1,4-(Me3Si)2—C6H4 [d(Carene–Si) = 1.8817 (12) Å] (Haberecht et al. 2004) and other non-fluorinated Me3Si–Carene compounds (Haberecht et al. 2004; Rehm et al. 1999). In contrast, for related 1-trimethylsilyl-2,3,5,6-tetrafluoro benzene fragments similar values were reported (Sekiguchi et al. 2000, Krumm et al. 2005). In the closely related compound 1,2,4-(iPr3Si)3—C6F3 (Hanamoto et al. 2006) the d(Carene–Si) of the iPr3Si groups in ortho positions [d(C–Si) = 1.937 (2), 1.934 (2)] are significantly longer than those in the title compound whereas the third Carene–Si distance [d(C–Si) = 1.914 (2) Å], which corresponds to the iPr3Si group that has two F atoms in the ortho positions, is close to the values determined for 1,4-(Me3Si)2—C6F4.The 1,4-bis(trimethylsilyl)tetrafluorobenzene molecules are arranged in the ac plane to form a herringbone structure (Figure 2). The trimethylsilyl groups are interlinked by van der Waals interactions with methyl groups of neighboring molecules.
For the synthesis and chemistry of 1,4-(Me3Si)2—C6F4, see: Fearon & Gilman (1967); Tamborski & Soloski (1969); Fields et al. (1970); Sartori & Frohn (1974); Bardin et al. (1991); Frohn et al. (1998); Kashiwabara & Tanaka (2006). For related structures see: Rehm et al. (1999); Sekiguchi et al. (2000); Haberecht et al. (2002, 2004); Krumm et al. (2005); Hanamoto et al. (2006).
Data collection: CrysAlis PRO (Oxford Diffraction, 2009); cell
CrysAlis PRO (Oxford Diffraction, 2009); data reduction: CrysAlis PRO (Oxford Diffraction, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).C12H18F4Si2 | F(000) = 616 |
Mr = 294.44 | Dx = 1.314 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2ybc | Cell parameters from 8162 reflections |
a = 19.8389 (4) Å | θ = 3.1–28.3° |
b = 6.35013 (10) Å | µ = 0.26 mm−1 |
c = 12.3827 (2) Å | T = 199 K |
β = 107.407 (2)° | Block, colourless |
V = 1488.53 (5) Å3 | 0.25 × 0.22 × 0.20 mm |
Z = 4 |
Oxford Xcalibur Eos diffractometer | 2496 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.015 |
Equatorial mounted graphite monochromator | θmax = 25.0°, θmin = 3.2° |
Detector resolution: 16.2711 pixels mm-1 | h = −22→23 |
ω–scan | k = −7→7 |
8888 measured reflections | l = −14→12 |
2626 independent reflections |
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)] = 0.027 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.068 | H-atom parameters constrained |
S = 1.09 | w = 1/[σ2(Fo2) + (0.0284P)2 + 1.0425P] where P = (Fo2 + 2Fc2)/3 |
2626 reflections | (Δ/σ)max < 0.001 |
187 parameters | Δρmax = 0.39 e Å−3 |
0 restraints | Δρmin = −0.22 e Å−3 |
C12H18F4Si2 | V = 1488.53 (5) Å3 |
Mr = 294.44 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 19.8389 (4) Å | µ = 0.26 mm−1 |
