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The title compound, C16H30Si2, possesses crystallographic inversion symmetry. The allenic bond lengths are 1.309 (2) and 1.314 (2) Å.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536802022870/bt6216sup1.cif
Contains datablocks 2, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536802022870/bt62162sup2.hkl
Contains datablock 2

CCDC reference: 204674

Key indicators

  • Single-crystal X-ray study
  • T = 178 K
  • Mean [sigma](C-C) = 0.003 Å
  • R factor = 0.042
  • wR factor = 0.115
  • Data-to-parameter ratio = 24.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry








Comment top

As the cumulogues of conjugated dienes, conjugated bisallenes are of interest for preparative (e.g. as partners in cycloaddion reactions; Sankararaman et al., 2000) and structural reasons. The structure of the parent system 1,2,4,5-hexatetraene in solution and in the gas phase has been described (Christensen et al., 1973; cf. Traetteberg et al., 1973). Since structural data for this class of hydrocarbons are still scarce, we decided to prepare 2,7-dimethyl-4,5-bis(trimethylsilyl)-octa-2,3,5,6-tetraene, (2), a fully substituted bis-allene, and investigate it by X-ray structural analysis. As a precursor we used 2,7-dimethyl-octa-2,4,5,6-tetraene, (1), whose solid-state structure we have reported recently (Jones et al., 2002).

The structure of (2) is shown in Fig. 1. The molecule possesse a crystallographic inversion centre at the midpoint of the C4—C4i bond. Bond lengths and angles [e.g. the allenic bond lengths of 1.309 (2) and 1.314 (2) Å] may be considered normal [cf. 1.3067 (16) and 1.3126 (16) Å in (1); Jones et al., 2002]. The planes C1/2/3/5 and Si/C3/4/4i are mutually perpendicular [interplanar angle 88.49 (8)°].

The packing (Fig. 2) is unexceptional. The shortest H···H contacts are H6A···H8A(1 − x, 1 − y, −z) = 2.53 Å and H7B···H8C(1 + x, y, z) = 2.52 Å.

Experimental top

Compound (1) was metallated with n-butyllithium in THF in the presence of tetramethylethylenediamine and the resulting dianion was then quenched with trimethylsilylchloride (Stamm, 1992). Recrystallization of (2) from pentane afforded single crystals.

Refinement top

Methyl H atoms were identified in difference syntheses, idealized and then refined using rigid methyl groups (C—H = 0.98 Å and H—C—H = 109.5°) being allowed to rotate but not tip.

Computing details top

Data collection: P3 (Nicolet, 1987); cell refinement: P3; data reduction: XDISK (Nicolet, 1987); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1994); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The molecule of compound (2) in the crystal. Ellipsoids represent 50% probability levels. H-atom radii are arbitrary.
[Figure 2] Fig. 2. The packing of compound (2), projected parallel to the x axis. Radii are arbitrary.
2,7-Dimethyl-4,5-bis(trimethylsilyl)octa-2,3,5,6-tetraene top
Crystal data top
C16H30Si2Z = 1
Mr = 278.58F(000) = 154
Triclinic, P1Dx = 0.986 Mg m3
a = 6.363 (2) ÅMo Kα radiation, λ = 0.71073 Å
b = 8.963 (2) ÅCell parameters from 50 reflections
c = 9.157 (3) Åθ = 10–11.5°
α = 70.76 (2)°µ = 0.18 mm1
β = 72.13 (2)°T = 178 K
γ = 83.41 (2)°Prism, colourless
V = 469.2 (2) Å30.70 × 0.25 × 0.15 mm
Data collection top
Nicolet R3
diffractometer
Rint = 0.015
Radiation source: fine-focus sealed tubeθmax = 27.6°, θmin = 3.4°
Graphite monochromatorh = 08
ω scansk = 1111
2355 measured reflectionsl = 1111
2162 independent reflections3 standard reflections every 147 reflections
1613 reflections with I > 2σ(I) intensity decay: none
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.042Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.115H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.056P)2 + 0.1101P]
where P = (Fo2 + 2Fc2)/3
2162 reflections(Δ/σ)max < 0.001
87 parametersΔρmax = 0.29 e Å3
0 restraintsΔρmin = 0.21 e Å3
Crystal data top
C16H30Si2γ = 83.41 (2)°
Mr = 278.58V = 469.2 (2) Å3
Triclinic, P1Z = 1
a = 6.363 (2) ÅMo Kα radiation
b = 8.963 (2) ŵ = 0.18 mm1
c = 9.157 (3) ÅT = 178 K
α = 70.76 (2)°0.70 × 0.25 × 0.15 mm
β = 72.13 (2)°
Data collection top
Nicolet R3
diffractometer
Rint = 0.015
2355 measured reflections3 standard reflections every 147 reflections
2162 independent reflections intensity decay: none
1613 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0420 restraints
wR(F2) = 0.115H-atom parameters constrained
S = 1.02Δρmax = 0.29 e Å3
2162 reflectionsΔρmin = 0.21 e Å3
87 parameters
Special details top