b = 6.35013 (10) Å | T = 199 K |
c = 12.3827 (2) Å | 0.25 × 0.22 × 0.20 mm |
β = 107.407 (2)° |
Oxford Xcalibur Eos diffractometer | 2496 reflections with I > 2σ(I) |
8888 measured reflections | Rint = 0.015 |
2626 independent reflections |
R[F2 > 2σ(F2)] = 0.027 | 0 restraints |
wR(F2) = 0.068 | H-atom parameters constrained |
S = 1.09 | Δρmax = 0.39 e Å−3 |
2626 reflections | Δρmin = −0.22 e Å−3 |
187 parameters |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 | ||
Si1 | 0.12486 (2) | 0.23395 (7) | 0.19607 (3) | 0.01427 (11) | |
C1 | −0.01679 (8) | 0.3116 (2) | 0.03692 (12) | 0.0145 (3) | |
F1 | −0.03838 (4) | 0.12566 (13) | 0.06873 (7) | 0.0203 (2) | |
C2 | 0.05291 (8) | 0.3765 (2) | 0.08187 (12) | 0.0139 (3) | |
C3 | 0.06680 (7) | 0.5691 (2) | 0.04012 (12) | 0.0141 (3) | |
F3 | 0.13382 (4) | 0.64624 (14) | 0.07568 (7) | 0.0199 (2) | |
C4 | 0.08544 (8) | 0.0143 (3) | 0.25580 (13) | 0.0224 (3) | |
H4A | 0.0484 | 0.0679 | 0.2834 | 0.034 (5)* | |
H4B | 0.1212 | −0.0499 | 0.3170 | 0.037 (5)* | |
H4C | 0.0663 | −0.0886 | 0.1979 | 0.037 (5)* | |
C5 | 0.19335 (8) | 0.1412 (3) | 0.13233 (13) | 0.0190 (3) | |
H5A | 0.2119 | 0.2592 | 0.1019 | 0.033 (5)* | |
H5B | 0.1727 | 0.0427 | 0.0728 | 0.030 (5)* | |
H5C | 0.2309 | 0.0738 | 0.1894 | 0.037 (5)* | |
C6 | 0.16406 (9) | 0.4291 (3) | 0.30949 (13) | 0.0241 (4) | |
H6A | 0.1858 | 0.5406 | 0.2794 | 0.044 (6)* | |
H6B | 0.1990 | 0.3611 | 0.3703 | 0.045 (6)* | |
H6C | 0.1276 | 0.4864 | 0.3373 | 0.042 (6)* | |
Si2 | 0.35988 (2) | 0.79571 (7) | 0.56124 (3) | 0.01519 (11) | |
C7 | 0.50606 (8) | 0.8812 (2) | 0.59251 (12) | 0.0156 (3) | |
F7 | 0.51552 (5) | 0.76178 (15) | 0.68697 (7) | 0.0227 (2) | |
C8 | 0.43772 (8) | 0.9180 (2) | 0.52347 (12) | 0.0147 (3) | |
C9 | 0.43451 (7) | 1.0409 (2) | 0.42942 (12) | 0.0152 (3) | |
F9 | 0.37103 (4) | 1.08933 (14) | 0.35422 (7) | 0.0203 (2) | |
C10 | 0.36292 (9) | 0.8818 (3) | 0.70638 (13) | 0.0235 (4) | |
H10A | 0.3604 | 1.0326 | 0.7086 | 0.038 (6)* | |
H10B | 0.4063 | 0.8348 | 0.7594 | 0.032 (5)* | |
H10C | 0.3237 | 0.8222 | 0.7259 | 0.039 (6)* | |
C11 | 0.27524 (8) | 0.8855 (3) | 0.46024 (13) | 0.0214 (3) | |
H11A | 0.2727 | 0.8394 | 0.3853 | 0.031 (5)* | |
H11B | 0.2729 | 1.0364 | 0.4617 | 0.030 (5)* | |
H11C | 0.2365 | 0.8269 | 0.4816 | 0.034 (5)* | |
C12 | 0.36891 (9) | 0.5045 (3) | 0.55206 (14) | 0.0235 (4) | |
H12A | 0.3661 | 0.4662 | 0.4758 | 0.042 (6)* | |
H12B | 0.3316 | 0.4365 | 0.5734 | 0.049 (6)* | |
H12C | 0.4137 | 0.4610 | 0.6022 | 0.036 (5)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Si1 | 0.0148 (2) | 0.0168 (2) | 0.0121 (2) | 0.00203 (16) | 0.00533 (16) | 0.00124 (16) |
C1 | 0.0186 (7) | 0.0128 (7) | 0.0152 (7) | −0.0018 (6) | 0.0099 (6) | 0.0001 (6) |
F1 | 0.0192 (5) | 0.0163 (5) | 0.0258 (5) | −0.0034 (4) | 0.0073 (4) | 0.0062 (4) |
C2 | 0.0158 (7) | 0.0160 (7) | 0.0121 (7) | 0.0017 (6) | 0.0074 (6) | −0.0015 (6) |
C3 | 0.0114 (7) | 0.0177 (7) | 0.0144 (7) | −0.0023 (6) | 0.0057 (6) | −0.0030 (6) |
F3 | 0.0124 (4) | 0.0215 (5) | 0.0247 (5) | −0.0043 (4) | 0.0041 (4) | 0.0018 (4) |
C4 | 0.0210 (8) | 0.0264 (9) | 0.0213 (8) | 0.0043 (7) | 0.0089 (6) | 0.0093 (7) |
C5 | 0.0189 (8) | 0.0216 (8) | 0.0186 (7) | 0.0019 (6) | 0.0085 (6) | 0.0008 (6) |
C6 | 0.0262 (9) | 0.0271 (9) | 0.0162 (8) | 0.0050 (7) | 0.0019 (7) | −0.0033 (7) |
Si2 | 0.0138 (2) | 0.0159 (2) | 0.0169 (2) | −0.00165 (16) | 0.00616 (16) | −0.00042 (16) |
C7 | 0.0187 (8) | 0.0144 (7) | 0.0135 (7) | 0.0006 (6) | 0.0045 (6) | 0.0025 (6) |
F7 | 0.0190 (5) | 0.0288 (5) | 0.0191 (5) | −0.0001 (4) | 0.0039 (4) | 0.0117 (4) |
C8 | 0.0156 (7) | 0.0134 (7) | 0.0156 (7) | −0.0005 (6) | 0.0055 (6) | −0.0020 (6) |
C9 | 0.0122 (7) | 0.0159 (7) | 0.0153 (7) | 0.0020 (6) | 0.0006 (6) | −0.0009 (6) |
F9 | 0.0124 (4) | 0.0260 (5) | 0.0192 (4) | 0.0008 (4) | 0.0000 (3) | 0.0064 (4) |
C10 | 0.0260 (9) | 0.0264 (9) | 0.0209 (8) | −0.0044 (7) | 0.0116 (7) | −0.0012 (7) |
C11 | 0.0157 (8) | 0.0254 (9) | 0.0240 (8) | −0.0011 (6) | 0.0075 (6) | −0.0006 (7) |
C12 | 0.0237 (8) | 0.0185 (8) | 0.0299 (9) | −0.0019 (7) | 0.0105 (7) | 0.0003 (7) |
Si1—C4 | 1.8574 (16) | Si2—C11 | 1.8579 (16) |
Si1—C5 | 1.8595 (15) | Si2—C10 | 1.8620 (16) |
Si1—C6 | 1.8602 (16) | Si2—C12 | 1.8644 (17) |
Si1—C2 | 1.9101 (15) | Si2—C8 | 1.9077 (15) |
C1—F1 | 1.3539 (17) | C7—F7 | 1.3591 (17) |
C1—C3i | 1.379 (2) | C7—C9ii | 1.378 (2) |
C1—C2 | 1.390 (2) | C7—C8 | 1.389 (2) |
C2—C3 | 1.387 (2) | C8—C9 | 1.387 (2) |
C3—F3 | 1.3605 (16) | C9—F9 | 1.3587 (16) |
C3—C1i | 1.379 (2) | C9—C7ii | 1.378 (2) |
C4—H4A | 0.9600 | C10—H10A | 0.9600 |
C4—H4B | 0.9600 | C10—H10B | 0.9600 |
C4—H4C | 0.9600 | C10—H10C | 0.9600 |
C5—H5A | 0.9600 | C11—H11A | 0.9600 |
C5—H5B | 0.9600 | C11—H11B | 0.9600 |
C5—H5C | 0.9600 | C11—H11C | 0.9600 |
C6—H6A | 0.9600 | C12—H12A | 0.9600 |
C6—H6B | 0.9600 | C12—H12B | 0.9600 |
C6—H6C | 0.9600 | C12—H12C | 0.9600 |
C4—Si1—C5 | 112.29 (7) | C11—Si2—C10 | 108.76 (7) |
C4—Si1—C6 | 109.29 (8) | C11—Si2—C12 | 110.31 (8) |
C5—Si1—C6 | 109.76 (7) | C10—Si2—C12 | 111.96 (8) |
C4—Si1—C2 | 109.89 (7) | C11—Si2—C8 | 110.18 (7) |
C5—Si1—C2 | 108.36 (7) | C10—Si2—C8 | 108.80 (7) |
C6—Si1—C2 | 107.11 (7) | C12—Si2—C8 | 106.81 (7) |
F1—C1—C3i | 117.10 (13) | F7—C7—C9ii | 117.62 (13) |
F1—C1—C2 | 120.37 (13) | F7—C7—C8 | 118.79 (13) |
C3i—C1—C2 | 122.53 (14) | C9ii—C7—C8 | 123.58 (14) |
C3—C2—C1 | 113.39 (13) | C9—C8—C7 | 113.74 (13) |
C3—C2—Si1 | 120.39 (11) | C9—C8—Si2 | 126.70 (11) |