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.

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

0.4358 (0.0072) x − 6.8427 (0.0071) y + 3.2746 (0.0099) z = 1.3751 (0.0083)

* −0.0006 (0.0005) C1 * 0.0018 (0.0016) C2 * −0.0007 (0.0006) C3 * −0.0006 (0.0005) C5

Rms deviation of fitted atoms = 0.0010

5.2707 (0.0040) x + 4.1904 (0.0062) y + 6.7925 (0.0053) z = 6.0327 (0.0022)

Angle to previous plane (with approximate e.s.d.) = 88.49 (0.08)

* 0.0009 (0.0005) Si * 0.0013 (0.0007) C3 * −0.0035 (0.0018) C4 * 0.0012 (0.0006) C4_1

Rms deviation of fitted atoms = 0.0020

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Si0.54749 (9)0.25475 (6)0.30629 (6)0.03061 (17)
C10.1248 (3)0.1335 (2)0.7153 (3)0.0415 (5)
H1A0.12670.08540.63390.050*
H1B0.19340.23900.69150.050*
H1C0.20720.06750.82240.050*
C20.1105 (3)0.1468 (2)0.7125 (2)0.0317 (4)
C30.2782 (3)0.1071 (2)0.6064 (2)0.0298 (4)
C40.4466 (3)0.08035 (19)0.4915 (2)0.0270 (4)
C50.1435 (4)0.2093 (3)0.8380 (2)0.0450 (5)
H5A0.30170.21110.82600.054*
H5B0.06880.14070.94610.054*
H5C0.08150.31670.82350.054*
C60.5172 (4)0.2187 (3)0.1249 (2)0.0434 (5)
H6A0.36000.21530.13440.052*
H6B0.58830.11760.11690.052*
H6C0.58730.30410.02800.052*
C70.8426 (3)0.2927 (2)0.2743 (3)0.0429 (5)
H7A0.92920.19480.27570.052*
H7B0.85490.33000.36060.052*
H7C0.89900.37340.16970.052*
C80.3795 (4)0.4324 (2)0.3365 (3)0.0426 (5)
H8A0.44280.52650.24760.051*
H8B0.37980.44430.43900.051*
H8C0.22750.41990.33860.051*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Si0.0334 (3)0.0273 (3)0.0284 (3)0.00164 (19)0.0086 (2)0.00493 (19)
C10.0378 (11)0.0394 (11)0.0430 (11)0.0052 (9)0.0068 (9)0.0138 (9)
C20.0382 (10)0.0243 (8)0.0285 (9)0.0026 (7)0.0054 (8)0.0079 (7)
C30.0355 (10)0.0240 (8)0.0288 (9)0.0001 (7)0.0102 (7)0.0060 (7)
C40.0313 (9)0.0246 (8)0.0252 (8)0.0006 (7)0.0085 (7)0.0075 (7)
C50.0558 (13)0.0409 (11)0.0388 (11)0.0024 (10)0.0058 (10)0.0198 (9)
C60.0505 (13)0.0463 (12)0.0303 (10)0.0032 (10)0.0115 (9)0.0073 (9)
C70.0396 (11)0.0379 (10)0.0463 (12)0.0063 (9)0.0108 (9)0.0062 (9)
C80.0483 (12)0.0286 (9)0.0467 (12)0.0010 (9)0.0151 (10)0.0056 (8)
Geometric parameters (Å, º) top
Si—C61.861 (2)C5—H5A0.9800
Si—C71.863 (2)C5—H5B0.9800