C1—C2—Si1 | 126.13 (11) | C7—C8—Si2 | 119.55 (11) |
F3—C3—C1i | 117.22 (13) | F9—C9—C7ii | 117.13 (13) |
F3—C3—C2 | 118.72 (13) | F9—C9—C8 | 120.19 (13) |
C1i—C3—C2 | 124.06 (13) | C7ii—C9—C8 | 122.68 (13) |
Si1—C4—H4A | 109.5 | Si2—C10—H10A | 109.5 |
Si1—C4—H4B | 109.5 | Si2—C10—H10B | 109.5 |
H4A—C4—H4B | 109.5 | H10A—C10—H10B | 109.5 |
Si1—C4—H4C | 109.5 | Si2—C10—H10C | 109.5 |
H4A—C4—H4C | 109.5 | H10A—C10—H10C | 109.5 |
H4B—C4—H4C | 109.5 | H10B—C10—H10C | 109.5 |
Si1—C5—H5A | 109.5 | Si2—C11—H11A | 109.5 |
Si1—C5—H5B | 109.5 | Si2—C11—H11B | 109.5 |
H5A—C5—H5B | 109.5 | H11A—C11—H11B | 109.5 |
Si1—C5—H5C | 109.5 | Si2—C11—H11C | 109.5 |
H5A—C5—H5C | 109.5 | H11A—C11—H11C | 109.5 |
H5B—C5—H5C | 109.5 | H11B—C11—H11C | 109.5 |
Si1—C6—H6A | 109.5 | Si2—C12—H12A | 109.5 |
Si1—C6—H6B | 109.5 | Si2—C12—H12B | 109.5 |
H6A—C6—H6B | 109.5 | H12A—C12—H12B | 109.5 |
Si1—C6—H6C | 109.5 | Si2—C12—H12C | 109.5 |
H6A—C6—H6C | 109.5 | H12A—C12—H12C | 109.5 |
H6B—C6—H6C | 109.5 | H12B—C12—H12C | 109.5 |
F1—C1—C2—C3 | 179.45 (12) | F7—C7—C8—C9 | −179.74 (13) |
C3i—C1—C2—C3 | −1.0 (2) | C9ii—C7—C8—C9 | 0.1 (2) |
F1—C1—C2—Si1 | −3.9 (2) | F7—C7—C8—Si2 | −1.36 (19) |
C3i—C1—C2—Si1 | 175.56 (11) | C9ii—C7—C8—Si2 | 178.52 (12) |
C4—Si1—C2—C3 | 167.71 (11) | C11—Si2—C8—C9 | −5.61 (16) |
C5—Si1—C2—C3 | −69.26 (13) | C10—Si2—C8—C9 | −124.75 (14) |
C6—Si1—C2—C3 | 49.09 (13) | C12—Si2—C8—C9 | 114.22 (14) |
C4—Si1—C2—C1 | −8.68 (15) | C11—Si2—C8—C7 | 176.25 (12) |
C5—Si1—C2—C1 | 114.36 (13) | C10—Si2—C8—C7 | 57.10 (14) |
C6—Si1—C2—C1 | −127.29 (13) | C12—Si2—C8—C7 | −63.93 (13) |
C1—C2—C3—F3 | −178.22 (12) | C7—C8—C9—F9 | 179.85 (13) |
Si1—C2—C3—F3 | 4.96 (18) | Si2—C8—C9—F9 | 1.6 (2) |
C1—C2—C3—C1i | 1.1 (2) | C7—C8—C9—C7ii | −0.1 (2) |
Si1—C2—C3—C1i | −175.76 (11) | Si2—C8—C9—C7ii | −178.38 (11) |
Symmetry codes: (i) −x, −y+1, −z; (ii) −x+1, −y+2, −z+1. |
Experimental details
Crystal data | |
Chemical formula | C12H18F4Si2 |
Mr | 294.44 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 199 |
a, b, c (Å) | 19.8389 (4), 6.35013 (10), 12.3827 (2) |
β (°) | 107.407 (2) |
V (Å3) | 1488.53 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.26 |
Crystal size (mm) | 0.25 × 0.22 × 0.20 |
Data collection | |
Diffractometer | Oxford Xcalibur Eos |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 8888, 2626, 2496 |
Rint | 0.015 |
(sin θ/λ)max (Å−1) | 0.595 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.027, 0.068, 1.09 |
No. of reflections | 2626 |
No. of parameters | 187 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.39, −0.22 |
Computer programs: CrysAlis PRO (Oxford Diffraction, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2011), publCIF (Westrip, 2010).