Si—C81.864 (2)C5—H5C0.9800
Si—C41.8834 (18)C6—H6A0.9800
C1—C21.507 (3)C6—H6B0.9800
C1—H1A0.9800C6—H6C0.9800
C1—H1B0.9800C7—H7A0.9800
C1—H1C0.9800C7—H7B0.9800
C2—C31.309 (2)C7—H7C0.9800
C2—C51.510 (3)C8—H8A0.9800
C3—C41.314 (2)C8—H8B0.9800
C4—C4i1.501 (3)C8—H8C0.9800
C6—Si—C7109.49 (10)C2—C5—H5C109.5
C6—Si—C8109.11 (10)H5A—C5—H5C109.5
C7—Si—C8108.70 (10)H5B—C5—H5C109.5
C6—Si—C4110.50 (9)Si—C6—H6A109.5
C7—Si—C4110.35 (9)Si—C6—H6B109.5
C8—Si—C4108.66 (9)H6A—C6—H6B109.5
C2—C1—H1A109.5Si—C6—H6C109.5
C2—C1—H1B109.5H6A—C6—H6C109.5
H1A—C1—H1B109.5H6B—C6—H6C109.5
C2—C1—H1C109.5Si—C7—H7A109.5
H1A—C1—H1C109.5Si—C7—H7B109.5
H1B—C1—H1C109.5H7A—C7—H7B109.5
C3—C2—C1121.97 (17)Si—C7—H7C109.5
C3—C2—C5121.48 (18)H7A—C7—H7C109.5
C1—C2—C5116.55 (16)H7B—C7—H7C109.5
C2—C3—C4174.86 (18)Si—C8—H8A109.5
C3—C4—C4i121.56 (19)Si—C8—H8B109.5
C3—C4—Si116.38 (13)H8A—C8—H8B109.5
C4i—C4—Si122.06 (16)Si—C8—H8C109.5
C2—C5—H5A109.5H8A—C8—H8C109.5
C2—C5—H5B109.5H8B—C8—H8C109.5
H5A—C5—H5B109.5
C6—Si—C4—C3117.95 (15)C6—Si—C4—C4i62.6 (2)
C7—Si—C4—C3120.81 (16)C7—Si—C4—C4i58.6 (2)
C8—Si—C4—C31.73 (18)C8—Si—C4—C4i177.68 (18)
Symmetry code: (i) x+1, y, z+1.

Experimental details

Crystal data
Chemical formulaC16H30Si2
Mr278.58
Crystal system, space groupTriclinic, P1
Temperature (K)178
a, b, c (Å)6.363 (2), 8.963 (2), 9.157 (3)
α, β, γ (°)70.76 (2), 72.13 (2), 83.41 (2)
V3)469.2 (2)
Z1
Radiation typeMo Kα
µ (mm1)0.18
Crystal size (mm)0.70 × 0.25 × 0.15
Data collection
DiffractometerNicolet R3
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
2355, 2162, 1613
Rint0.015
(sin θ/λ)max1)0.651
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.042, 0.115, 1.02
No. of reflections2162
No. of parameters87
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.29, 0.21

Computer programs: P3 (Nicolet, 1987), P3, XDISK (Nicolet, 1987), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), XP (Siemens, 1994), SHELXL97.

Selected geometric parameters (Å, º) top
C2—C31.309 (2)C4—C4i1.501 (3)
C3—C41.314 (2)
C2—C3—C4174.86 (18)C3—C4—Si116.38 (13)
C3—C4—C4i121.56 (19)C4i—C4—Si122.06 (16)
Symmetry code: (i) x+1, y, z+1.
 

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