Si1—C2 | 1.9101 (15) | Si2—C8 | 1.9077 (15) |
C3—C2—Si1 | 120.39 (11) | C9—C8—Si2 | 126.70 (11) |
C1—C2—Si1 | 126.13 (11) | C7—C8—Si2 | 119.55 (11) |
Acknowledgements
This publication was funded by the German Research Foundation (DFG) and the University of Würzburg under the funding programme Open Access Publishing.
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The first synthesis of the title compound 1,4-bis(trimethylsilyl)tetrafluorobenzene, 1,4-(Me3Si)2—C6F4, was reported in 1967 starting from 1,2,4,5-tetrafluorobenzene, n-butyl lithium, and trimethylsilyl chloride (Fearon & Gilman 1967). Later, the compound was observed as a by-product in related reactions, improved methods for its selective synthesis were published and some reactions of 1,4-(Me3Si)2—C6F4 were described (Tamborski & Soloski, 1969; Fields et al. 1970; Sartori & Frohn, 1974; Bardin et al. 1991; Frohn et al. 1998; Kashiwabara & Tanaka, 2006). The 1,4-(Me3Si)2—C6F4 employed in the present study was prepared by a different route using poly(cadmium-2,3,5,6-tetrafluorobenzene), [1,4-Cd—C6F4]n, and trimethylsilyl chloride as starting materials.
The title compound 1,4-bis(trimethylsilyl)tetrafluorobenzene (Figure 1) crystallizes in the monoclinic space group P21/c with two independent molecules each of which is located on a center of symmetry. Both crystallographically independent molecules display very similar geometric parameters. The C–C, Cmethyl–Si and C–F bond lengths are in the expected range. Both Carene–Si distances are slightly longer than those found for the non-fluorinated analogue 1,4-(Me3Si)2—C6H4 [d(Carene–Si) = 1.8817 (12) Å] (Haberecht et al. 2004) and other non-fluorinated Me3Si–Carene compounds (Haberecht et al. 2004; Rehm et al. 1999). In contrast, for related 1-trimethylsilyl-2,3,5,6-tetrafluoro benzene fragments similar values were reported (Sekiguchi et al. 2000, Krumm et al. 2005). In the closely related compound 1,2,4-(iPr3Si)3—C6F3 (Hanamoto et al. 2006) the d(Carene–Si) of the iPr3Si groups in ortho positions [d(C–Si) = 1.937 (2), 1.934 (2)] are significantly longer than those in the title compound whereas the third Carene–Si distance [d(C–Si) = 1.914 (2) Å], which corresponds to the iPr3Si group that has two F atoms in the ortho positions, is close to the values determined for 1,4-(Me3Si)2—C6F4.
The 1,4-bis(trimethylsilyl)tetrafluorobenzene molecules are arranged in the ac plane to form a herringbone structure (Figure 2). The trimethylsilyl groups are interlinked by van der Waals interactions with methyl groups of neighboring molecules.